| 安達 千波矢（あだち ちはや） | データ更新日：2024.04.16 |
教授 ／
工学研究院
応用化学部門
| 1. | Takahiko Yamanaka, Hajime Nakanotani, Chihaya Adachi, The role of spontaneous orientation polarization on charge storage behavior at an interface between organic semiconductor layers, Journal of Materials Chemistry C, 10.1039/d3tc03979j, 12, 3, 1055-1060, 2023.12, Optically generated carriers are pinned at the organic/organic interface if the two organic layers have a large polarization difference, underlining that the combination of polar molecules is crucial to extend the carrier lifetime.. |
| 2. | Bhagya Madushani, Masashi Mamada, Kenichi Goushi, Thanh Ba Nguyen, Hajime Nakanotani, Hironori Kaji, Chihaya Adachi, Multiple donor–acceptor design for highly luminescent and stable thermally activated delayed fluorescence emitters, Scientific Reports, 10.1038/s41598-023-34623-9, 13, 1, 2023.05, Abstract A considerable variety of donor–acceptor (D–A) combinations offers the potential for realizing highly efficient thermally activated delayed fluorescence (TADF) materials. Multiple D–A type compounds are one of the promising families of TADF materials in terms of stability as well as efficiencies. However, those emitters are always composed of carbazole-based donors despite a wide choice of moieties used in linearly linked single D–A molecules. Herein, we developed a multiple D–A type TADF compound with two distinct donor units of 9,10-dihydro-9,9-dimethylacridine (DMAC) and carbazole as the hetero-donor design. The new emitter exhibits high photoluminescence quantum yield (PLQY) in various conditions including polar media blend and high concentrations. Organic light-emitting diodes (OLEDs) showed a reasonably high external quantum efficiency (EQE). In addition, we revealed that the multiple-D–A type molecules showed better photostability than the single D–A type molecules, while the operational stability in OLEDs involves dominant other factors.. |
| 3. | Youichi Tsuchiya, Keito Mizukoshi, Masaki Saigo, Tomohiro Ryu, Kiyoshi Miyata, Ken Onda, Chihaya Adachi, Luminescence mechanism analysis of a TADF molecule showing peculiar thermal behavior, Faraday Discussions, 10.1039/d3fd00151b, 250, 233-250, 2023.11, 9-[1,4]Benzoxaborino[2,3,4-kl]phenoxaborine-7-yl-1,3,6,8-tetramethyl-9H-carbazole, a donor–acceptor linked TADF molecule with a very short delay lifetime of 750 ns, exhibits a peculiar thermal behavior similar to that of negative gap materials.. |
| 4. | Ilene Allison, Mashashi Mamada, Atul Shukla, Sarah K. M. McGregor, Ras Baizureen Roseli, Innes Gale, Vijay P. Rahane, Evan G. Moore, Elizabeth H. Krenske, Nidhi Jain, Chihaya Adachi, Ebinazar B. Namdas, Shih-Chun Lo, Light blue rigid excited-state intramolecular proton transfer organic semiconductor laser chromophores, Journal of Materials Chemistry C, 10.1039/d3tc02707d, 11, 45, 15861-15872, 2023.11, The effect of excited-state intramolecular proton-transfer (ESIPT) laser material rigidity on photophysical properties and amplified spontaneous emission (ASE) thresholds (EASEth) is studied.. |
| 5. | Long Chen, Xun Tang, Ruihong Liu, Qi Zheng, Youjun Yu, Dongying Zhou, Shengyi Yang, Chihaya Adachi, Liangsheng Liao, Zuoquan Jiang, Double-locked narrowband hybrid locally-excited and charge-transfer emitter exhibiting amplified spontaneous emission, The Innovation Materials, 10.59717/j.xinn-mater.2023.100026, 1, 2, 100026-100026, 2023.09, <p>Hybrid Locally-excited and Charge-Transfer (HLCT) materials have garnered significant attention for their high exciton utilization efficiency in organic light-emitting diodes (OLEDs). However, conventional HLCT materials suffer from broad emission, which limits their applications. In this study, we report a narrowband HLCT emitter, namely 10-(dimesitylboranyl)-8,8,12,12-tetraphenyl-8,12-dihydrobenzo[9,1]quinolizino[3,4,5,6,7-<i>klmn</i>]phenoxazine (PXZ-DL), incorporated by double-locked intramolecular connection. PXZ-DL exhibits a narrow emission spectrum with a small full width at half-maximum (FWHM) of 35 nm and 47 nm in solution and as an OLED emitter, respectively. Moreover, PXZ-DL demonstrates a high photoluminescence quantum yield of 100% and an external quantum efficiency of 8.0%. Additionally, PXZ-DL demonstrates excellent performance in amplified spontaneous emission with a low threshold of 5.7 ��J cm<sup>-2</sup> and a narrow FWHM of 11 nm. The intramolecular lock strategy offers a promising approach for the development of HLCT materials with high color purity.</p> . |
| 6. | John Marques dos Santos, Chin-Yiu Chan, Shi Tang, David Hall, Tomas Matulaitis, David B. Cordes, Alexandra M. Z. Slawin, Youichi Tsuchiya, Ludvig Edman, Chihaya Adachi, Yoann Olivier, Eli Zysman-Colman, Color tuning of multi-resonant thermally activated delayed fluorescence emitters based on fully fused polycyclic amine/carbonyl frameworks, Journal of Materials Chemistry C, 10.1039/d3tc00641g, 11, 24, 8263-8273, 2023.05, Two newly developed carboynyl-based multi-resonant TADF show bright green-yellow emission. These were used as emitters in both OLEDs, and LECs.. |
| 7. | Masayuki Shiochi, Hiroshi Fujimoto, Hin Wai Mo, Keiko Inoue, Yusaku Tanahashi, Hiroyuki Hosomi, Takashi Miyamoto, Hiroshi Miyazaki, Chihaya Adachi, Permeation of oxygen and water into a plasma-enhanced chemical vapor deposited silicon nitride film as function of deposition pressure, Journal of Vacuum Science & Technology B, 10.1116/6.0003050, 41, 6, 2023.10, In this work, we demonstrate that the permeability of a SiNx thin film (prepared by plasma-enhanced chemical vapor deposition) to water and oxygen is closely related to the deposition pressure. By dynamic secondary ion mass spectrometry, we confirmed that water penetration occurs into the SiNx film only in the oxidized layer. Furthermore, positron annihilation lifetime spectroscopy indicated that a SiNx film with a lower deposition pressure provides a smaller pore (free volume hole) radius, which is more effective in terms of blocking ambient molecular diffusion or penetration. The SiNx films were also applied as an encapsulation layer for organic light-emitting diodes; SiNx films with a lower deposition pressure exhibited higher encapsulation properties.. |
| 8. | Badamgarav Purev-Ochir, Xuelong Liu, Yuki Fujita, Dai Semba, Telugu Bhim Raju, Ganbaatar Tumen-Ulzii, Atsushi Wachi, Hiroshi Sato, Toshinori Matsushima, Chihaya Adachi, Oxygen‐Induced Reversible Degradation of Perovskite Solar Cells, Solar RRL, 10.1002/solr.202300127, 7, 14, 2023.06, After remarkable progress over the past decades, perovskite solar cells (PSCs) currently exhibit efficient solar power conversion efficiency. However, the environmental instability of perovskite materials and devices is still a serious issue, impeding the future commercialization of this technology. Herein, why PSCs degrade in air is investigated and it is found that one of the critical reasons for the air‐induced PSC degradation is the doping of the 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobi‐fluorene (spiro‐OMeTAD) hole‐transport layer with oxygen. Photoelectron yield spectroscopy reveals that the hole‐transport level of the spiro‐OMeTAD layer becomes deeper by oxygen doping, increasing an energy barrier for hole extraction. In other words, decreased hole extraction at the perovskite/spiro‐OMeTAD interface induces the degradation of PSCs in air. However, this oxygen‐induced degradation of PSCs is reversible to some extent by storing PSCs in a vacuum to remove oxygen. In contrast, no detectable degradation of the perovskite light absorber is observed after ≈600 h of air exposure from the results of morphological and structural characterizations. These aspects provide a deeper understanding of PSCs degradation, giving insight into improving long‐term durability in air in the future.. |
| 9. | Xuelong Liu, Narayanaswamy Kamatham, Zhangsheng Shi, Shidong Yu, Qing Ren, Kentaro Imaoka, Chin-Yiu Chan, Benoît Heinrich, Robin Troiville-Cazilhac, Lise-Marie Chamoreau, Lydia Sosa Vargas, David Kreher, Youichi Tsuchiya, Toshinori Matsushima, Xiankai Chen, Fabrice Mathevet, Chihaya Adachi, Investigation of Charge Transport Properties in a 2D Dion–Jacobson Halide Perovskite Based on Terphenyl Dications, ACS Materials Letters, 10.1021/acsmaterialslett.3c00509, 5, 8, 2148-2155, 2023.07. |
| 10. | Shoma Sasaki, Kenichi Goushi, Masashi Mamada, Shiori Miyazaki, Kiyoshi Miyata, Ken Onda, Chihaya Adachi, Indication of Intramolecular Triplet–Triplet Annihilation Upconversion in Organic Light‐Emitting Diodes, Advanced Optical Materials, 10.1002/adom.202301924, 12, 3, 2023.10, Abstract It is well known that triplet–triplet annihilation upconversion (TTU) can enhance electroluminescence (EL) efficiency by converting two low‐energy triplet excitons into one high‐energy singlet exciton. However, conventional intermolecular TTU requires high doping concentration to activate, limiting device architecture. Here, six dimer molecules comprised of two anthracene units connected by a spacer unit are investigated, which have a possibility of the intramolecular TTU process. As a result, two dimer molecules show high TTU efficiencies close to the theoretical maximum even in dispersed, diluted conditions. By comparing these molecular conformations, a correlation is found between the dimer structures of two anthracene units and the TTU activity in the diluted condition, i.e., the 3D molecular structure with the exciton utilizing efficiency.. |
| 11. | Shiori Miyazaki, Kenichi Goushi, Yuichi Kitagawa, Yasuchika Hasegawa, Chihaya Adachi, Kiyoshi Miyata, Ken Onda, Highly efficient light harvesting of a Eu(iii) complex in a host–guest film by triplet sensitization, Chemical Sciences, 10.1039/D3SC01817B, 2023.05. |
| 12. | Ryotaro Nasu, Xun Tang, Satoru Watanabe, Chathuranganie A. M. Senevirathne, Ganbaatar Tumen‐Ulzii, Toshinori Matsushima, Chihaya Adachi, Exciton Dynamics and Optically Pumped Lasing in 1‐Naphthylmethylamine‐Based Quasi‐2D Perovskite Films, Advanced Functional Materials, 10.1002/adfm.202301794, 33, 44, 2023.07, Abstract Films of the quasi‐2D perovskite based on 1‐naphthylmethylamine (NMA) are promising as the gain medium for optically pumped lasing and future electrically pumped lasing because of its low lasing threshold and small electroluminescence efficiency rolloff. However, reasons for the low threshold and small efficiency rolloff are still unclear. Therefore, exciton dynamics are investigated in NMA‐based quasi‐2D perovskite films. It is found that quenching of bright excitons by other excitons or charge carriers is unlikely in NMA‐based quasi‐2D perovskite films, which is one reason for the low lasing threshold and small efficiency rolloff. Moreover, thermally stimulated current measurements reveal that the defect levels inside the band gap of the NMA‐based quasi‐2D perovskite are shallow, with a depth of ≈0.3 eV, causing a decrease in nonradiative exciton recombination through the defects. Therefore, population inversion can be easily achieved, leading to the low lasing threshold as well. For fabrication of NMA‐based quasi‐2D perovskite laser devices with even lower lasing thresholds, a circular‐shaped optical resonator, and small‐molecule‐based defect passivation are used. Optically pumped lasing can be obtained from these devices, with a threshold of ≈1 µJ cm−2, which is one of the lowest values ever reported in any perovskite lasers.. |
| 13. | Thanh B. Nguyen, Hajime Nakanotani, Chin-Yiu Chan, Shunta Kakumachi, Chihaya Adachi, Enhancing Triplet–Triplet Upconversion Efficiency and Operational Lifetime in Blue Organic Light-Emitting Diodes by Utilizing Thermally Activated Delayed Fluorescence Materials, ACS Applied Materials & Interfaces, 10.1021/acsami.3c02855, 15, 19, 23557-23563, 2023.05. |
| 14. | Ganbaatar Tumen-Ulzii, Kotaro Takekuma, Yuki Fujita, Dai Senba, Chathuranganie A. M. Senevirathne, Yi-Ting Lee, Atsushi Wachi, Hiroshi Sato, Toshinori Matsushima, Chihaya Adachi, Development of a new hole transport material for perovskite solar cells, Applied Physics Letters, 10.1063/5.0150066, 122, 20, 2023.05, N,N-di(4-methoxyphenyl)amino-9,9′-spirobifluorene (spiro-OMeTAD) is a widely used hole transport layer (HTL) material for emerging lead halide hybrid perovskite solar cells (PSCs). Finding alternative HTL materials is required for the future development of more efficient and stable PSCs. Here, we developed a new HTL material of N2,N2,N,7N7-tetrakis(4-methoxyphenyl)benzo[b]benzo[4,5]thieno[2,3-d]thiophene-2,7-diamine (TBTD). Chemically doped TBTD provided better hole extraction in PSCs than chemically doped spiro-OMeTAD due to higher electrical conductivity and a more suitable hole transport energy level. Thus, PSCs with the TBTD HTL showed higher power conversion efficiency (∼21%) than spiro-OMeTAD HTL (∼19%). The operational stability of TBTD-based PSCs was similar to that of spiro-OMeTAD-based PSCs. The findings discussed in this study will aid in the future development of high-performance PSCs.. |
| 15. | Hyung Suk Kim, Sang Hoon Lee, Chihaya Adachi, Comparison of Exciton Annihilation Processes in Prototypical Charge-Transfer Molecules, The Journal of Physical Chemistry C, 10.1021/acs.jpcc.3c06465, 128, 3, 994-1002, 2023.11. |
| 16. | Shintaro Kohata, Hajime Nakanotani, Youhei Chitose, Takuma Yasuda, Youichi Tsuchiya, Chihaya Adachi, Anti‐Stokes Luminescence in Multi‐Resonance‐Type Thermally‐Activated Delayed Fluorescence Molecules, Angewandte Chemie International Edition, 10.1002/anie.202312326, 62, 44, 2023.09, Abstract Photon‐upconversion in organic molecular systems is one of the promising technologies for future energy harvesting systems because these systems can generate excitons that possess higher energy than excitation energy. The photon‐upconversion caused by absorbing ambient heat as additional energy is particularly interesting because it could ideally provide a light‐driving cooling system. However, only a few organic molecular systems have been reported. Here, we report the anti‐Stokes photoluminescence (ASPL) derived from hot‐band absorption in a series of multi‐resonance‐type thermally‐activated delayed fluorescence (MR‐TADF) molecules. The MR‐TADF molecules exhibited an anti‐Stokes shift of approximately 0.1 eV with a high PL quantum yield in the solution state. The anti‐Stokes shift corresponded well to the 1–0 vibration transition from the ground state to the excited singlet state, and we further evaluated a correlation between the activation energy for the ASPL intensity and the TADF process. Our demonstration underlines that MR‐TADF molecules have become a novel class of ASPL materials for various future applications, such as light‐driving cooling systems.. |
| 17. | Shunta Kakumachi, Thanh Ba Nguyen, Hajime Nakanotani, Chihaya Adachi, Abrupt exciton quenching in blue fluorescent organic light-emitting diodes around turn-on voltage region, Chemical Engineering Journal, 10.1016/j.cej.2023.144516, 471, 144516-144516, 2023.09. |
| 18. | Yuuhi Ueda, Masaki Tanaka, Hajime Nakanotani, Chihaya Adachi, A polar transition of spontaneous orientation polarization in organic amorphous thin films, Chemical Physics Letters, 10.1016/j.cplett.2023.140915, 833, 140915-140915, 2023.12. |
| 19. | Xun Tang, Mingchen Xie, Zesen Lin, Kirill Mitrofanov, Tuul Tsagaantsooj, Yi‐Ting Lee, Ryota Kabe, Atula S. D. Sandanayaka, Toshinori Matsushima, Takuji Hatakeyama, Chihaya Adachi, A Rigid Multiple Resonance Thermally Activated Delayed Fluorescence Core Toward Stable Electroluminescence and Lasing, Angewandte Chemie International Edition, 10.1002/anie.202315210, 63, 2, 2023.12, Abstract The investigation of organic light‐emitting diodes (OLEDs) and organic laser devices with thermally activated delayed fluorescence (TADF) molecules is emerging due to the potential of harnessing triplets. In this work, a boron/nitrogen multiple‐resonance TADF polycyclic framework fusing carbazole units (CzBNPh) was proposed. CzBNPh exhibited a narrowband emission (<30 nm), a unity photoluminescence quantum yield, and a fast radiative rate. Consequently, CzBNPh demonstrated a low distributed feedback (DFB) lasing threshold of 0.68 μJ cm−2. Furthermore, the stimulated emission zone of CzBNPh was effectively separated from its singlet and triplet absorption, thereby minimizing the singlet‐triplet annihilation under long‐pulsed excitation ranging from 20 μs to 2.5 ms. Significantly, the enhanced rigid molecular conformation, thermal stability, and photo‐stability resulted in improved lasing and electroluminescence stability compared to that of 5,9‐diphenyl‐5,9‐diaza‐13b‐boranaphtho[3,2,1‐de]anthracene (DABNA)‐core. These findings indicate the potential of CzBN‐core as a promising framework for achieving long‐pulsed wave and electrically‐pumped lasing in the future.. |
| 20. | Hyung Suk Kim, Sang Hoon Lee, Seunghyup Yoo, Chihaya Adachi, Understanding of complex spin up-conversion processes in charge-transfer-type organic molecules, Nature Communications, 10.1038/s41467-024-46406-5, 15, 1, 2024.03, Abstract Despite significant progress made over the past decade in thermally activated delayed fluorescence (TADF) molecules as a material paradigm for enhancing the performance of organic light-emitting diodes, the underlying spin-flip mechanism in these charge-transfer (CT)-type molecular systems remains an enigma, even since its initial report in 2012. While the initial and final electronic states involved in spin-flip between the lowest singlet and lowest triplet excited states are well understood, the exact dynamic processes and the role of intermediate high-lying triplet (T) states are still not fully comprehended. In this context, we propose a comprehensive model to describe the spin-flip processes applicable for a typical CT-type molecule, revealing the origin of the high-lying T state in a partial molecular framework in CT-type molecules. This work provides experimental and theoretical insights into the understanding of intersystem crossing for CT-type molecules, facilitating more precise control over spin-flip rates and thus advancing toward developing the next-generation platform for purely organic luminescent candidates.. |
| 21. | Nishiki Yamada, Hajime Nakanotani, Akitsuna Takagi, Masashi Mamada, Umamahesh Balijapalli, Tatsuya Ichikawa, Eiji Hirata, Shun Kaizu, Akira Tanaka, Kazuichiro Itonaga, Chihaya Adachi, Three-dimensional sensing of surfaces by projection of invisible electroluminescence from organic light-emitting diodes, Science Advances, 10.1126/sciadv.adj6583, 10, 1, 2024.01, Organic light-emitting diodes (OLEDs) that efficiently emit near-infrared (NIR) light and consume little power will create valuable applications for OLEDs beyond just displays. Here, we report such a NIR-OLED with high operational stability that can be used as a light source for three-dimensional sensing of object’s surfaces. Using a narrow-energy-gap material as a host for producing NIR hyperfluorescence system, we fabricated a NIR-OLED exhibiting intense emission at 930 nm with a high external electroluminescence quantum efficiency of more than 1% at a current density of 100 milliamperes per square meter without any degradation even after more than 300 hours of operation. The NIR-OLEDs were integrated with dense complementary metal-oxide semiconductor circuits to make a micro-NIR-OLED projector (0.21 inch, 230,400 pixels). By actively driving the projector on a pixel by pixel and projecting their emission onto objects, we successfully scanned and sensed the surfaces in three dimensions with invisible NIR.. |
| 22. | Yeonghoon Jin, Hyung Suk Kim, Donggyun Lee, Chihaya Adachi, Seunghyup Yoo, Kyoungsik Yu, Rigorous Determination of Dipole Orientation in Organic Thin Films Using Angle-Dependent Photoluminescence, The Journal of Physical Chemistry C, 10.1021/acs.jpcc.3c06330, 128, 4, 1755-1761, 2024.01. |
| 23. | Yanmei Hu, Alexander Civil, Yufang Li, Gerardus N. Iswara Lestanto, Youichi Tsuchiya, Chin‐Yiu Chan, Chihaya Adachi, Judicious Design of Pyridine‐Based Hosts for Stable, Efficient, and Low‐Driving Thermally Activated Delayed Fluorescence Organic Light‐Emitting Diodes, Advanced Optical Materials, 10.1002/adom.202302971, 2024.01, Abstract Although thermally activated delayed fluorescence (TADF) based organic light‐emitting diodes (OLEDs) continue to achieve high efficiencies, their device stability still does not necessarily meet industrial standards. To improve device stability, careful design of a stable host material is crucial. Herein, with reference to a common p‐type host material, 3,3′‐di(9H‐carbazol‐9‐yl)‐1,1′‐biphenyl (mCBP), three novel host materials based on a pyridine unit, mCBP‐1N, CzPyPhCz, and CzPyBF, are systematically designed to improve the stabilities efficiently. The green and blue TADF OLEDs are fabricated with these three new hosts. The maximum external quantum efficiencies (EQEmaxs) of green OLEDs are 20.3 % and 14.0% for CzPyBF and mCBP hosts, respectively. Further, high EQEs of 19.2% and 12.9% are maintained even at 1000 cd m−2. Most importantly, the device lifetime of the CzPyBF host can achieve LT95 of 62.7 h, which is 2.5 times longer than that of mCBP. Also, lower turn‐on voltages are achieved by using CzPyPhCz in blue and green devices. With host engineering, the TADF OLEDs are simultaneously improved with lower turn‐on voltages, higher EQEs, and longer device lifetimes.. |
| 24. | Ying-Chun Cheng, Xun Tang, Kai Wang, Xin Xiong, Xiao-Chun Fan, Shulin Luo, Rajat Walia, Yue Xie, Tao Zhang, Dandan Zhang, Jia Yu, Xian-Kai Chen, Chihaya Adachi, Xiao-Hong Zhang, Efficient, narrow-band, and stable electroluminescence from organoboron-nitrogen-carbonyl emitter, Nature Communications, 10.1038/s41467-024-44981-1, 15, 1, 2024.01, Abstract Organic light-emitting diodes (OLEDs) exploiting simple binary emissive layers (EMLs) blending only emitters and hosts have natural advantages in low-cost commercialization. However, previously reported OLEDs based on binary EMLs hardly simultaneously achieved desired comprehensive performances, e.g., high efficiency, low efficiency roll-off, narrow emission bands, and high operation stability. Here, we report a molecular-design strategy. Such a strategy leads to a fast reverse intersystem crossing rate in our designed emitter h-BNCO-1 of 1.79×105 s−1. An OLED exploiting a binary EML with h-BNCO-1 achieves ultrapure emission, a maximum external quantum efficiency of over 40% and a mild roll-off of 14% at 1000 cd·m−2. Moreover, h-BNCO-1 also exhibits promising operational stability in an alternative OLED exploiting a compact binary EML (the lifetime reaching 95% of the initial luminance at 1000 cd m−2 is ~ 137 h). Here, our work has thus provided a molecular-design strategy for OLEDs with promising comprehensive performance.. |
| 25. | Luxia Cui, Ami Horioka, Ryoichi Ishimatsu, Masashi Mamada, Chihaya Adachi, Keishiro Tahara, Yu Hoshino, Toshikazu Ono, Advanced Molecular Design for Efficient Multicolor Electrochemiluminescence and Amplified Spontaneous Emission based on Tetra-BF2 Complexes, Advanced Optical Materials, 10.1002/adom.202302803, 2024.01, Abstract Advanced organoboron dyes, incorporating tetra‐boron difluoride (tetra‐BF2) moieties, are developed, demonstrating efficient electrochemiluminescence (ECL) emissions in the green to orange regions through direct ion annihilation. By introducing diverse alkyl modifications in the molecules, luminescence color tuning is achieved via alterations in conjugation and bending angle. A photoluminescence quantum yield of 100% in dilute solutions is successfully achieved. Notably, the introduction of alkyl groups to the methine side stabilizes the radical ionic state, resulting in a high ECL efficiency of 74% through an efficient radical‐ion annihilation pathway. The key factor is that the energy of the annihilation reaction exceeds the S1 energy required for luminescence. Spin density calculations further elucidate the substituent effects on the radical ions of complexes. Moreover, the lasing properties of these materials in the solution‐processed blend films are investigated, revealing a low amplified spontaneous emission (ASE) threshold (Eth) of 6.40 ± 0.24 µJ cm−2, which is notably lower among organic laser materials. This is attributed to their large Stokes shifts and high quantum yield. The excellent ECL and ASE performances establish these materials as a valuable addition to the existing library of organoboron dyes, offering fresh insights into the development of organic solid‐state lasers.. |
| 26. | Umamahesh Balijapalli, Ryo Nagata, Nishiki Yamada, Hajime Nakanotani, Masaki Tanaka, Anthony D'Aléo, Virginie Placide, Masashi Mamada, Youichi Tsuchiya, Chihaya Adachi, Highly Efficient Near‐Infrared Electrofluorescence from a Thermally Activated Delayed Fluorescence Molecule, Angewandte Chemie, 10.1002/ange.202016089, 133, 15, 8558-8563, 2021.04. |
| 27. | Yoshiaki Shoji, Yasuhiro Ikabata, Ivan Ryzhii, Rabia Ayub, Ouissam El Bakouri, Taiga Sato, Qi Wang, Tomoaki Miura, Buddhika S. B. Karunathilaka, Youichi Tsuchiya, Chihaya Adachi, Henrik Ottosson, Hiromi Nakai, Tadaaki Ikoma, Takanori Fukushima, An Element‐Substituted Cyclobutadiene Exhibiting High‐Energy Blue Phosphorescence, Angewandte Chemie, 10.1002/ange.202108413, 2021.07. |
| 28. | Masashi Mamada, Chihaya Adachi, Unexpected role of hole and electron blocking interlayers controlling charge carrier injection and transport in TADF based blue organic light-emitting diodes, Applied Physics Letters, 10.1063/5.0100373, 121, 13, 131103-131103, 2022.09, There has been increasing interest in blue organic light-emitting diodes based on thermally activated delayed fluorescence (TADF). The construction of a fully optimized device architecture is crucial in accordance with developing high-performance materials because highly efficient electroluminescence cannot be realized without balancing both carrier injection and transport with decreasing several exciton loss processes. Thus, the detailed mechanism of carrier injection, transport, and recombination in emitting layers has to be clarified. In this study, various device architectures for a recently emerged blue TADF molecular system based on multiple donors and acceptors were systematically investigated, especially by focusing on the interlayers. This work also aims to offer guidelines for improving device stabilities. Our findings clarify the role of each layer, providing in-depth insight into device design and the selection of proper materials for each constituted layer.. |
| 29. | Chin-Yiu Chan, Subeesh Madayanad Suresh, Yi-Ting Lee, Youichi Tsuchiya, Tomas Matulaitis, David Hall, Alexandra M. Z. Slawin, Stuart Warriner, David Beljonne, Yoann Olivier, Chihaya Adachi, Eli Zysman-Colman, Two boron atoms versus one: high-performance deep-blue multi-resonance thermally activated delayed fluorescence emitters, Chemical Communications, 10.1039/d2cc03347j, 58, 67, 9377-9380, 2022.07, Two new deep-blue narrowband multi-resonant emitters, 1B-DTACrs and 2B-DTACrs, one of which shows TADF, based on boron, nitrogen, and oxygen doped nanographenes are reported.. |
| 30. | Tatsuya Morofuji, Takuma Kurokawa, Youhei Chitose, Chihaya Adachi, Naokazu Kano, Trifluoromethylated thermally activated delayed fluorescence molecule as a versatile photocatalyst for electron-transfer- and energy-transfer-driven reactions, Organic & Biomolecular Chemistry, 10.1039/d2ob02055f, 20, 48, 9600-9603, 2022.11, Trifluoromethylated thermally activated delayed fluorescent molecule 4[Cz(CF3)2]IPN has been demonstrated as a versatile photocatalyst that facilitates radical reactions via electron transfer and dearomative cycloaddition via energy transfer.. |
| 31. | Emma V. Puttock, Chandana Sampath Kumara Ranasinghe, Mohammad Babazadeh, Jos C. M. Kistemaker, Junhyuk Jang, Mile Gao, David M. Huang, Chihaya Adachi, Paul L. Burn, Paul E. Shaw, Thermally activated delayed fluorescence poly(dendrimer)s – detrapping excitons for reverse intersystem crossing, Journal of Materials Chemistry C, 10.1039/d1tc05151b, 10, 20, 8109-8124, 2022.05, We compare the effect of donor strength on the optoelectronic properties of thermally activated delayed fluorescence poly(dendrimer)s and their dendrimer analogues.. |
| 32. | Yi‐Ting Lee, Chin‐Yiu Chan, Masaki Tanaka, Masashi Mamada, Kenichi Goushi, Xun Tang, Youichi Tsuchiya, Hajime Nakanotani, Chihaya Adachi, Tailor‐Made Multi‐Resonance Terminal Emitters toward Narrowband, High‐Efficiency, and Stable Hyperfluorescence Organic Light‐Emitting Diodes, Advanced Optical Materials, 10.1002/adom.202200682, 10, 17, 2200682-2200682, 2022.09. |
| 33. | Masaki Tanaka, Morgan Auffray, Hajime Nakanotani, Chihaya Adachi, Spontaneous formation of metastable orientation with well-organized permanent dipole moment in organic glassy films, Nature Materials, 10.1038/s41563-022-01265-7, 21, 7, 819-825, 2022.07. |
| 34. | Tomohiro Ryu, Kiyoshi Miyata, Masaki Saigo, Yuushi Shimoda, Youichi Tsuchiya, Hajime Nakanotani, Chihaya Adachi, Ken Onda, Solvent-dependent dual emission processes in charge-transfer excited states of phenothiazine-triphenyltriazine conformers, Chemical Physics Letters, 10.1016/j.cplett.2022.140155, 809, 140155-140155, 2022.12. |
| 35. | Shigetada Uemura, Susumu Oda, Masahiro Hayakawa, Ryosuke Kawasumi, Naoya Ikeda, Yi-Ting Lee, Chin-Yiu Chan, Youichi Tsuchiya, Chihaya Adachi, Takuji Hatakeyama, Sequential Multiple Borylation Toward an Ultrapure Green Thermally Activated Delayed Fluorescence Material, Journal of the American Chemical Society, 10.1021/jacs.2c10946, 145, 3, 1505-1511, 2022.12. |
| 36. | Jaehyun Bae, Mika Sakai, Youichi Tsuchiya, Naoki Ando, Xian-Kai Chen, Thanh Ba Nguyen, Chin-Yiu Chan, Yi-Ting Lee, Morgan Auffray, Hajime Nakanotani, Shigehiro Yamaguchi, Chihaya Adachi, Multiple resonance type thermally activated delayed fluorescence by dibenzo [1,4] azaborine derivatives, Frontiers in Chemistry, 10.3389/fchem.2022.990918, 10, 2022.09, We studied the photophysical and electroluminescent (EL) characteristics of a series of azaborine derivatives having a pair of boron and nitrogen aimed at the multi-resonance (MR) effect. The computational study with the STEOM-DLPNO-CCSD method clarified that the combination of a BN ring-fusion and a terminal carbazole enhanced the MR effect and spin-orbit coupling matrix element (SOCME), simultaneously. Also, we clarified that the second triplet excited state (T2) plays an important role in efficient MR-based thermally activated delayed fluorescence (TADF). Furthermore, we obtained a blue–violet OLED with an external EL quantum efficiency (EQE) of 9.1%, implying the presence of a pronounced nonradiative decay path from the lowest triplet excited state (T1).. |
| 37. | Shintaro Kohata, Hajime Nakanotani, Chihaya Adachi, Modulation of Intersystem Crossing Rate Induced by Singlet-triplet Energy Level Alignment in 1,2,3,5-Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene Single Crystals, Chemistry Letters, 10.1246/cl.220304, 51, 10, 989-992, 2022.10. |
| 38. | Samir Manna, Shunta Kakumachi, Kanak Kanti Das, Youichi Tsuchiya, Chihaya Adachi, Santanu Panda, Mechanistic dichotomy in the solvent dependent access to E vs. Z-allylic amines via decarboxylative vinylation of amino acids, Chemical Science, 10.1039/d2sc02090d, 13, 33, 9678-9684, 2022.07, A solvent-dependent access to E vs. Z-allylic amines was achieved via decarboxylative vinylation of amino acids. Detailed experimental studies have been conducted to understand the role of the solvent in the reactivity and stereoselectivity of the vinylation reactions.. |
| 39. | Rui Xu, Dingshuo Zhang, Junjie Si, Yihang Du, Qianqing Hu, Xiaoming Hao, Hong Zhao, Peiqing Cai, Qi Ai, Xin Yao, Yun Gao, Meiyi Zhu, Zenan Zhang, Muzhi Cai, Hin Wai Mo, Kentaro Harada, Zhizhen Ye, Xingliang Dai, Chihaya Adachi, Zugang Liu, Low-Voltage Driving Copper Iodide-Based Broadband Electroluminescence, ACS Energy Letters, 10.1021/acsenergylett.2c02471, 7, 12, 4408-4416, 2022.11. |
| 40. | Sahar Alasvand Yazdani, Amir Mikaeili, Fatima Bencheikh, Chihaya Adachi, Impact of excitonic and photonic loss mechanisms on the threshold and slope efficiency of organic semiconductor lasers, Japanese Journal of Applied Physics, 10.35848/1347-4065/ac759d, 61, 7, 074003-074003, 2022.07, Abstract We investigated the impact of various excitonic and photonic losses on the lasing threshold and slope efficiency of organic semiconductor lasers (OSLs) under optical and electrical excitations. The rate equations are solved numerically using the Euler method for an OSL and an organic semiconductor laser diode, including 4,4′-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) as a gain medium. The results showed that the loss mechanisms that affect the exciton and photon densities cause an increase in the laser threshold and a decrease in the slope efficiency. Further, we demonstrated that by using a thermally activated delayed fluorescence (TADF) emitter as a gain medium, the triplet excitons could be harvested by increasing the reverse intersystem crossing rate (kRISC), resulting in an appreciable decrease of the laser threshold and an increase of the slope efficiency. Accordingly, the TADF emitters with a fast kRISC are expected to significantly reduce the current density required for electrical excitation.. |
| 41. | Masashi Mamada, Hiroshi Katagiri, Chin‐Yiu Chan, Yi‐Ting Lee, Kenichi Goushi, Hajime Nakanotani, Takuji Hatakeyama, Chihaya Adachi, Highly Efficient Deep‐Blue Organic Light‐Emitting Diodes Based on Rational Molecular Design and Device Engineering, Advanced Functional Materials, 10.1002/adfm.202204352, 32, 32, 2204352-2204352, 2022.08. |
| 42. | Min Gyeong Choi, Chan Hee Lee, Chihaya Adachi, Sae Youn Lee, Highly Effective Thermally Activated Delayed Fluorescence Emitters Based on Symmetry and Asymmetry Nicotinonitrile Derivatives, Molecules, 10.3390/molecules27238274, 27, 23, 8274-8274, 2022.11, In this study, we developed two thermally activated delayed fluorescence (TADF) emitters, ICzCN and ICzCYP, to apply to organic light-emitting diodes (OLEDs). These emitters involve indolocarbazole (ICz) donor units and nicotinonitrile acceptor units with a twisted donor-acceptor-donor (D-A-D) structure for small singlet (S1) and triplet (T1) state energy gap (ΔEST) to enable efficient exciton transfer from the T1 to the S1 state. Depending on the position of the cyano-substituent, ICzCN has a symmetric structure by introducing donor units at the 3,5-position of isonicotinonitrile, and ICzCYP has an asymmetric structure by introducing donor units at the 2,6-position of nicotinonitrile. These emitters have different properties, such as the maximum luminance (Lmax) value. The Lmax of ICzCN reached over 10000 cd m−2. The external quantum efficiency (ηext) was 14.8% for ICzCN and 14.9% for ICzCYP, and both achieved a low turn-on voltage (Von) of less than 3.4 eV.. |
| 43. | Shi Tang, Petter Lundberg, Youichi Tsuchiya, Joan Ràfols‐Ribé, Yongfeng Liu, Jia Wang, Chihaya Adachi, Ludvig Edman, Efficient and Bright Blue Thermally Activated Delayed Fluorescence from Light‐Emitting Electrochemical Cells, Advanced Functional Materials, 10.1002/adfm.202205967, 32, 44, 2205967-2205967, 2022.08. |
| 44. | Ganbaatar Tumen-Ulzii, Morgan Auffray, Dino Klotz, George F. Harrington, Xian Kai Chen, Umamahesh Balijapalli, Veeramani Vediyappan, Nozomi Nakamura, Zhao Feng, Kotaro Takekuma, Yuki Fujita, Pangpang Wang, Sunao Yamada, Kaoru Tamada, Munkhbayar Batmunkh, Yu Lin Zhong, Fabrice Mathevet, Hayden Salway, Miguel Anaya, Samuel D. Stranks, Toshinori Matsushima, Chihaya Adachi, Defect Passivation by Pyridine-Carbazole Molecules for Efficient and Stable Perovskite Solar Cells, ACS Applied Energy Materials, 10.1021/acsaem.2c03364, 5, 12, 15819-15827, 2022.12, The defects in the light-harvesting perovskite absorber layer play a key role in limiting power conversion efficiencies (PCEs) and long-term stability of lead halide perovskite solar cells (PSCs). Although organic ammonium halides have been used for defect passivation in high-performance PSCs, the stability issue is still a challenge. Herein, we develop a novel material of pyridine-carbazole (Py-Cz) to passivate defects via coordination bonding. With this passivation, the photoluminescence intensity of perovskite films was increased. In addition, the formation of under-coordinated Pb2+defects in perovskite films was reduced significantly, enabling high-performance and long-term stable PSCs. Three different sets of PSCs were constructed, namely, without passivation, with phenethylammonium iodide (PEAI) (commonly used for passivation), and with Py-Cz passivation. Remarkably, the PSCs fabricated using the Py-Cz passivation not only achieved PCEs of over 20% but also retained 85% of their initial performances over more than 5000 h. In contrast, the PSCs without or with PEAI passivation degraded quickly during the long-term operational stability test under light illumination. This method opens up a new opportunity to develop highly efficient and operationally stable PSCs.. |
| 45. | Monirul Hasan, Atul Shukla, Masashi Mamada, Chihaya Adachi, Shih-Chun Lo, Ebinazar B. Namdas, Correlating Exciton Dynamics of Thermally Activated Delayed-Fluorescence Emitters to Efficiency Roll-Off in OLEDs, Physical Review Applied, 10.1103/physrevapplied.18.054082, 18, 5, 2022.11. |
| 46. | H. Park, S. Alasvand Yazdani, F. Bencheikh, R. Komatsu, S. Yokoyama, T. Kamiya, C. Adachi, Control of emission diffraction angles and laser threshold in mixed-order sampled distributed feedback laser with organic gain media, Journal of Applied Physics, 10.1063/5.0123476, 132, 20, 203101-203101, 2022.11, The control of laser emission angles in laser devices is essential for many optoelectronic and photonic applications such as optical sensing and displays. In this context, we studied the light diffraction pattern of laser beams in a one-dimensional sampled distributed feedback resonator having organic gain media. The gratings consist of the repetition of supercells having a mixed-order sampled grating in which 1st-order gratings surround a 2nd-order grating. The experimental results showed that the diffraction angles of the laser beams are quite diverse depending on the supercell structures. We demonstrate that the interval of the diffraction angle (θ) of the laser beams is inversely proportional to the length of the supercell experimentally and theoretically. By tuning the length of supercells as well as the length of 1st-order and 2nd-order regions, the interval θ was tuned from 0.1° to 43° with the different arc emission patterns. With the reduction of θ, i.e., the longer 1st-order region, a significant decrease in the laser threshold was obtained, resulting in the lowest lasing threshold of 2.5 ± 0.1 μJ/cm2 with ∼3.5 ns of a long pulse width excitation source.. |
| 47. | Chin-Yiu Chan, Yi-Ting Lee, Masashi Mamada, Kenichi Goushi, Youichi Tsuchiya, Hajime Nakanotani, Chihaya Adachi, Carbazole-2-carbonitrile as an acceptor in deep-blue thermally activated delayed fluorescence emitters for narrowing charge-transfer emissions, CHEMICAL SCIENCE, 10.1039/d2sc02478k, 13, 26, 7821-7828, 2022.07, This work reports a new acceptor for constructing donor-acceptor type (D-A type) blue thermally activated delayed fluorescence (TADF) emitters with narrowed charge-transfer (CT) emissions. A new acceptor core, carbazole-2-carbonitrile (CCN), is formed by the fusion of carbazole and benzonitrile. Three D-A type TADF emitters based on the CCN acceptor, namely 3CzCCN, 3MeCzCCN, and 3PhCzCCN, have been successfully synthesized and characterized. These emitters show deep-blue emissions from 439 to 457 nm with high photoluminescence quantum yields of up to 85% in degassed toluene solutions. Interestingly, all CCN-based deep-blue TADF emitters result in narrow CT emissions with full-width at half-maximums (FWHMs) of less than 50 nm in toluene solutions, which are pretty narrower compared with those of typical D-A type TADF emitters. Devices based on these emitters show high maximum external quantum efficiencies of up to 17.5%.. |
| 48. | Sahar Alasvand Yazdani, Fatima Bencheikh, Ryutaro Komatsu, Amir Mikaeili, Chihaya Adachi, Balanced electron and hole injection and transport in OLEDs by using transparent electrodes, Japanese Journal of Applied Physics, 10.35848/1347-4065/ac7e96, 61, 8, 088002-088002, 2022.07, Abstract In this study, electron and hole injection, and transport in semi-transparent organic light-emitting diodes, including dielectric/metal/dielectric (DMD) electrodes, were investigated. The DMD electrode was modified by incorporating a 5 nm-thick Cs:MoOx layer and a 10 nm-thick 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN) layer to improve the electron and hole injection in standard and inverse structures, respectively. The inverse structure showed a reasonably good and stable external quantum efficiency due to the well-balanced carrier densities at both low and high voltages which was confirmed by an electrical simulation study. Also, the peak position of the hole and electron recombination rate in the inverse structure was located on the ITO side, which is beneficial for reducing exciton quenching and photon absorption by metallic electrodes.. |
| 49. | Thanh Ba Nguyen, Hajime Nakanotani, Chihaya Adachi, An Overlooked Charge‐Transfer Interaction in the Interfacial Triplet–Triplet Upconversion Process in Blue Organic Light‐Emitting Diodes, Advanced Optical Materials, 10.1002/adom.202200704, 10, 18, 2200704-2200704, 2022.09. |
| 50. | Andrew Chapman, Elif Ertekin, Masanobu Kubota, Akihide Nagao, Kaila Bertsch, Arnaud Macadre, Toshihiro Tsuchiyama, Takuro Masamura, Setsuo Takaki, Ryosuke Komoda, Mohsen Dadfarnia, Brian Somerday, Alexander Tsekov Staykov, Joichi Sugimura, Yoshinori Sawae, Takehiro Morita, Hiroyoshi Tanaka, Kazuyuki Yagi, Vlad Niste, Prabakaran Saravanan, Shugo Onitsuka, Ki-Seok Yoon, Seiji Ogo, Toshinori Matsushima, Ganbaatar Tumen-Ulzii, Dino Klotz, Dinh Hoa Nguyen, George Harrington, Chihaya Adachi, Hiroshige Matsumoto, Leonard Kwati, Yukina Takahashi, Nuttavut Kosem, Tatsumi Ishihara, Miho Yamauchi, Bidyut Baran Saha, Md. Amirul Islam, Jin Miyawaki, Harish Sivasankaran, Masamichi Kohno, Shigenori Fujikawa, Roman Selyanchyn, Takeshi Tsuji, Yukihiro Higashi, Reiner Kirchheim, Petros Sofronis, Achieving a Carbon Neutral Future through Advanced Functional Materials and Technologies, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20210323, 95, 1, 73-103, 2022.01. |
| 51. | Masashi Mamada, Satoshi Maedera, Susumu Oda, Thanh Ba Nguyen, Hajime Nakanotani, Takuji Hatakeyama, Chihaya Adachi, A very low lasing threshold of DABNA derivatives with DFB structures, Materials Chemistry Frontiers, 10.1039/d2qm01040b, 7, 2, 259-266, 2022.11, A low lasing threshold of up to 0.27 μJ cm−1 was achieved by using TADF materials. Advanced light amplification architectures composed of dual DABNA derivatives were also demonstrated.. |
| 52. | Youichi Tsuchiya, Nozomi Nakamura, Shunta Kakumachi, Keiko Kusuhara, Chin-Yiu Chan, Chihaya Adachi, A convenient method to estimate the glass transition temperature of small organic semiconductor materials, Chemical Communications, 10.1039/d2cc01467j, 58, 80, 11292-11295, 2022.09, The convenient melt-blending method for DSC measurement provides the reliable glass transition temperature (Tg) of the materials which are hard to measure by the standard DSC measurement, e.g., organic semiconductors.. |
| 53. | Rossa Mac Ciarnáin, Hin Wai Mo, Kaori Nagayoshi, Hiroshi Fujimoto, Kentaro Harada, Robert Gehlhaar, Tung Huei Ke, Paul Heremans, Chihaya Adachi, A Thermally Activated Delayed Fluorescence Green OLED with 4500 h Lifetime and 20% External Quantum Efficiency by Optimizing the Emission Zone using a Single‐Emission Spectrum Technique, Advanced Materials, 10.1002/adma.202201409, 34, 29, 2201409-2201409, 2022.06. |
| 54. | Tony C Wu, Andrés Aguilar‐Granda, Kazuhiro Hotta, Sahar Alasvand Yazdani, Robert Pollice, Jenya Vestfrid, Han Hao, Cyrille Lavigne, Martin Seifrid, Nicholas Angello, Fatima Bencheikh, Jason E. Hein, Martin Burke, Chihaya Adachi, Alán Aspuru‐Guzik, A Materials Acceleration Platform for Organic Laser Discovery, Advanced Materials, 10.1002/adma.202207070, 35, 6, 2207070-2207070, 2022.12. |
| 55. | Xiao-Chun Fan, Kai Wang, Yi-Zhong Shi, Ying-Chun Cheng, Yi-Ting Lee, Jia Yu, Xian-Kai Chen, Chihaya Adachi, Xiao-Hong Zhang, Ultrapure green organic light-emitting diodes based on highly distorted fused π-conjugated molecular design, Nature Photonics, 10.1038/s41566-022-01106-8, 17, 3, 280-285, 2023.01. |
| 56. | Chun Li, Henrik Schopmans, Lukas Langer, Stefan Marschner, Abhinav Chandresh, Jochen Bürck, Youichi Tsuchiya, Adachi Chihaya, Wolfgang Wenzel, Stefan Bräse, Mariana Kozlowska, Lars Heinke, Twisting of Porphyrin by Assembly in a Metal‐Organic Framework yielding Chiral Photoconducting Films for Circularly‐Polarized‐Light Detection, Angewandte Chemie International Edition, 10.1002/anie.202217377, 62, 10, 2023.01. |
| 57. | Xun Tang, Chathuranganie A. M. Senevirathne, Toshinori Matsushima, Atula S. D. Sandanayaka, Chihaya Adachi, Progress and Perspective toward Continuous‐Wave Organic Solid‐State Lasers, Advanced Materials, 10.1002/adma.202211873, 2023.05. |
| 58. | Yitong Wang, Shigeki Mori, Hajime Nakanotani, Chihaya Adachi, Soji Shimizu, Post-Modification of Pyrrolopyrrole Aza-BODIPY toward High Near-Infrared Fluorescence Brightness, Organic Letters, 10.1021/acs.orglett.3c00848, 25, 17, 3040-3044, 2023.04. |
| 59. | Ayano Abe, Kenichi Goushi, Masashi Mamada, Chihaya Adachi, Organic Binary and Ternary Cocrystal Engineering Based on Halogen Bonding Aimed at Room‐Temperature Phosphorescence, Advanced Materials, 10.1002/adma.202211160, 2023.03. |
| 60. | Takahiko Yamanaka, Hajime Nakanotani, Katsuhiro Nakamoto, Chihaya Adachi, Electron Lifetime of Over One Month in Disordered Organic Solid‐State Films, Advanced Materials, 10.1002/adma.202210335, 35, 11, 2023.01. |
| 61. | Tomas Matulaitis, Paloma L. dos Santos, Youichi Tsuchiya, David B. Cordes, Alexandra M. Z. Slawin, Chihaya Adachi, Ifor D. W. Samuel, Eli Zysman‐Colman, Donor Influence on the Optoelectronic Properties of N‐Substituted Tetraphenylimidazole Derivatives, ChemistrySelect, 10.1002/slct.202300274, 8, 9, 2023.02. |
| 62. | Jian Haur Lee, Jing‐Xiang Huang, Chia‐Hsun Chen, Yi‐Ting Lee, Chin‐Yiu Chan, Yi‐Chung Dzeng, Po‐Wen Tang, Chi Chen, Chihaya Adachi, Tien‐Lung Chiu, Jiun‐Haw Lee, Chin‐Ti Chen, Classic Fluorophores With a Horizontal Alignment for Enhancing Light Outcoupling Efficiency (≈30%) and External Quantum Efficiency (≈7%) of Near Ultraviolet (λ max < 400 nm) Organic Light‐Emitting Diodes, Advanced Optical Materials, 10.1002/adom.202202666, 11, 8, 2023.02. |
| 63. | Zhao Feng, Xuelong Liu, Kentaro Imaoka, Tomohiro Ishii, Ganbaatar Tumen‐Ulzii, Xun Tang, George F. Harrington, Benoît Heinrich, Jean‐Charles Ribierre, Lise‐Marie Chamoreau, Lydia Sosa Vargas, David Kreher, Kenichi Goushi, Toshinori Matsushima, Guijiang Zhou, Fabrice Mathevet, Chihaya Adachi, Artificial p–n‐like Junction Based on Pure 2D Organic–Inorganic Halide Perovskite Structure Having Naphthalene Diimide Acceptor Moieties, Advanced Optical Materials, 10.1002/adom.202202734, 11, 10, 2023.03. |
| 64. | Lihua Chen, Chuanlong Li, Enguang Fu, Mengyang Li, Yoshiaki Kuboi, Zi-Ying Li, Zhenghong Chen, Jiaolong Chen, Xuelong Liu, Xun Tang, Lucas Frédéric, François Maurel, Chihaya Adachi, Fabrice Mathevet, Shaodong Zhang, A Donor–Acceptor Cage for Thermally Activated Delayed Fluorescence: toward a New Kind of TADF Exciplex Emitters, ACS Materials Letters, 10.1021/acsmaterialslett.3c00310, 5, 5, 1450-1455, 2023.04. |
| 65. | Yi Ting Lee, Po Chen Tseng, Takeshi Komino, Masashi Mamada, Jiun Haw Lee, Chihaya Adachi, Chao Tsen Chen, Chin Ti Chen, A chemical structure approach enhancing light outcoupling of dopant OLEDs and internal quantum efficiency of non-dopant OLEDs having bluish TADF emitters, Digest of Technical Papers - SID International Symposium, 10.1002/sdtp.12958, 50, Book 1, 470-473, 2019.05, Dopant and non-dopant OLEDs were fabricated for testing four TADF emitters, having EL of blue to greenish blue color. The tetraphenyibenzene (4Ph)-containing emitters have been demonstrated having a higher light outcoupling efficiency for dopant devices and a superior IQEfor the non-dopant devices.. |
| 66. | Masayuki Yahiro, Shun Sugawara, Shinichi Maeda, Yuko Shimoi, Pangpang Wang, Shin-ichiro Kobayashi, Kotaro Takekuma, Ganbaatar Tumen-Ulzii, Chuanjiang Qin, Toshinori Matsushima, Tadayuki Isaji, Yoshinori Kasai, Takashi Fujihara, Chihaya Adachi, Improved Performance of Perovskite Solar Cells by Suppressing the Energy-Level Shift of the PEDOT:PSS Hole Transport Layer, ACS Applied Energy Materials, 10.1021/acsaem.1c03213, 4, 12, 14590-14598, 2021.12. |
| 67. | A. Lennart Schleper, Kenichi Goushi, Christoph Bannwarth, Bastian Haehnle, Philipp J. Welscher, Chihaya Adachi, Alexander J. C. Kuehne, Hot exciplexes in U-shaped TADF molecules with emission from locally excited states, Nature Communications, 10.1038/s41467-021-26439-w, 12, 1, 2021.12, Abstract Fast emission and high color purity are essential characteristics of modern opto-electronic devices, such as organic light emitting diodes (OLEDs). These properties are currently not met by the latest generation of thermally activated delayed fluorescence (TADF) emitters. Here, we present an approach, called “hot exciplexes” that enables access to both attributes at the same time. Hot exciplexes are produced by coupling facing donor and acceptor moieties to an anthracene bridge, yielding an exciplex with large T1 to T2 spacing. The hot exciplex model is investigated using optical spectroscopy and quantum chemical simulations. Reverse intersystem crossing is found to occur preferentially from the T3 to the S1 state within only a few nanoseconds. Application and practicality of the model are shown by fabrication of organic light-emitting diodes with up to 32 % hot exciplex contribution and low efficiency roll-off.. |
| 68. | Kazuya Jinnai, Naohiro Nishimura, Chihaya Adachi, Ryota Kabe, Thermally activated processes in an organic long-persistent luminescence system, NANOSCALE, 10.1039/d0nr09227d, 13, 18, 8412-8417, 2021.05, Glow-in-the-dark materials can store absorbed photon energy and emit light for long periods of time. While inorganic long-persistent luminescence (LPL) materials are crystalline and often require rare metals, organic LPL (OLPL) materials are flexible and require no rare metals. The emission process of OLPL systems consists of photoinduced charge separation, charge accumulation, and emission from charge recombination. Although emission processes of OLPL systems have been investigated, the charge separation and accumulation processes remain enigmatic. In this study, we investigated the charge carrier dynamics of a binary OLPL system comprising of electron donors and acceptors. We confirmed the presence of thermal activation processes, thermally activated delayed fluorescence and thermoluminescence in the OLPL system.. |
| 69. | Umamahesh Balijapalli, Yi-Ting Lee, Buddhika S, B. Karunathilaka, Ganbaatar Tumen-Ulzii, Morgan Auffray, Youichi Tsuchiya, Hajime Nakanotani, Chihaya Adachi, Tetrabenzo[a,c]phenazine Backbone for Highly Efficient Orange–Red Thermally Activated Delayed Fluorescence with Completely Horizontal Molecular Orientation, Angewandte Chemie International Edition, 10.1002/anie.202106570, 60, 35, 19364-19373, 2021.06. |
| 70. | Tanguy Jousselin-Oba, Masashi Mamada, Karen Wright, Jérome Marrot, Chihaya Adachi, Abderrahim Yassar, Michel Frigoli, Synthesis, Aromaticity, and Application of peri-Pentacenopentacene: Localized Representation of Benzenoid Aromatic Compounds, 10.1002/anie.202112794, 61, 1, e202112794, 2021.11. |
| 71. | Chathuranganie A. M. Senevirathne, Seiya Yoshida, Morgan Auffray, Masayuki Yahiro, Buddhika S. B. Karunathilaka, Fatima Bencheikh, Kenichi Goushi, Atula S. D. Sandanayaka, Toshinori Matsushima, Chihaya Adachi, Recycling of Triplets into Singlets for High-Performance Organic Lasers, ADVANCED OPTICAL MATERIALS, 10.1002/adom.202101302, 2021.10, Achieving continuous-wave (CW) lasing in organic semiconductors is known to be a difficult task because long-lived triplets quench radiative singlets via singlet-triplet annihilation (STA). To avoid STA and operate organic lasers in CW or long-pulse photoexcitation, the triplets need to be removed from an organic laser gain medium. However, this triplet removal leads to a loss of excitons. In addition to removing the detrimental triplets, here it is reported a triplet recycling process, which includes triplet scavenging and successive triplet upconversion via triplet-triplet annihilation (TTA) to regenerate emissive singlet excitons in a laser medium. An anthracene derivative of 9-(1-naphthalenyl)-10-(4-(2-naphthalenyl)phenyl)anthracene (NaNaP-A) and a laser dye of 4,4 '-bis[4-(diphenylamino)styryl]biphenyl (BDAVBi) are used as the triplet recycling sensitizer and the emitting laser dye, respectively. In this laser system, NaNaP-A can efficiently scavenge the triplets formed on BDAVBi because the triplet level is deeper for NaNaP-A than for BDAVBi, and then NaNaP-A successively recycles the triplets into the BDAVBi's singlet state via TTA. The TTA compensates and overcomes the STA in this laser system. Hence, these laser devices can be operated with long pulse widths of up to 10 ms. This unique triplet recycling behavior is confirmed by transient photoluminescence (PL) and electroluminescence (EL) studies.. |
| 72. | Manabu Sakurai, Ryota Kabe, Masaaki Fuki, Zesen Lin, Kazuya Jinnai, Yasuhiro Kobori, Chihaya Adachi, Takashi Tachikawa, Organic photostimulated luminescence associated with persistent spin-correlated radical pairs, Communications Materials, 10.1038/s43246-021-00178-3, 2, 1, 2021.12, Abstract Photostimulated luminescence allows energy or data to be stored and released using electromagnetic waves as both the input and output, and has attracted considerable interest in the fields of biomedical and information technologies. However, this phenomenon is mostly limited to solid inorganic materials. Here, we report photostimulated luminescence from purely organic blend films, composed of electron donor, acceptor, and trap/emitter molecules. Charges in the films are accumulated as radical ions by ultraviolet light irradiation and then extracted by near-infrared light irradiation. Even after storage in the dark for one week they produce visible light with good repeatability, color tunability, and are responsive to weak external magnetic fields. These findings might broadly impact existing applications and provide new prospects for innovative flexible devices.. |
| 73. | Kazuya Jinnai, Ryota Kabe, Zesen Lin, Chihaya Adachi, Organic long-persistent luminescence stimulated by visible light in p-type systems based on organic photoredox catalyst dopants., Nature materials, 10.1038/s41563-021-01150-9, 21, 338-344, 2021.11, Organic long-persistent-luminescent (OLPL) materials demonstrating hour-long photoluminescence have practical advantages in applications owing to their flexible design and easy processability. However, the energy absorbed in these materials is typically stored in an intermediate charge-separated state that is unstable when exposed to oxygen, thus preventing persistent luminescence in air unless oxygen penetration is suppressed through crystallization. Moreover, OLPL materials usually require ultraviolet excitation. Here we overcome such limitations and demonstrate amorphous OLPL systems that can be excited by radiation up to 600 nm and exhibit persistent luminescence in air. By adding cationic photoredox catalysts as electron-accepting dopants in a neutral electron-donor host, stable charge-separated states are generated by hole diffusion in these blends. Furthermore, the addition of hole-trapping molecules extends the photoluminescence lifetime. By using a p-type host less reactive to oxygen and tuning the donor-acceptor energy gap, our amorphous blends exhibit persistent luminescence stimulated by visible light even in air, expanding the applicability of OLPL materials.. |
| 74. | Xiao-Chun Fan, Kai Wang, Yi-Zhong Shi, Jia-Xiong Chen, Feng Huang, Hui Wang, Ya-Nan Hu, Youichi Tsuchiya, Xue-Mei Ou, Jia Yu, Chihaya Adachi, Xiao-Hong Zhang, Managing Intersegmental Charge-Transfer and Multiple Resonance Alignments of D3-A Typed TADF Emitters for Red OLEDs with Improved Efficiency and Color Purity, Advanced Optical Materials, 10.1002/adom.202101789, 10, 3, 2101789, 2021.11. |
| 75. | Tomohiro Ishii, Kiyoshi Miyata, Masashi Mamada, Fatima Bencheikh, Fabrice Mathevet, Ken Onda, Stéphane Kéna-Cohen, Chihaya Adachi, Low-Threshold Exciton-Polariton Condensation via Fast Polariton Relaxation in Organic Microcavities, Advanced Optical Materials, 10.1002/adom.202102034, 10, 3, 2102034, 2021.11. |
| 76. | Shinichi Tan, Kazuya Jinnai, Ryota Kabe, Chihaya Adachi, Long-Persistent Luminescence from an Exciplex-Based Organic Light-Emitting Diode, ADVANCED MATERIALS, 10.1002/adma.202008844, 33, 23, 2021.06, Organic long-persistent luminescent systems (OLPLs) exhibiting long-lasting emission after photoexcitation consist of organic electron donors and acceptors, that are widely used in organic light-emitting diodes (OLEDs). Although OLPLs and OLEDs include very similar excitonic processes, long-lasting emission has never been observed in OLEDs. This study confirms the presence of long-persistent luminescence (LPL) under electrical excitation.. |
| 77. | Nicholle R. Wallwork, Masashi Mamada, Atul Shukla, Sarah K. M. McGregor, Chihaya Adachi, Ebinazar Namdas, Shih-Chun Lo, High-performance solution-processed red hyperfluorescent OLEDs based on cibalackrot, Journal of Materials Chemistry C, 10.1039/D1TC04937B, 10, 4767-4774, 2021.12. |
| 78. | Youichi Tsuchiya, Stefan Diesing, Fatima Bencheikh, Yoshimasa Wada, Paloma L. dos Santos, Hironori Kaji, Eli Zysman-Colman, Ifor D. W. Samuel, Chihaya Adachi, Exact Solution of Kinetic Analysis for Thermally Activated Delayed Fluorescence Materials, The Journal of Physical Chemistry A, 10.1021/acs.jpca.1c04056, 125, 36, 8074-8089, 2021.09. |
| 79. | Tomohiro Ishii, Fatima Bencheikh, Sébastien Forget, Sébastien Chénais, Benoît Heinrich, David Kreher, Lydia Sosa Vargas, Kiyoshi Miyata, Ken Onda, Takashi Fujihara, Stéphane Kéna‐Cohen, Fabrice Mathevet, Chihaya Adachi, Enhanced Light–Matter Interaction and Polariton Relaxation by the Control of Molecular Orientation, Advanced Optical Materials, 10.1002/adom.202101048, 2101048-2101048, 2021.09. |
| 80. | Xun Tang, Umamahesh Balijapalli, Daichi Okada, Buddhika S. B. Karunathilaka, Chathuranganie A. M. Senevirathne, Yi‐Ting Lee, Zhao Feng, Atula S. D. Sandanayaka, Toshinori Matsushima, Chihaya Adachi, Electron‐Affinity Substituent in 2,6‐Dicarbonitrile Diphenyl‐1λ 5 ‐Phosphinine (DCNP) Towards High‐Quality Organic Lasing and Electroluminescence under High Current Injection, Advanced Functional Materials, 10.1002/adfm.202104529, 2104529-2104529, 2021.08. |
| 81. | Brett Yurash, Alana Dixon, Carolina Espinoza, Alexander Mikhailovsky, Sangmin Chae, Hajime Nakanotani, Chihaya Adachi, Thuc-Quyen Nguyen, Efficiency of Thermally Activated Delayed Fluorescence Sensitized Triplet Upconversion Doubled in Three-Component System, Advanced Materials, 10.1002/adma.202103976, 34, 5, 2103976, 2021.11, As in many fields, the most exciting endeavors in photon upconversion research focus on increasing the efficiency (upconversion quantum yield) and performance (anti-Stokes shift) while diminishing the cost of production. In this vein, studies employing metal-free thermally activated delayed fluorescence (TADF) sensitizers have garnered increased interest. Here, for the first time, the strategy of ternary photon upconversion is utilized with the TADF sensitizer 2,4,5,6-tetrakis(carbazol-9-yl)isophthalonitrile (4CzIPN), resulting in a doubling of the upconversion quantum yield in comparison to the binary system employing p-terphenyl as the emitter. In this ternary blend, the sensitizer 4CzIPN is paired with an intermediate acceptor, 1-methylnaphthalene, in addition to the emitter molecule, p-terphenyl, yielding a normalized upconversion quantum yield of 7.6% while maintaining the 0.83 eV anti-Stokes shift. These results illustrate the potential benefits of utilizing this strategy of energy-funneling, previously used only with heavy-metal based sensitizers, to increase the performance of these photon upconversion systems.. |
| 82. | Yusuke Fukami, Masato Iwasawa, Masahiro Sasaki, Takuya Hosokai, Hajime Nakanotani, Chihaya Adachi, Keiki Fukumoto, Yoichi Yamada, Direct Observation of Photoexcited Electron Dynamics in Organic Solids Exhibiting Thermally Activated Delayed Fluorescence via Time-Resolved Photoelectron Emission Microscopy, Advanced Optical Materials, 10.1002/adom.202100619, 9, 19, 2100619, 2021.06, Solid-state films exhibiting thermally activated delayed fluorescence (TADF) can offer high internal electroluminescence (EL) quantum efficiency, even in a simplified device structure. However, the exciton dynamics in solid-state TADF films, particularly for the unexpected exciton loss processes such as concentration quenching, have not yet been clarified. The dynamics of photoexcited electrons in the TADF process of a 2,4,5,6-Tetra (9H-carbazol-9-yl) isophthalonitrile (4CzIPN) solid film are observed via time-resolved photoelectron emission microscopy (TR-PEEM) and the results are compared with the conventional time-resolved photoluminescence (TR-PL) technique. The initial decay process of the photoexcited electrons probed via TR-PEEM is thoroughly traced in the TR-PL signal, while unusual long-lived electrons are detected only through the use of TR-PEEM. These results indicate that the excitons of 4CzIPN spontaneously dissociate into free carriers within the exciton lifetime, which seems to be a common process that contributes to the exciton loss in polar organic solids.. |
| 83. | Yuanhui Sun, Bochen Liu, Yue Guo, Xi Chen, Yi-Ting Lee, Zhao Feng, Chihaya Adachi, Guijiang Zhou, Zhao Chen, Xiaolong Yang, Developing Efficient Dinuclear Pt(II) Complexes Based on the Triphenylamine Core for High-Efficiency Solution-Processed OLEDs, ACS Appl. Mater. Interfaces, 10.1021/acsami.1c06148, 13, 30, 36020-36032, 2021.07. |
| 84. | Jian Haur Lee, Hung-Yi Lin, Chia-Hsun Chen, Yi-Ting Lee, Tien-Lung Chiu, Jiun-Haw Lee, Chin-Ti Chen, Chihaya Adachi, Deep Blue Fluorescent Material with an Extremely High Ratio of Horizontal Orientation to Enhance Light Outcoupling Efficiency (44%) and External Quantum Efficiency in Doped and Non-Doped Organic Light-Emitting Diodes, ACS Appl. Mater. Interfaces, 10.1021/acsami.1c07859, 13, 29, 34605-34615, 2021.01. |
| 85. | Yi-Zhong Shi, Kai Wang, Shao-Li Zhang, Xiao-Chun Fan, Youichi Tsuchiya, Yi-Ting Lee, Gao-Le Dai, Jia-Xiong Chen, Cai-Jun Zheng, Shi-Yun Xiong, Xue-Mei Ou, Jia Yu, Jian-Sheng Jie, Chun-Sing Lee, Chihaya Adachi, Xiao-Hong Zhang, Characterizing the Conformational Distribution in an Amorphous Film of an Organic Emitter and Its Application in a “Self-Doping” Organic Light-Emitting Diode, Angewandte Chemie International Edition, 10.1002/anie.202108943, 60, 49, 25878-25883, 2021.09. |
| 86. | Masashi Mamada, Hajime Nakanotani, Chihaya Adachi, Amplified spontaneous emission from oligo(p-phenylenevinylene) derivatives, Materials Advances, 10.1039/D0MA00756K, 2, 3906-3914, 2021.04. |
| 87. | Buddhika S.B, KARUNATHILAKA, Umamahesh BALIJAPALLI, Toshinori MATSUSHIMA, Atula S.D. SANDANAYAKA, Chihaya ADACHI, Advanced Organic Laser System Having Triplet Scavengers, J-STAGE, 10.11370/isj.60.615, 60, 6, 615-630, 2021.12. |
| 88. | Li Zhao, DaeHyeon Kim, Jean‐Charles Ribierre, Takeshi Komino, Chihaya Adachi, Advanced Molecular Design for Organic Light Emitting Diode Emitters Based on Horizontal Molecular Orientation and Thermally Activated Delayed Fluorescence, Organic Semiconductors for Optoelectronics, 10.1002/9781119146131.ch12, 295-305, 2021.07. |
| 89. | Umamahesh Balijapalli, Xun Tang, Daichi Okada, Yi-Ting Lee, Buddhika S. B. Karunathilaka, Morgan Auffray, Ganbaatar Tumen-Ulzii, Youichi Tsuchiya, Atula S. D. Sandanayaka, Toshinori Matsushima, Hajime Nakanotani, Chihaya Adachi, 2,6-Dicarbonitrile Diphenyl-1 lambda(5)-Phosphinine (DCNP)-A Robust Conjugated Building Block for Multi-Functional Dyes Exhibiting Tunable Amplified Spontaneous Emission, ADVANCED OPTICAL MATERIALS, 10.1002/adom.202101122, 9, 21, 2021.11, Highly efficient organic light-emitting diodes (OLEDs) with the concurrent achievement of high external electroluminescence quantum efficiency (EQE) and low light amplification thresholds under optical excitation have been considered as a crucial evolution towards the development of high-performance electrically pumped organic semiconductor laser diodes. Herein, a series of 2,6-dicarbonitrile-diphenyl-1 lambda(5)-phosphinine (DCNP) based donor (D)-acceptor (A) type dyes with different electron-withdrawing and donating moieties have been designed and characterized. The well-manipulated D-A strength with tunable optical properties guaranteed the low amplified spontaneous emission (ASE) thresholds of below 10 mu J cm(-2) and furnished a wide-range color-tuning capability in the visible region (485-595 nm). Furthermore, employing a thermally-activated delayed fluorescence (TADF) molecule as a triplet harvester boosted the performance of OLEDs based on mDMCz that exhibits an exceptional EQE value of 18.4% which is an eightfold enhancement as compared with that of standard fluorescence OLEDs. Also, the TADF-assistant fluorescence (TAF) system enables a reduction of the ASE threshold to 3 mu J cm(-2) and excellent ASE stability. These results provide a rational design strategy to construct color-tunable lasing dyes with reduced ASE thresholds and clarify their potentiality as the fluorescent dopant in the TAF system to utilize up-converted triplet excitons via efficient energy transfer.. |
| 90. | Tanguy Jousselin-Oba, Masashi Mamada, Karen Wright, Jérome Marrot, Chihaya Adachi, Abderrahim Yassar, Michel Frigoli, Synthesis, crystal structure, tropicity and charge transport properties of diindenothienothiophene derivatives, Journal of Materials Chemistry C, 10.1039/D2TC01324J, 10, 7717-7723, 2022.04. |
| 91. | Yang-Kun Qu, Dong-Ying Zhou, Fan-Cheng Kong, Qi Zheng, Xun Tang, Yuan-Hao Zhu, Chen-Chao Huang, Zi-Qi Feng, Jian Fan, Chihaya Adachi, Liang-Sheng Liao, Zuo-Quan Jiang, Steric Modulation of Spiro Structure for Highly Efficient Multiple Resonance Emitters, Angewandte Chemie, 10.1002/anie.202201886, 61, 22, e202201886, 2022.01. |
| 92. | Takahiko Yamanaka, Hajime Nakanotani, Chihaya Adachi, Significant role of triplet spin state for exciton dissociation in organic solids, Science Advances, 10.1126/sciadv.abj9188, 8, 9, 2022.03, Clarification of the role of the spin state that initiates exciton dissociation is critical to attaining a fundamental understanding of the mechanism of organic photovoltaics. Although an excited spin-triplet state with an energy lower than that of excited spin-singlet state is disadvantageous in exciton dissociation, a small electron exchange integral results in small singlet-triplet energy splitting in some material systems. This energy splitting leads to a nearly isoenergetic alignment of both excited states, raising a question about the role of excited spin states in exciton dissociation. Herein, we show that the spin-triplet rather than the spin-singlet plays a critical role in the exciton dissociation that leads to the formation of free carriers. This result indicates that the spin-triplet inherently acts as an intermediate, leading to exciton dissociation. Thus, our demonstration provides a fundamental understanding of the role of excited spin states of organic molecular systems in photoinduced charge-carrier generation.. |
| 93. | Monirul Hasan, Siddhartha Saggar, Atul Shukla, Fatima Bencheikh, Jan Sobus, Sarah K. M. McGregor, Chihaya Adachi, Shih-Chun Lo, Ebinazar B. Namdas, Probing polaron-induced exciton quenching in TADF based organic light-emitting diodes, nature communications, 10.1038/s41467-021-27739-x, 13, 254, 2022.01. |
| 94. | Dinh Hoa Nguyen, Ganbaatar Tumen-Ulzii, Toshinori Matsushima, Chihaya Adachi, Performance Analysis of a Perovskite-Based Thing-to-Thing Optical Wireless Power Transfer System, IEEE Photonics Journal, 10.1109/JPHOT.2022.3146365, 14, 1, 2022.01. |
| 95. | Ayano Abe, Kenichi Goushi, Atula S.D. Sandanayaka, Ryutaro Komatsu, Takashi Fujihara, Masashi Mamada, Chihaya Adachi, Numerical Study of Triplet Dynamics in Organic Semiconductors Aimed for the Active Utilization of Triplets by TADF under Continuous-Wave Lasing, Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.1c03983, 13, 5, 1323-1329, 2022.02, The limitation of lasing duration less than nanosecond order has been a major problem for realizing organic solid-state continues-wave (CW) lasers and organic semiconductor laser diodes. Triplets accumulation under CW excitation has been well recognized as a critical inhibiting factor. To overcome this issue, the utilization of thermally activated delayed fluorescence (TADF) emitters is a promising mechanism because of efficient reverse intersystem crossing. Herein, we model the triplet accumulation processes under lasing and propose the active utilization of TADF for lasing based on our simulation analysis. We used the rate constants experimentally determined from the optical properties of a boron difluoride curcuminoid fluorophore showing both TADF and lasing. We demonstrate that the intersystem crossing efficiency is gradually increased after the convergence of relaxation oscillation, i.e., terminating laser oscillation. In addition, we found that when the reverse intersystem crossing rate is close to the intersystem crossing rate, CW lasing becomes dominant.. |
| 96. | Atul Shukla, Volter Entoma, Sarah K. M. McGregor, Monirul Hasan, Masashi Mamada, Evan G. Moore, Chihaya Adachi, Shih-Chun Lo, Ebinazar B. Namdas, Low Light Amplification Threshold and Reduced Efficiency Roll-Off in Thick Emissive Layer OLEDs from a Diketopyrrolopyrrole Derivative, Macromolecular Rapid Communications, 10.1002/marc.202200115, 2200115, 2022.03. |
| 97. | Toshinori Matsushima, Ryotaro Nasu, Kotaro Takekuma, Tomohiro Ishii, Zhao Feng, Xun Tang, Nozomi Nakamura, Ganbaatar Tumen-Ulzii, Chihaya Adachi, Efficient Perovskite Light-Emitting Diodes with a Siloxane-Blended Organic Hole Transport Layer, Advanced Photonics Research, 10.1002/adpr.202200003, 2200003, 2022.05. |
| 98. | Nicholle R. Wallwork, Masashi Mamada, Angus B. Keto, Sarah K. M. McGregor, Atul Shukla, Chihaya Adachi, Elizabeth Krenske, Ebinazar B. Namdas, Shih-Chun Lo, Cibalackrot Dendrimers for Hyperfluorescent Organic Light-Emitting Diodes, Macromolecular Rapid Communications, 10.1002/marc.202200118, 2200118, 2022.03. |
| 99. | Takuya Hosokai, Hiroyuki Matsuzaki, Hajime Nakanotani, Chihaya Adachi, Current understanding of mechanism of thermally activated delayed fluorescence: RISC beyond S-T energy gap, Proceedings of the International Display Workshops, 1, 690-693, 2017.01, © 2017 Proceedings of the International Display Workshops. All rights reserved. A mechanism of thermally activated delayed fluorescence (TADF) beyond the ordinary discussion of reverse intersystem crossing (RISC) determined by the energy gap between excited singlet (Si) and triplet (Ti) states is introduced. A new design strategy of highly efficient TADF materials will also be proposed.. |
| 100. | Takashi Kobayashi, Daisuke Kawase, Akitsugu Niwa, Atsumi Kayamyo, Takashi Nagase, Kenichi Goushi, Chihaya Adachi, Hiroyoshi Naito, Temperature dependence of the intersystem crossing rate in thermally activated delayed fluorescence emitters, 2019 COMPOUND SEMICONDUCTOR WEEK (CSW), 2019.05. |
| 101. | Katsuaki Suzuki, Shosei Kubo, Katsuyuki Shizu, Tatsuya Fukushima, Atsushi Wakamiya, Yasujiro Murata, Chihaya Adachi, Hironori Kaji, Triarylboron-Based Fluorescent Organic Light-Emitting Diodes with External Quantum Efficiencies Exceeding 20 %, Angewandte Chemie, 10.1002/ange.201508270, 127, 50, 15446-15450, 2015.12. |
| 102. | Harunobu Takeda, Cong Chen, Takeshi Komino, Hiroaki Yoshioka, Yuji Oki, Chihaya Adachi, THz Absorption Measurement and Calculation of Organic Thermally Activated Delayed Fluorescence Materials, 2017 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC), Part F82-CLEO_Europe 2017, 2017.06. |
| 103. | Ryoichi Ishimatsu, Eri Kunisawa, Koji Nakano, Chihaya Adachi, Toshihiko Imato, Electrogenerated Chemiluminescence and Electronic States of Several Organometallic Eu(III) and Tb(III) Complexes: Effects of the Ligands, ChemistrySelect, 10.1002/slct.201900595, 4, 9, 2815-2831, 2019.03, We report the electrochemical properties, and electrogenerated chemiluminescence (ECL) of eight different organometallic complexes of Eu(III) and Tb(III), Eu(dbm) phen, Eu(dbm) bath, Eu(fod) phen, Eu(tta) phen, Tb(acac) phen, Tb(acac) bath, Tb(fod) phen, and Tb(tmhd) bpy in acetonitrile, where phen, bath, and bpy are 1, 10-phenanthroline, bathophenanthroline, 2,2′-bipyridyl, respectively, and the anionic ligands, acac , dbm , fod , and tta are the enolate forms of acetylacetone, dibenzoylmethanate, 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, and thenoyltrifluoroacetone, respectively. The electronic states of the neutral and some charged states of the complexes were clarified with density functional theory calculations. The ECL spectra were recorded by using S O as a coreactant, and for all complexes, sharp ECL spectra, which are attributable to the f-f transitions, were observed. On the potential-dependent ECL spectra, broad ECLs, which were originated from the ligands, were also detected. Based on the ECL behavior and the electronic states, the mechanisms of the intraconfigurational ECL were discussed. 3 3 3 3 3 3 3 3 2 8 − − − − 2−. |
| 104. | Manabu Sakurai, Ryota Kabe, Masaaki Fuki, Zesen Lin, Kazuya Jinnai, Yasuhiro Kobori, Chihaya Adachi, Takashi Tachikawa, Organic Photostimulated Luminescence, 10.26434/chemrxiv.12956456, 2020.09, Photostimulated luminescence, which allows energy or data to be stored and released using electromagnetic waves as both the input and output, has attracted considerable interest in the fields of biomedical and informatics technologies, but this phenomenon is mostly limited to solid inorganic materials. Here, we report photostimulated luminescence from purely organic blend films composed of electron donor, acceptor, and trap/emitter molecules. In the films, charges are accumulated as radical ions by ultraviolet light irradiation and then extracted by near infrared light irradiation to produce visible light. Films are capable of multiple cycles (>10 times) of organic photostimulated luminescence, which was still observable from films left in the dark at room temperature for one week after excitation, and emission color could be varied by changing the trap/emitter molecules. These findings will broadly impact existing applications and provide new prospects for innovative flexible devices.. |
| 105. | Ru Feng, Narumi Sato, Mayuka Nomura, Akinori Saeki, Hajime Nakanotani, Chihaya Adachi, Takuma Yasuda, Hiroyuki Furuta, Soji Shimizu, Near-infrared absorbing pyrrolopyrrole aza-BODIPY-based donor-acceptor polymers with reasonable photoresponse, Journal of Materials Chemistry C, 10.1039/d0tc01487g, 8, 26, 8770-8776, 2020.07, © The Royal Society of Chemistry. Designing near-infrared (NIR) absorbing donor-acceptor (D-A) polymers with photoresponse beyond 900 nm has remained a challenge in the area of organic photovoltaics (OPV) owing to the limited kinds of strong electron acceptors. Here we present the use of pyrrolopyrrole aza-BODIPY (PPAB) as a new acceptor group in D-A polymers in place of a conventional diketopyrrolopyrrole acceptor to achieve power conversion efficiencies up to 2.27% despite the ultra-small bandgap of 1.08 eV. The small photon energy loss of the PPAB-based D-A polymer and moderately high short-circuit current of 8.52 mA cm-2 arising from the panchromatic visible/NIR absorption guarantee PPAB as a potential building block of D-A polymers for NIR photovoltaics. This journal is. |
| 106. | Katsuyuki Shizu, Chihaya Adachi, Hironori Kaji, Correlated Triplet Pair Formation Activated by Geometry Relaxation in Directly Linked Tetracene Dimer (5,5′-Bitetracene), ACS Omega, 10.1021/acsomega.0c04809, 6, 4, 2638-2643, 2020.11. |
| 107. | Inhae Zoh, Miyabi Imai-Imada, Jaehyun Bae, Hiroshi Imada, Youichi Tsuchiya, Chihaya Adachi, Yousoo Kim, Visualization of Frontier Molecular Orbital Separation of a Single Thermally Activated Delayed Fluorescence Emitter by STM, The Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.1c02140, 12, 31, 7512-7518, 2021.08. |
| 108. | Ganbaatar Tumen-Ulzii, Morgan Auffray, Toshinori Matsushima, Chihaya Adachi, Unintentional passivation of 4-tertbutyl pyridine for improved efficiency and decreased operational stability of perovskite solar cells, Applied Physics Letters, 10.1063/5.0051527, 118, 24, 241603-241603, 2021.06. |
| 109. | Dinh Hoa Nguyen, Toshinori Matsushima, Chuanjiang Qin, Chihaya Adachi, Toward Thing-to-Thing Optical Wireless Power Transfer: Metal Halide Perovskite Transceiver as an Enabler, Frontiers in Energy Research, 10.3389/fenrg.2021.679125, 9, 2021.06, This paper proposes a novel conceptual system of optical wireless power transfer (OWPT) between objects, which is different from the existing OWPT systems such that a single device—an optical transceiver—is employed. This optical transceiver, which is capable of both absorbing and emitting light, is fabricated from a metal halide perovskite known for its superior features that can help significantly reduce the whole system size and cost. The proposed system contributes to realizing a thing-to-thing OWPT network, in which surfaces of objects/things are covered by perovskite transceivers (fully or partially), enabling them to wirelessly charge or discharge from the others.. |
| 110. | Takaaki Miyazaki, Motonori Watanabe, Toshinori Matsushima, Ching-Ting Chien, Chihaya Adachi, Shih-Sheng Sun, Hiroyuki Furuta, Tahsin J. Chow, Heptacene: Synthesis and Its Hole-Transfer Property in Stable Thin Films, Chemistry – A European Journal, 10.1002/chem.202100936, 2021.04. |
| 111. | Yoshiaki Shoji, Yasuhiro Ikabata, Ivan Rhyzhii, Rabia Ayub, Ouissam El Bakouri, Taiga Sato, Qi Wang, Tomoaki Miura, Buddhika S. B. Karunathilaka, Youichi Tsuchiya, Chihaya Adachi, Henrik Ottosson, Hiromi Nakai, Tadaaki Ikoma, Takanori Fukushima, An Element‐Substituted Cyclobutadiene Exhibiting High‐Energy Blue Phosphorescence, Angewandte Chemie International Edition, 10.1002/anie.202106490, 60, 40, 21817-21823, 2021.06. |
| 112. | Yu Esaki, Masaki Tanaka, Toshinori Matsushima, Chihaya Adachi, Active Control of Spontaneous Orientation Polarization of Tris(8‐hydroxyquinolinato)aluminum (Alq 3 ) Films and Its Effect on Performance of Organic Light‐Emitting Diodes, Advanced Electronic Materials, 10.1002/aelm.202100486, 2100486-2100486, 2021.06. |
| 113. | C ADACHI, T TSUTSUI, S SAITO, ELECTROLUMINESCENT MECHANISM OF ORGANIC THIN-FILM DEVICES, ACTA POLYTECHNICA SCANDINAVICA-APPLIED PHYSICS SERIES, 170, 215-218, 1990.06. |
| 114. | T TSUTSUI, C ADACHI, S SAITO, BLUE ELECTROLUMINESCENCE IN ORGANIC MULTILAYER THIN-FILM DEVICES, ACTA POLYTECHNICA SCANDINAVICA-APPLIED PHYSICS SERIES, 170, 170, 145-148, 1990.06. |
| 115. | T TSUTSUI, C ADACHI, S SAITO, ELECTROLUMINESCENCE IN ORGANIC THIN-FILMS, PHOTOCHEMICAL PROCESSES IN ORGANIZED MOLECULAR SYSTEMS, 437-450, 1991.06. |
| 116. | T TSUTSUI, EI AMINAKA, Y HAMADA, C ADACHI, S SAITO, SIGNIFICANCE OF MULTILAYER STRUCTURES IN ORGANIC THIN-FILM ELECTROLUMINESCENT DEVICES, ELECTROLUMINESCENT MATERIALS, DEVICES, AND LARGE-SCREEN DISPLAYS, 1910, 180-189, 1993.08. |
| 117. | S SAITO, T TSUTSUI, M ERA, N TAKADA, C ADACHI, Y HAMADA, T WAKIMOTO, PROGRESS IN ORGANIC MULTILAYER ELECTROLUMINESCENT DEVICES, ELECTROLUMINESCENT MATERIALS, DEVICES, AND LARGE-SCREEN DISPLAYS, 1910, 212-221, 1993.08. |
| 118. | C Adachi, S Hibino, A Yamamori, M Uchida, T Koyama, Y Taniguchi, Organic light-emitting diodes using spherical aggregates, ORGANIC LIGHT-EMITTING MATERIALS AND DEVICES, 3148, 62-69, 1997.07, We have succeeded in fabricating submicrometer-sized organic light emitting diodes (OLED) with bright emission using a polymer blend. The cell structure was composed of ITO (indium-tin oxide)/hole transport layer (polymer blend layer)/emitter layer/MgAg. We used poly (methyl methacrylate) (PMMA) as an inert host material and N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine-polycarbonate (PC-TPD) as a guest material. The polymer blend layers showed various morphology depending on the concentration of PC-TPD. With 2wt% of PC-TPD, the PC-TPD formed submicrometer-sized spherical domains, actually prolate spheroids, in the PMMA. host layer. The domain diameters were around 200 nm according to AFM and SEM observations. The OLED including such a blend structure showed aggregation of bright submicrometer-sized electroluminescence spots. The number of working diodes exceeded four million per square centimeter.. |
| 119. | Toshiki Koyama, Makoto Murata, Shoji Yamaguchi, Chihaya Adachi, Yoshio Taniguchi, Specific Conductivity Dependence on Diameter of Submicro-Sized Polythiophene Fibrils, MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 10.1080/10587259808030204, 322, 85-90, 1998.04, Deposition mechanism and a diameter dependence of the conductivity of polythiophene derivative fibrils polymerized in pores of a membrane filter having submicrometer-sized pores aperture were discussed. Deposition process of the fibrils was able to be divided in the following three stages from SEM observation and polymerization current measurements. The first stage is the generation of deposition growth nucleus on the pore-inside wall and the filter surface, the second is growth of thickness of a thin-layer-deposit, and the third is the accumulation of a spherical deposit And, when the pore size became big, the second stage shortened remarkably, and thickness of the thin-layer-deposit became thinner, and the spherical deposition began earlier. From the simulated conductivity of the fibrils with each diameter, at the smaller pore aperture than a specific value, the thickness of the thin-layer-deposit having high-conductivity increases. When the pore aperture becomes smaller, the thin-layer-deposition is remarkably easy to occur.. |
| 120. | H Mochizuki, T Hasui, M Kawamoto, T Shiono, T Ikeda, C Adachi, Y Taniguchi, Y Shirota, Novel liquid-crystalline and amorphous materials containing oxadiazole and amine moieties for electroluminescent devices, CHEMICAL COMMUNICATIONS, 10.1039/b005550f, 19, 1923-1924, 2000.09, Three 1,3,4-oxadiazole derivatives with an amine and an alkyl tail were designed and synthesized as novel electroluminescent materials; it was found that the length of alkyl tail and the structure of the amine strongly affect the phase structure of the oxadiazole derivatives.. |
| 121. | ME Thompson, S Lamansky, P Djurovich, D Murphy, F Abdel-Razzaq, Forrest, SR, M Baldo, PE Burrows, C Adachi, L Michalski, K Rajan, JJ Brown, High efficiency organic electrophosphorescent devices, ORGANIC LIGHT-EMITTING MATERIALS AND DEVICES IV, 4105, 119-124, 2000.06, We have fabricated saturated red, orange, yellow and green OLEDs, utilizing phosphorescent dopants. Using phosphorescence based emitters we have eliminated the inherent 25% upper limit on emission observed for traditional fluorescence based systems. The quantum efficiencies of these devices are quite good, with measured external efficiencies > 15% and > 40 lum/W (green) in the best devices. The phosphorescent dopants in these devices are heavy metal containing molecules (i.e. Pt, and Ir), prepared as both metalloporphyrins and organometallic complexes. The high level of spin orbit coupling in these metal complexes gives efficient emission from triplet states. In addition to emission from the heavy metal dopant, it is possible to transfer the exciton energy to a fluorescent dye, by Forster energy transfer. The heavy metal dopant in this case acts as a sensitizer, utilizing both singlet and triplet excitons to efficiently pump a fluorescent dye. We discuss the important parameters in designing electrophosphorescent OLEDs as well as their strengths and limitations. Accelerated aging studies, on packaged devices, have shown that phosphorescence based OLEDs can have very long device lifetimes.. |
| 122. | R Naitou, M Ichikawa, T Suzuki, C Adachi, T Koyama, Y Taniguchi, Energy relay systems for efficient organic light-emitting devices: Influence of formation of exciplex as revealed by photoexcitation, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 370, 31-34, 2001.09, We investigated potential of performance enhancement for organic light-emitting diodes (OLEDs) by an energy relay system through exciplex Formed between a hole transport material (HTM) and an electron transport material (ETM) as revealed by photoexcitation. An enhancement of a dopant (Coumarin 6) emission occurred depending on combination of HTM and ETM, and the dependency can be explained by an overlap integral between an exciplex emission and an absorption of Coumarin 6 as a dopant. Possibility of performance enhancement by the energy relay system was suggested experimentally.. |
| 123. | Hirotaka Mochizuki, T. Hasui, Osamu Tsutsumi, Akihiko Kanazawa, Takeshi Shiono, Tomiki Ikeda, Chihaya Adachi, Y. Taniguchi, Y. Shirota, Electroluminescent Behavior of Oxadiazole Derivatives in Liquid-Crystalline Media, Mol. Cryst. Liq. Cryst., 365, 129-138, 2001.01. |
| 124. | Adamovich, V, J Brooks, A Tamayo, AM Alexander, PI Djurovich, BW D'Andrade, C Adachi, Forrest, SR, ME Thompson, High efficiency single dopant white electrophosphorescent light emitting diodes, NEW JOURNAL OF CHEMISTRY, 10.1039/b204301g, 26, 9, 1171-1178, 2002.08, Efficient white electrophosphorescence has been achieved with a single emissive dopant. The dopant in these white organic light emitting diodes (WOLEDs) emits simultaneously from monomer and aggregate states, leading to a broad spectrum and high quality white emission. The dopant molecules are based on a series of platinum(II) [2-(4,6-difluorophenyl)pyridinato-N,C-2'] beta-diketonates. All of the dopant complexes described herein have identical photophysics in dilute solution with structured blue monomer emission (lambda(max) = 468, 500, 540 nm). A broad orange aggregate emission ( l 580 nm) is also observed, when doped into OLED host materials. The intensity of the orange band increases relative to the blue monomer emission, as the doping level is increased. The ratio of monomer to aggregate emission can be controlled by the doping concentration, the degree of steric bulk on the dopant and by the choice of the host material. A doping concentration for which the monomer and excimer bands are approximately equal gives an emission spectrum closest to standard white illumination sources. WOLEDs have been fabricated with doped CBP and mCP luminescent layers (CBP = N,N'-dicarbazolyl-4,4'-biphenyl, mCP = N,N'-dicarbazolyl-3,5-benzene). The best efficiencies and color stabilities were achieved when an electron/exciton blocking layer (EBL) is inserted into the structure, between the hole transporting layer and doped CBP or mCP layer. The material used for an EBL in these devices was fac-tris(1-phenylpyrazolato-N,C-2')iridium(III). The EBL material effectively prevents electrons and excitons from passing through the emissive layer into the hole transporting NPD layer. CBP based devices gave a peak external quantum efficiency of 3.3 +/- 0.3% (7.3 +/- 0.7 lm W-1) at 1 cd m(-2), and 2.3 +/- 0.2% (5.2 +/- 0.3 lm W-1) at 500 cd m(-2). mCP based devices gave a peak external quantum efficiency of 6.4% (12.2 lm W-1, 17.0 cd A(-1)), CIE coordinates of 0.36, 0.44 and a CRI of 67 at 1 cd m(-2) (CIE = Commission Internationale de l'Eclairage, CRI = color rendering index). The efficiency of the mCP based device drops to 4.3 +/- 0.5% (8.1 +/- 0.6 lm W-1, 11.3 cd A(-1)) at 500 cd m(-2), however, the CIE coordinates and CRI remain unchanged.. |
| 125. | Yoshiro Sato, Kenichi Goushi, Hiroyuki Sasabe, Chihaya Adachi, Kenichi Goushi, Hiroyuki Sasabe, Masami Saito, Chihaya Adachi, Julie J. Brown, High Efficiency White Electrophosphorescence Mechanism with Two Phosphorescent Dopants, The transactions of the Institute of Electrical Engineers of Japan.A, 10.1541/ieejfms.124.414, 124, 5, 414-420, 2004.08, High efficiency white organic light emitting diodes (WOLED) have been expected for applications of lighting, illumination and back-light sources for LCD. Recently, since organic phosphors demonstrated very high electroluminescence (EL) quantum efficiency of ∼100%, high efficiency WOLED with the organic phosphors has been anticipated. In this study, we employed an emitter layer which is doped with blue and red phosphorescence molecules. In our optimized device structure, we obtained maximum EL quantum efficiency of 4%. However, the shapes of the EL spectrum were strongly dependent on current density. With analysis of exciton decay process under optical and electrical excitations, we conclude that triplet-triplet annihilation occurs in blue and red phosphors independently, resulted in a significant change of the EL spectrum. Thus, the coincidence of the lifetimes of the blue and red phosphors is indispensable to escape change of EL spectrum with current density. © 2004, The Institute of Electrical Engineers of Japan. All rights reserved.. |
| 126. | Y Kawamura, K Goushi, J Brooks, JJ Brown, H Sasabe, C Adachi, Phosphorescence quantum efficiency and intermolecular interaction of Iridium(III) complexes in co-deposited films with organic semiconducting hosts, Organic and Nanocomposite Optical Materials, 846, 73-78, 2005.08, We accurately measured the absolute photoluminescence (PL) quantum efficiency (eta(PL)) Of organic solid-state thin films by using an integrating sphere. We measured the eta(PL) Of conventional organic materials used in organic light emitting diodes, such as a tris (8-quinolionolato)aluminum(III) complex (Alq(3)), and a phosphorescent 1.5mol%-fac-tris(2-phenylpyridyl)iridium(III):4,4'-bis(carbazol-9-yl)-2,2'-biphenyl [Ir(ppy)(3):CBP] co-deposited film. Alq(3) and lr(ppy)(3):CBP showed a eta(PL) = 20 +/- 1% and 97 +/- 2%, which corresponded well to external electroluminescence efficiency using these materials. We also measured red emitting bis[2-(2'-benzothienyl)pyridinato-N,C-3'] (acetylacetonato) iridium(III) [BtP(2)Ir(acac)] with CBP, and the blue complex, bis[(4,6-difluorophenyl)pyridinato -N, C-2](picolinato)iridium(III)[FIrpic], with m-bis(N-carbazolyl)benzene. The maximum eta(PL) values for BtP(2)Ir(acac), and FIrpic were 51 +/- 1 % (at 1.4mol%), and 99 +/- 1% (1.2mol%), respectively. These results suggest that the TIEL of red phosphorescent OLEDs using BtP(2)Ir(acac) as the dopant can be as high as 10%, and blue devices using FIrpic can reach the theoretical limit of 20%.. |
| 127. | K Goushi, H Sasabe, C Adachi, Phosphorescence decay mechanism of Ir(ppy)(3) in a solid matrix, JOURNAL OF PHOTOPOLYMER SCIENCE AND TECHNOLOGY, 10.2494/photopolymer.18.47, 18, 1, 47-50, 2005.07, The phosphorescence intensities of the green phosphor fac tris(2-phenylpyridine) iridium [Ir(ppy)(3)] in a polymethylmethacrylate [PMMA] host matrix are independent of temperature, while the phosphorescence lifetimes increase significantly at temperatures below T similar to 50 K. In this paper, we propose a phosphorescence decay mechanism for Ir(ppy)(3) to rationalize the characteristic temperature dependence of the transient phosphorescence. By comparing a numerical model with the experimental data, we demonstrate that mutual energy transfer between the sub-levels of triplet states can explain the characteristic temperature dependence.. |
| 128. | Takahito Oyamada, Hiroyuki Uchiuzo, Noriyuki Shimoji, Kazumi Matsushige, Hiroyuki Sasabe, Chihaya Adachi, Organic light-emitting transistors, IDMC 05: PROCEEDINGS OF THE INTERNATIONAL DISPLAY MANUFACTURING CONFERENCE 2005, 269-270, 2005.02, We succeeded in observing electroluminescence (EL) of Tetraphenulpyrene (TPPy) as an active layer in an organic field-effect transitor (OFET). In particular, an OFET with a short channel of dSD<1.0 mu m demonstrated higher EL efficiency than one with a much longer channel (dSD<10 mu m). We observed a maximum EL quantum efficiency (nmax) of similar to 0.3% in the short-channel-length device at an applied source-drain voltage of Vd similar to 100 V and a gate voltage of Vg > -50 V. From the OFET characteristics, although the TPPy layer demonstrated typical p-type operation, the occurence of EL clearly indicated simultaneous hole and electron injection from the source and drain electronics, respectively under high Vd and Vg.. |
| 129. | Chihaya Adachi, Takahito Oyamada, Organic light-emitting transistor - Fundamental characteristics and applications, IDW/AD '05: PROCEEDINGS OF THE 12TH INTERNATIONAL DISPLAY WORKSHOPS IN CONJUNCTION WITH ASIA DISPLAY 2005, VOLS 1 AND 2, 1033-1036, 2005.12, We succeeded in observing bright electroluminescence (EL) from 1wt%-rubrene doped tetraphenylpyrene (TPPy) as an active layer in an organic field-effect transistor (OFET) structure. We observed a maximum EL quantum efficiency (eta(ext)) of similar to 0.5 % with a Cr/Au source-drain electrode. From the OFET characteristics, although the 1wt%-rubrene:TPPy co-deposited layer demonstrated typical p-type operation, the occurrence of EL clearly indicated occurrence of simultaneous hole and electron injections from the source and drain electrodes, respectively. This device configuration provides novel organic light emitting diode structure where anode (source) and cathode (drain) electrodes are laterally arranged, giving us a chance to control drain current by changing gate bias.. |
| 130. | Hajime Nakanotani, Hiroyuki Sasabe, Chihaya Adachi, Low lasing threshold in organic distributed feedback solid state lasers using bisstyrylbenzene derivative as active material, Proceedings of SPIE - The International Society for Optical Engineering, 10.1117/12.629383, 5937, 1-7, 2005.12, We demonstrate very low threshold laser oscillation (Eth= 0.78 ±0.5 μJ/cm2) from an organic semiconductor thin film employing 2,5-bis(p-(N-phenyl-N-(m-tolyl)amino)styryl)benzene (BSB-Me) as an active gain medium equipped with a second order distributed feedback resonator. Further, we demonstrate laser oscillation under optical excitation from an organic light emitting device equipped with transparent ITO hole and electron injection electrodes. In addition, we demonstrate injection and transport of high current density over J > 500 A/cm2 in an organic light emitting diode using highly thermal conductive substrates and a small electrode under short pulse voltage excitation.. |
| 131. | O Karthaus, C Adachi, S Arakaki, A Endo, T Wada, Dewetting-induced self-organisation of nano-and microstructures for optoelectronic applications, Smart Materials III, 10.1117/12.581911, 5648, 251-255, 2005.05, A dewetting process of an evaporating solution is used to form micrometer-sized amorphous droplets, or domes, of the low molar mass solute on substrates such as silicon, mica, glass, and indium-tin-oxide. Using dewetting, the organic hole transporting material of organic light emitting diodes was patterened into micrometer-sized domes on an indium-tinoxide electrode. Annealing led to a structural change of the domes, which was investigated by optical and electron microscopies. The dewetted dome samples were then coated with electron transport material and top electrode to give functioning organic light emitting diodes. Microscope imaging reveals a strong luminescence from the micrometer-sized domes.. |
| 132. | Kenichi Goushi, Jason Brooks, Julie J. Brown, Hiroyuki Sasabe, Chihaya Adachi, Spin-relaxation process of excited triplet states of Ir(ppy)(3), JOURNAL OF PHOTOPOLYMER SCIENCE AND TECHNOLOGY, 10.2494/photopolymer.19.181, 19, 2, 181-186, 2006.08, The phosphorescence intensities of the green phosphor, fac tris(2-phenylpyridine) iridium [Ir(ppy)(3)], in a polymethylmethacrylate [PMMA] host matrix are independent of temperature, while the phosphorescence lifetimes increase significantly at temperatures below T similar to 50 K. In this paper, to rationalize the characteristic temperature dependence of the transient phosphorescence of Ir(ppy)(3), we propose a model where the triplet excited states split by spin-orbital interaction, forming three levels in which mutual energy transfer between the sub-levels of triplet states occurs. We discuss the validity of this numerical model by comparing with the experimental result of the transient phosphorescence in a PMMA host matrix and demonstrate that the model well explains the characteristic temperature dependence.. |
| 133. | O Karthaus, C Adachi, S Arakaki, A Endo, T Wada, Preparation of micropatterned organic light emitting diodes by self-organization, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 10.1080/15421400500365227, 444, 87-94, 2006.02, A dewetting process of an evaporating solution is used to form micrometer-sized amorphous droplets, or domes, of the low molar mass solute on substrates such as silicon, mica, glass, and indium-tin-oxide. Using dewetting, the organic hole transporting material of organic light emitting diodes was patterened into micrometer-sized domes on an indium-tin-oxide electrode. Annealing led to a structural change of the domes, which was investigated by optical and electron microscopes. The dewetted dome samples were then coated with electron transport material and top electrode to give functioning organic light emitting diodes devices.. |
| 134. | Shinya Furusake, Sumio Maruyama, Hiroyuki Sasabe, Chihaya Adachi, Photoluminescence characteristics of dendrimers containing (tris(8-hydroxyquinoline)aluminum) as a core unit, KOBUNSHI RONBUNSHU, 10.1295/koron.63.675, 63, 10, 675-680, 2006.10, We report on photoluminescence (PL) characteristics of dendrimers having (tris (8-hydroxy quinoline)aluminum) (Alq(3)) as a core unit. Although Alq3 derivatives are generally insoluble, the dendrimers were soluble in conventional organic solvents due to the presence of bulky dendron. We measured the transient PL and absolute PL efficiency of the dendrimers, dendron and AlClq(3) (core unit), and we clarified the location of pi-conjugation, which is an origin of PL. The PL characteristics indicated that pi-conjugation in the dendrimers is localized between a dendron and a quinoline ligand. Although the PL efficiencies are Phi(PL) = 20-40% in their solid films, the EL efficiencies are limited to Phi(EL) similar to 10(-2)%.. |
| 135. | Ayataka Endo, Jason Brooks, Julie J. Brown, Hiroyuki Sasabe, Chihaya Adachi, Organic blue electrophosphorescence using a cyclic siloxane compound as a host material, KOBUNSHI RONBUNSHU, 10.1295/koron.63.686, 63, 10, 686-690, 2006.09, In organic blue electrophosphorescence diodes, we used hexaphenylcyclotrisiloxane (DPSiO3) as a host material aiming for high efficiency blue electroluminescence (EL). The phosphorescence spectrum of the siloxane compound was measured at T = 77 K in an EPA solution and the results well coincided with those of a benzene solution, indicating that the pi-conjugation of DPSiO3 is basically localized in a benzene ring. In the OLED devices with DPSiO3 as a host, the maximum external EL efficiency of eta(ext) = 11.1% was obtained with iridium (III) bis (4,6-di-fluorophenyl)-pyridinato-N, C-2) picolinate (FIrpic) as an emitter.. |
| 136. | Y. Oku, N. Shimoji, T. Tanabe, S. Akiyama, T. Oyamada, H. Uchiuzou, C. Adachi, K. Matsushige, Novel active-matrix panel with organic light emitting field effect transistor, IDW '06: PROCEEDINGS OF THE 13TH INTERNATIONAL DISPLAY WORKSHOPS, VOLS 1-3, 667-+, 2006.06, We successfully demonstrated a novel active-matrix panel having an organic light-emitting field-effect transistor (OLEFET) on a Si substrate. An OLEFET, a switching transistor, and a capacitor were integrated into each pixel. As an OLEFET material, tetraphenylpyrene (TPPy) doped with rubrene at 1wt% was employed. The switching transistor was fabricated with pentacene. All organic transistors are bottom-contact-type, using conventional photolithography. An W display panel clearly showed moving characters.. |
| 137. | Toshinori Matsushima, Chihaya Adachi, Injection of current densities over kA/cm(2) in organic thin films and investigation of charge-carrier transport mechanisms in current density region between nA/cm(2) and kA/cm(2), ORGANIC LIGHT EMITTING MATERIALS AND DEVICES X, 10.1117/12.682122, 6333, 2006.12, We investigate current density-voltage (J-V) characteristics of copper plithalocyanine thin-film devices, with active areas ranging from S = 1,000,000 to 7.9 mu m(2), and analyze their charge-carrier transport mechanisms under current densities between nA/cm(2) and kA/cm(2). We demonstrate injection of 128 kA/cm(2) in the smallest device having S = 7.9 tM2. Furthermore, we find that J-V characteristics are divided into three regions between nA/cm(2) and kA/cm(2) : ohm current, shallow-trap space-charge-limited current (SCLC), and trap-free SCLC. In a shallow-trap SCLC region, we observe a large shift in J-V characteristics depending upon the active areas. From analyses of carrier traps with a thermally stimulated current (TSC) measurement, we see that TSC signal intensities of these films decrease as the active area is reduced. Hence, we conclude that a large shift in J-V characteristics is attributable to the change of carrier trap concentrations in these films.. |
| 138. | Chihaya Adachi, Toshinori Matsushima, Hajime Nakanotani, Tomo Sakanoue, Masayuki Yahiro, Daisuke Yokoyama, Frontier of organic light emitting devices, PROCEEDINGS OF THE 2007 INTERNATIONAL WORKSHOP ON THE PHYSICS OF SEMICONDUCTOR DEVICES: IWPSD-2007, 10.1109/IWPSD.2007.4472568, 534-538, 2007.12, We report recent progresses on organic light emitting devices such as organic light emitting diode (OLED), light-emitting organic field effect transistor (LE-OFET) and organic laser diode (OLD). We demonstrate very low driving voltage of OLEDs using a p-i-n structure which also provides high current carrier injection over kA/cm(2). Further we demonstrate novel organic devices such as light emitting FET. We also discuss future prospect of OLD based on our recent materials' development and analysis of operation mechanism.. |
| 139. | Larisa Fenenko, C. Adachi, Yoichiro Nakanishi, Petro Smertenko, Sergey Svechnikov, Features of conductivity and electroluminescence of new poly (9,9-dioctylfluorenyl-2,7-diyl) - End capped with polyhedral oligomeric silsesquioxanes, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 10.1080/15421400701224678, 467, 303-309, 2007.09, The emission and conductivity of anew polymerpoly (9,9-dioctylfluorenyl-2,7-diyl) end capped with polyhedral oligomeric silsesquioxanes (PFO-POSS) have been investigated by the differential approach. Thin films of PFO-POSS showed pure blue photoluminescence (PL) with structured spectrum and a maximum at lambda(PL) = 423 nm. However, the OLED structures formed on the PFO-POSS base emitted green light with broadened spectrum and a maximum at)lambda(EL) = 510 similar to 529 nm. The electroconductivity and electroluminescence have shown that the greatest influence on the current voltage and luminance current characteristics is rendered by introducing the electron transport layer to the multilayer OLED structure under investigation.. |
| 140. | Kyung Soo Son, Masayuki Yahiro, Toshiro Imai, Hiroki Yoshizaki, Chihaya Adachi, Blue organic electrophosphorescence diodes using diarylamino-substituted heterocyclic compounds as host material, JOURNAL OF PHOTOPOLYMER SCIENCE AND TECHNOLOGY, 10.2494/photopolymer.20.47, 20, 1, 47-51, 2007.01, Diarylamino-substituted heterocyclic compounds (DHCs), 2,6-dicarbazolo-1,5-pyridine (PYD2) and 2,4,6-tricarbazolo-1,3,5-pyrimidine, (PYM3), possess a high triplet energy level (T-1) of T-1= 2.93 eV (PYD2) and T-1= 2.89 eV (PYM3), respectively, in their solid state films. 6wt%-Iridium(III)bis[(4,6-di-fluorophenyl)-pyridinato-N,C-2]picolinate (Flrpic):PYD2- and 6wt%-FIrpic:PYM3-doped films showed high photoluminescence (PL) efficiencies of Phi(PL) = 88 +/- 2 % and Phi(PL)= 80 +/- 1 %, indicating near perfect confinement of FIrpic triplet excitons. By increasing the FIrpic concentration in DHC hosts, lower driving voltage and higher external electroluminescence (EL) quantum efficiencies (eta(EL)) were observed, indicating enhancement of electron injection and transport (electron current) in these emitting layers.. |
| 141. | Ayataka Endo, Mai Ogasawara, Atsushi Takahashi, Yoshimine Kato, Chihaya Adachi, Thermally Activated Delayed Fluorescence (TADF) from Sn4(+)-porphyrin Complexes and Their Application to Organic Light Emitting Diodes - Novel Pathway for High Efficiency Electroluminescence, 28TH INTERNATIONAL DISPLAY RESEARCH CONFERENCE, 23-25, 2008.12, We developed six Sn4(+)-porphyrin complexes showing thermally activated delayed fluorescence (TADF). The TADF intensities were increased with an increase of temperature owing to acceleration of the reverse intersystem crossing from triplet to singlet excited states by heat activation. Further, we demonstrate TADF under electrical excitation. We believe that TADF will provide novel light-emitting mechanism which significantly enhances electroluminescence quantum efficiency.. |
| 142. | Chihaya Adachi, Toshinori Matsushima, Hajime Nakanotani, Daisuke Yokoyama, Masayuki Yahiro, Organic light emitting devices from OLED to organic laser diode, AOE 2007: ASIA OPTICAL FIBER COMMUNICATION & OPTOELECTRONIC EXPOSITION & CONFERENCE, CONFERENCE PROCEEDINGS, 10.1109/AOE.2007.4410748, 189-+, 2008.10, We mention some significant progresses on organic light emitting diode (OLED), organic laser diode (OLD) and organic field effect transistor (OFET). We discuss prospect of OLD based on recent developments of organic light emitting devices.. |
| 143. | Chihaya Adachi, Invited paper: Molecular design of organic semiconductors aiming for high performance OLED, OFET and organic laser diode, 2008 SID INTERNATIONAL SYMPOSIUM, DIGEST OF TECHNICAL PAPERS, VOL XXXIX, BOOKS I-III, 39, 604-608, 2008.05, We report recent progresses on organic light emitting devices such as organic light emitting diode (OLED), light-emitting organic field effect transistor (LE-OFET) and organic laser diode (OLD). We demonstrate very low driving voltage of OLEDs using a p-i-n structure which also provides high current carrier injection over kA/cm(2). Further we demonstrate novel organic devices such as light emitting FET. We also discuss future prospect of OLD based on our recent materials' development and analysis of operation mechanism.. |
| 144. | Bisri Satria Zulkarnaen, Takenobu Taishi, Yomogida Yohei, Yamao Takeshi, Yahiro Masayuki, Hotta Shu, Adachi Chihaya, Iwasa Yoshihiro, Fabrication of ambipolar light-emitting transistor using high-photoluminescent organic single crystal, ORGANIC OPTOELECTRONICS AND PHOTONICS III, 10.1117/12.781126, 6999, 2008.05. |
| 145. | Robert Gehlhaar, Masayuki Yahiro, Chihaya Adachi, FDTD simulations of external light out-coupling efficiency of organic field-effect transistors, ORGANIC LIGHT EMITTING MATERIALS AND DEVICES XII, 10.1117/12.793569, 7051, 2008.08, We report on three-dimensional numerical optical simulations of the emission extraction efficiency in light emitting devices with field effect carrier transport. The finite difference time domain (FDTD) method is applied for organic thin film structures on silicon substrates with metal and metal oxide electrodes. Simulations are performed for An, Ag and indium tin oxide electrodes in bottom gate, bottom contact geometries. Special attention is paid on the dependence on electrode thickness and contact shape. It is demonstrated that in unipolar driven devices with Si gate, silicon dioxide insulator and 40 inn-thick organic films the maximum out-coupling efficiency is below 10%. This value can be doubled by an implementation of metal reflecting layers on the Si substrate. Furthermore, the emission efficiency in the ambipolar regime is investigated. The results present the dependence of light extraction on the distance between light, source and electrode. Additionally, the influence of the contact edge shape is investigated for two different designs with rectangular and wedge electrodes. Interference effects cause an oscillation in the distance dependence.. |
| 146. | S. Z. Bisri, T. Takahashi, T. Takenobu, M. Yahiro, C. Adachi, Y. Iwasa, Ambipolar Tetraphenylpyrene (TPPy) Single-Crystal Field-Effect Transistor with Symmetric and Asymmetric Electrodes, FRONTIERS IN MATERIALS RESEARCH, 10, 103-+, 2008.01, An ambipolar field-effect transistor (FET) based on a 1,3,6,8- tetraphenylpyrene (TPPy) single-crystal, a high photoluminescent material, has been successfully fabricated using symmetric and asymmetric electrodes. Several kinds of metal electrodes have been employed to investigate the charge injection characteristics in the single-crystal FET. Hole and electron mobilities of 0.34 and 7.7x10(-2) cm(2) V-1 s(-1) were achieved by using Au and Ca electrodes, respectively. The ambipolar characteristic of this device gives a prospect for further development in light-emitting FIST operation.. |
| 147. | Bisri Satria Zulkarnaen, Takenobu Taishi, Tsuda Satoshi, Hotta Shu, Adachi Chihaya, Iwasa Yoshihiro, 22aTB-4 Unique Optoelectronic Properties of Organic Single-Crystal Ambipolar Light-Emitting Transistors, 日本物理学会講演概要集, 10.11316/jpsgaiyo.63.2.4.0_759_1, 63, 0, 759-759, 2008.08. |
| 148. | Hajime Nakanotani, Chihaya Adachi, Organic light-emitting devices using organic thin-film single crystals, EURODISPLAY 2009, 50-51, 2009.09, In this paper, we demonstrate single crystal organic light emitting diodes (OLEDs). The OLEDs were operated with one order of magnitude lower electrical field for the onset of carrier injection and transport compared to conventional OLEDs. Organic single crystals are also useful for significant improvement of light emitting characteristics in ambipolar organic :field effect transistors.. |
| 149. | Masaya Hirade, Hajime Nakanotani, Reiji Hattori, Akihiro Ikeda, Masayuki Yahiro, Chihaya Adachi, Low-Threshold Blue Emission from First-Order Organic DFB Laser Using 2,7-bis[4-(N-carbazole)phenylvinyl]-9,9 '-Spirobifluorene as Active Gain Medium, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 10.1080/15421400902938928, 504, 1-8, 2009.06, s We demonstrate optically excited lasing by an organic semiconducting thin-film based on 2,7-bis[4-(N-carbazole)phenylvinyl]-9,9'-spirobifluorene (spiro-SBCz) as an active gain medium with a first-order distributed feedback (DFB) reflector. We prepared DFB reflectors with periods from 132.5 to 145.00 nm and grooves from 70 to 140 nm depth by using electron-beam-lithography and plasma-etching techniques. The laser having a reflector with a 145.0 nm period had a lasing threshold of 0.72 +/- 0.07 mu J/cm(2), 83% lower than its threshold of amplified spontaneous emission (4.1 +/- 0.4 mu J/cm(2)).. |
| 150. | H. Watanabe, M. Yahiro, Y. Yang, Y. Oki, C. Adachi, Durable & printable blue-violet DFB solid-state dye lasers using spirobifluorene derivatives, 2009 LASERS & ELECTRO-OPTICS & THE PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS, VOLS 1 AND 2, 10.1109/CLEOPR.2009.5292352, 1184-+, 2009.12, Spirobifluorene derivative, as novel and high performance organic compound for light emitting diodes, shows laser action in a distributed feedback waveguide cavity This compound was developed for wet process such as a pritable laser fabrication system Spirobifluorene-doped distributed feedback solid-state laser shows loger durability than traditional. |
| 151. | Takatoshi Nishio, Makoto Kashiwagi, Koji Miyazaki, Masayuki Yahiro, Chihaya Adachi, Preparation under High Humidity Conditions of Nanoporous Polymer Film with 80 nm Minimum Pore Size, APPLIED PHYSICS EXPRESS, 10.1143/APEX.3.025201, 3, 2, 2010.02, Nanoporous polymer film with the smallest pore size of 80 nm was obtained from 0.2 wt% polystyrene/dichloromethane solution at 4 degrees C by the dip-coating method in conjunction with an evaporative humidifier. Fabrication parameters affecting the pore size such as wet coating thickness, solution temperature, and nozzle-substrate gap were varied. The distance between pores depends on the nozzle-substrate gap. For fabrication of the nanosized pores, an appropriate drying time prevents the water droplets from coalescing. Formation of the nanoporous surface structure in the films depends on the solution concentration and solution temperature preventing too rapid drying. (C) 2010 The Japan Society of Applied Physics DOI: 10.1143/APEX.3.025201. |
| 152. | Daisuke Yokoyama, Chihaya Adachi, Horizontal Molecular Orientation in Vacuum-Deposited Organic Amorphous Films, WOLEDS AND ORGANIC PHOTOVOLTAICS: RECENT ADVANCES AND APPLICATIONS, 10.1007/978-3-642-14935-1_5, 137-+, 2010.10, Organic amorphous films fabricated by vacuum deposition have been used as essential components in organic light-emitting diodes (OLEDs) because they have the advantages of nanometer-scale surface smoothness and easy controllability of thickness. However, molecular orientation in organic amorphous films has been disregarded for the past 20 years since the beginning of the research on OLEDs. Here, we demonstrate horizontal molecular orientation in neat and doped organic amorphous films and show the general relationship between molecular structures and the molecular orientation. It was found that when molecular structure is linear or planar, the anisotropy of the molecular orientation in films becomes generally large. The results show the vital importance of the horizontal molecular orientation to understand the light emission and the carrier transport in OLEDs. To elucidate the device physics in OLEDs, the molecular orientation in amorphous films should generally be taken into consideration.. |
| 153. | Manabu Nakata, Kenji Kawano, Mao Yasumatsu, Masayuki Yahiro, Chihaya Adachi, Formation of Organic Nanodots with a Minimum Diameter of 40 nm Using Conventional Vacuum Vapor Deposition, APPLIED PHYSICS EXPRESS, 10.1143/APEX.3.055201, 3, 5, 2010.04, Conventional vacuum deposition onto a substrate coated with a self-assembled monolayer (SAM) was used to produce arrays of hemispherical nanostructures composed of organic semiconducting materials with low molecular weight. The nanostructures had a minimum diameter of 40 nm, indicating that cluster formation occurred in the gas phase during vacuum deposition. The size and shape of the nanostructures were controlled by the underlying SAMs, organic semiconducting materials, film thickness and substrate temperature. (C) 2010 The Japan Society of Applied Physics. |
| 154. | Hirotaka So, Hirofumi Watanabe, Yu Yang, Yuji Oki, Chihaya Adachi, Masayuki Yahiro, A distributed-feedback organic waveguide blue laser using spirobifluorene derivatives, TENCON 2010: 2010 IEEE REGION 10 CONFERENCE, 440-443, 2010.11, In this study, we synthesized the new spirobifluorene derivatives; hexylbiphenyl-spirobifluorene (HBP-Spiro) and demonstrated the operation of a distributed-feedback polymer waveguide blue laser. In addition, we investigated the optical and lasing properties of spirobifluorene derivatives including photostability. The maximum experimental slope efficiency and the energy threshold of a HBP-Spiro-doped waveguide laser were 3.6% and 1.9 mu J, respectively. An operation lifetime of 27,000 shots was obtained for a pump-pulse duration of 1.2 ns and energy of 3.0 mu J at a wavelength of 355 nm.. |
| 155. | Chihaya Adachi, Novel Concept Organic Semiconductors Useful for Organic Light Emitting Diodes, IDW'11: PROCEEDINGS OF THE 18TH INTERNATIONAL DISPLAY WORKSHOPS, VOLS 1-3, 791-794, 2011.12, We report a material having a very small energy gap between its singlet and triplet excited states, Delta E1-3, that realizes efficient up-conversion of triplet excitons into a singlet state, leading to efficient thermally activated delayed fluorescence (TADF). Our molecule, 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-tria zine (PIC-TRZ), broke the large energy gap restriction, providing a quite small Delta E1-3 of 0.11 eV while maintaining a high fluorescent radiative decay rate (k(r)similar to 10(7)). The intense TADF provides a novel pathway for high efficiency electroluminescence.. |
| 156. | Barry P. Rand, Chihaya Adachi, Volker Van Elsbergen, Proceedings of SPIE - The International Society for Optical Engineering: Introduction, Proceedings of SPIE - The International Society for Optical Engineering, 10.1117/12.978944, 8435, 2012.04, This PDF file contains the front matter associated with SPIE Proceedings Volume 8435, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).. |
| 157. | Yu Seok Yang, Takuma Yasuda, Chihaya Adachi, Organic Single-Crystal Transistors Based on π-Extended Heteroheptacene Microribbons, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20120178, 85, 11, 1186-1191, 2012.11, Facile synthesis of a new series of pi-extended thienoacenes has been described. Their electronic structures have been elucidated by UV-vis absorption and photoelectron spectra. Well-defined single-crystal microribbons composed of self-organized thienoacene molecules have been fabricated using physical vapor transport, and have been applied to field-effect transistors. The organic transistors employing the single-crystal microribbons exhibit mobilities as high as 0.47 cm(2) V s(-1) with on/off ratios of ca. 10(6).. |
| 158. | T. Kasahara, J. Mizuno, S. Hirata, T. Edura, S. Matsunami, C. Adachi, S. Shoji, MICROFLUIDIC ORGANIC LIGHT EMITTING DIODE (OLED) USING LIQUID ORGANIC SEMICONDUCTORS, 2012 IEEE 25TH INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS), 10.1109/MEMSYS.2012.6170256, 2012.01, We propose a first prototype of the microfluidic organic light emitting diode (OLED). A matrix of 3x3 OLED array was fabricated in the SU-8 microchannels sandwiched by the indium tin oxide (ITO) anode and cathode. The liquid organic semiconductors were employed for the light emitters and were injected into the microchannels. The electroluminescence was obtained in the microchannels under the optimized applied voltage. The current density of 2.11 mA/cm(2) was measured at 60 V. Since flesh liquid organic semiconductors are continuously supplied to the emitting layer, long-term stable electroluminescence is expected by the proposed OLED.. |
| 159. | Kenichi Goushi, Chihaya Adachi, Delayed Fluorescence by Reverse Intersystem Crossing and Application to Organic Light-Emitting Diodes, 2012 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO), 2012.05, Organic donor and acceptor interfaces give rise to a small energy gap between the singlet and triplet exciton levels (Delta E-ST) of generated exciplexes. We demonstrate that the small. Delta E-ST can lead to efficient electroluminescence.. |
| 160. | T. Kasahara, J. Mizuno, S. Matsunami, T. Edura, M. Tsuwaki, J. Oshima, C. Adachi, S. Shoji, Variable multi-color microfluidic organic light emitting device based on mixing of electrochemiluminescence solutions, 2013 Transducers and Eurosensors XXVII: The 17th International Conference on Solid-State Sensors, Actuators and Microsystems, TRANSDUCERS and EUROSENSORS 2013, 10.1109/Transducers.2013.6627337, 2596-2599, 2013.01, We developed a variable multi-color microfluidic organic light emitting device based on mixing of different electrochemiluminescence (ECL) solutions. The prototype of microfluidic device consisted of Y-shaped SU-8 microchannels sandwiched between polyethylene naphthalate (PEN) and glass substrates having indium tin oxide (ITO) anode and cathode pairs. 5,6,11,12-tetraphenylnaphthacene (rubrene) and tetraphenyldibenzoperiflanthene (DBP) doped rubrene were used as ECL materials. Yellow, red, and orange color emissions from the ECL cell were obtained by changing DBP concentration in rubrene solution. Multi-color ECL was confirmed from the fabricated Y-shaped microfluidic device before and after mixing of ECL solutions. © 2013 IEEE.. |
| 161. | T. Kasahara, J. Mizuno, S. Matsunami, T. Edura, M. Tsuwaki, J. Oshima, C. Adachi, S. Shoji, MULTI-COLOR MICROFLUIDIC ORGANIC LIGHT EMITTING DEVICE USING ELECTROLUMINESCENCE AND ELECTROCHEMILUMINESCENCE, 26TH IEEE INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS 2013), 10.1109/MEMSYS.2013.6474450, 1133-1136, 2013.01, We developed a multi-color microfluidic organic light emitting device, which consists of liquid organic light emitting diodes (OLEDs) and electrochemiluminescence (ECL) devices. A 3 x 3 matrix of emitting pixels was fabricated in SU-8 microchannels sandwiched between polyethylene naphthalate (PEN) and glass substrates with indium tin oxide (ITO) anode and cathode pairs. Liquid organic semiconductor and ECL solutions as liquid emitters were injected into the microchannels. The electroluminescence (EL) and ECL were successfully obtained at the emitting pixels in the microchannels. The proposed structure can be applicable for multi-color liquid-based display.. |
| 162. | Tomas Serevicius, Tetsuya Nakagawa, Ming-Cheng Kuo, Shuo-Hsien Cheng, Ken-Tsung Wong, Chih-Hao Chang, Raymond C. Kwong, Sean Xia, Chihaya Adachi, Enhanced electroluminescence based on thermally activated delayed fluorescence from a carbazole-triazine derivative, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 10.1039/c3cp52255e, 15, 38, 15850-15855, 2013.10, Thermally activated delayed fluorescence (TADF) properties of a dicarbazole-triazine compound, 9-(4,6diphenyl-1,3,5-triazin-2-yl)-9'-phenyl-3,3'-bicarbazole (CzT), and its OLED characteristics were investigated. An estimated small energy gap of about 90 meV between the singlet and triplet energy states of CzT made the up-conversion of triplet excitons back to a singlet state possible. The origin of the observed delayed fluorescence has been shown to be thermally activated delayed fluorescence. An organic light emitting diode (OLED) with CzT as an emitter showed the maximum external quantum efficiency (EQE) of 6%. For comparison, another carbazole-triazine derivative of 3-(2'-( 4,6-diphenyl-1,3,5-triazin-2-yl)[1,1'-biphenyl]-2-yl)-9-phenyl-9H-carbazole (PhCzTAZ) with a similar structure was also studied. PhCzTAZ showed a low fluorescence quantum yield with no TADF.. |
| 163. | Keiro Nasu, Tetsuya Nakagawa, Hiroko Nomura, Chi-Jen Lin, Chien-Hong Cheng, Mei-Rurng Tseng, Takuma Yasuda, Chihaya Adachi, A highly luminescent spiro-anthracenone-based organic light-emitting diode exhibiting thermally activated delayed fluorescence, CHEMICAL COMMUNICATIONS, 10.1039/c3cc44179b, 49, 88, 10385-10387, 2013.11, Efficient thermally activated delayed fluorescence was observed from a spiro-anthracenone derivative (ACRSA). An organic light-emitting diode containing ACRSA exhibited blue-greenish electroluminescence with a maximum external quantum efficiency of 16.5%.. |
| 164. | Yoshiharu Ajiki, Tetsuo Kan, Masayuki Yahiro, Akiko Hamada, Junji Adachi, Chihaya Adachi, Kiyoshi Matsumoto, Isao Shimoyama, NEAR INFRARED PHOTO-DETECTOR USING SELF-ASSEMBLED FORMATION OF ORGANIC CRYSTALLINE NANOPILLAR ARRAYS, 2014 IEEE 27TH INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS), 147-150, 2014.01, We proposed a near infrared photo-detector (NIR-PD) using self-assembled formation of organic crystalline arrays, which were formed on an n-type silicon (n-Si) substrate and covered with an Au film. These structures act as antennas for near infrared (NIR) light, resulting in an enhancement of the light absorption on the Au film. The NIR-PDs thus have higher photo-responsivity compared with that of an Au/n-Si typed Schottky diodes, which was fabricated as a reference. In this paper, the fabrication process of the NIR-PDs and the estimation results of photo-responsivity were described. The maximum responsivity to NIR light (wavelength = 1.2 mu m) was 1.79 mA/W without applying forward bias. This value is 10 times larger than the responsivity of the Au/n-Si typed Schottky diode as a reference.. |
| 165. | Miho Tsuwaki, Jun Mizuno, Takashi Kasahara, Tomohiko Edura, Eri Kunisawa, Ryoichi Ishimatsu, Shigeyuki Matsunami, Toshihiko Imato, Chihaya Adachi, Shuichi Shoji, MICROFLUIDIC ELECTROCHEMILUMINESCENCE (ECL) INTEGRATED FLOW CELL FOR PORTABLE FLUORESCENCE DETECTION, 2014 IEEE 27TH INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS), 108-111, 2014.01, We propose a portable electrochemiluminescence (ECL)-induced fluorescence chip which consists of flow channels for fluorescence sample and multi-color emitting ECL excitation source. A prototype ECL-induced fluorescence chip was fabricated by conventional photolithography and bonding technique. Device performance was evaluated using ECL of rubrene as excitation source and resorufin as fluorescent dye. Fluorescence of 500 mu M resorufin (600 nm) was successfully detected using 10 mM rubrene solution (560 nm) under the applied voltage of 4 V. The proposed principle is applicable for portable and on-demand multi fluorescence detection device using its freedom of choice for combination of the ECL light source.. |
| 166. | Fengshou Wu, Jie Li, Hongbo Tong, Zaoying Li, Chihaya Adachi, Adam Langlois, Pierre D. Harvey, Li Liu, Wai-Yeung Wong, Wai-Kwok Wong, Xunjin Zhu, Phosphorescent Cu(I) complexes based on bis(pyrazol-1-yl-methyl)-pyridine derivatives for organic light-emitting diodes, JOURNAL OF MATERIALS CHEMISTRY C, 10.1039/c4tc01885k, 3, 1, 138-146, 2015.01, Mononuclear Cu(I) complexes based on bis(pyrazol-1-yl-methyl)-pyridine derivatives and ancillary triphenylphosphine have been prepared and characterized by H-1 NMR, mass spectroscopy and single-crystal X-ray analysis. The thermogravimetric analysis shows that the complexes exhibit high thermal stability. The electronic absorption spectra display two features in the regions of 230-260 and 290-350 nm attributable to mixed ligand-to-ligand (LLCT) and metal-to-ligand-charge-transfer (MLCT) excited states, which is supported by the results of density functional theory (DFT) and time-dependent DFT (TDDFT) calculations on these Cu(I) complexes. These complexes are strongly emissive in the solid state at ambient temperature. Intense blue or green emission in the poly(methyl methacrylate) film is observed in the region of 475-518 nm for these complexes with the emission lifetimes in the microsecond time scale (12-20 mu s), indicating that the emission may be phosphorescence emission. Increasing the steric hindrance of the substituents on the pyrazole unit results in a blue-shift of the emission bands and enhanced emission quantum efficiency in PMMA films. The two most emissive complexes have been used for the fabrication of phosphorescent organic light-emitting diodes (POLEDs).. |
| 167. | Hironori Kaji, Katsuyuki Shizu, Furitsu Suzuki, Tatsuya Fukushima, Katsuaki Suzuki, Chihaya Adachi, Organic Light-Emitting Diodes: Multiscale Charge Transport Simulation and Fabrication of New Thermally Activated Delayed Fluorescence (TADF) Materials, ORGANIC LIGHT EMITTING MATERIALS AND DEVICES XIX, 10.1117/12.2189078, 9566, 2015.09, Charge transports in amorphous thin films with 100 nm thickness are investigated in silico by explicitly considering organic molecules. The amorphous layer of organic molecules was constructed using molecular dynamics simulations. The rate constants for charge hopping between two organic molecules, extracted from the amorphous layers, were calculated based on quantum chemical calculations. The hopping transport in amorphous layers was simulated using a Monte Carlo method. The hole mobility was calculated to be several times larger than the electron mobility, which was consistent with the experimental results. The Monte Carlo simulation also shows that diffusion transport is dominant at low applied electric fields and that contribution of drift transport increases at high electric fields. The simulation in this study enables us to reveal molecular origin of charge transport. In the presentation, we will show the results on recently-developed new thermally activated delayed fluorescence materials and the device performances.. |
| 168. | Chuanjiang Qin, Toshinori Matsushima, Chihaya Adachi, Degradation mechanism of planar perovskite solar cells, ORGANIC PHOTOVOLTAICS XVI, 10.1117/12.2187578, 9567, 2015.10. |
| 169. | Hosokai Takuya, Matsuzaki Hiroyuki, Furube Akihiro, Tokumaru Katsumi, Tsutsui Tetsuo, Nakanotani Hajime, Yahiro Masayuki, Adachi Chihaya, Role of intermediate state in the excited state dynamics of highly efficient TADF molecules, ORGANIC LIGHT EMITTING MATERIALS AND DEVICES XX, 10.1117/12.2236248, 9941, 2016.09. |
| 170. | Atula S. D. Sanadanayaka, Kou Yoshida, Jean-Charles Ribierre, Toshinori Matsushima, Chihaya Adachi, Quasi continuous-wave lasing in organic thin-film semiconductors, ORGANIC LIGHT EMITTING MATERIALS AND DEVICES XX, 10.1117/12.2237466, 9941, 2016.11. |
| 171. | 山田, 洋一, 長谷川, 友里, 細貝, 拓也, 中野谷, 一, 安達, 千波矢, Enrique, Ortega, 熱活性型遅延蛍光（TADF)分子の配向制御と電子状態評価, 表面科学学術講演会要旨集, 10.14886/sssj2008.37.0_3, 37, 0, 3-3, 2017.08, 熱活性型遅延蛍光(TADF)は、三重項励起子を熱励起により一重項励起子に逆項間交差させることで、内部量子効率100%の蛍光発光を可能にする。この分子を用いたデバイスの外部量子効率を向上させるため、配向制御により遷移双極子モーメントを揃えることで、光取出効率を向上させることが重要である。我々は、この分子の配向制御を達成し、さらに配向膜の電子状態が孤立分子と同様であることを示した。. |
| 172. | 南, 颯人, 佐々木, 正洋, 山田, 洋一, 細貝, 拓也, 中野谷, 一, 安達, 千波矢, 長谷川, 友里, TADF分子膜の配向制御及び発光特性計測, 表面科学学術講演会要旨集, 10.14886/sssj2008.37.0_212, 37, 0, 212-212, 2017.08, 熱活性遅延蛍光分子は、緻密な分子設計によって内部量子効率100%を実現することが知られている。高効率の有機ELデバイス実現のためには、高い内部量子効率の維持が重要であると考える。我々は金属基板上でいくつかのTADF分子について高配向の単分子膜を形成し、STMにより構造解析を行った。また、過渡発光計測の結果、TADF分子の一種である4CzIPNは遅延蛍光の発光効率が膜厚に依存することを見出した。. |
| 173. | Hiroshi Fujimoto, Takashi Suekane, Katsuya Imanishi, Satoshi Yukiwaki, Hong Wei, Kaori Nagayoshi, Masayuki Yahiro, Chihaya Adachi, Influence of vacuum chamber impurities on OLED degradation, Digest of Technical Papers - SID International Symposium, 10.1002/sdtp.11560, 48, 1, 9-12, 2017.12, We evaluated the influence of impurities in the vacuum chamber used for device fabrication on the lifetime ofOLEDs and found a correlation between lifetime and the device fabrication time. Our results suggest that impurities including previously deposited materials and plasticizers from the chamber components impact lifetime and reproducibility.. |
| 174. | Naofumi Kobayashi, Hiroyuki Kuwae, Juro Oshima, Ryoichi Ishimatsu, Shuya Tashiro, Toshihiko Imato, Chihaya Adachi, Shuichi Shoji, Jun Mizuno, Deep-blue light emission with a wide-bandgap naphthalene-derivative liquid organic semiconductor host, ORGANIC PHOTONIC MATERIALS AND DEVICES XIX, 10.1117/12.2251640, 10101, 2017.02, We developed a novel naphthalene-derivative to function as a wide-bandgap liquid organic semiconductor (LOS) host material for the limited range of liquid deep-blue light-emitting materials that have been developed to date. The naphthalene-derivative, 1-naphthaleneacetic acid 2-ethylhexyl ester (NLQ) was synthesized as a LOS, by introducing an ethylhexyl group into naphthalene. 9,10-Diphenyl anthracene (DPA) was doped into NLQ as a guest deep-blue dye. From the absorption spectrum, the bandgap energy of NLQ was estimated to be 4.13 eV, indicating that NLQ has the widest bandgap energy of any such host material so far as we know. Deep-blue electroluminescence (EL) emission in a liquid state was obtained by doping DPA into NLQ. Light emission could be achieved by a combination of Forster resonance energy transfer and direct recombination of trapped holes and electrons because the bandgap energy of DPA is straddle by that of the wide-bandgap NLQ. Thus, NLQ is shown to be a promising wide-bandgap LOS host material, which allows deep-blue light emission and may have applications in liquid organic light-emitting diodes.. |
| 175. | H. Mieno, R. Kabe, M. D. Allendorf, C. Adachi, Thermally activated delayed fluorescence of a Zr-based metal–organic framework, Chemical Communications, 10.1039/c7cc08595h, 54, 6, 631-634, 2018.01, The first metal–organic framework exhibiting thermally activated delayed fluorescence (TADF) was developed. . |
| 176. | Michel Frigoli, Tanguy Jousselin-Oba, Masashi Mamada, Jérôme Marrot, Agnese Zangarelli, Danilo Pannacci, Chihaya Adachi, Fausto Ortica, Synthesis and photochromic behaviour of a series of benzopyrans bearing an N-phenyl-carbazole moiety: photochromism control by the steric effect, Photochemical & Photobiological Sciences, 10.1039/d0pp00202j, 19, 10, 1344-1355, 2020.10, The phenyl group in blue controls the photochromism of [3 |
| 177. | Tanguy Jousselin-Oba, Masashi Mamada, Atsushi Okazawa, Jérome Marrot, Takayuki Ishida, Chihaya Adachi, Abderrahim Yassar, Michel Frigoli, Modulating the ground state, stability and charge transport in OFETs of biradicaloid hexahydro-diindenopyrene derivatives and a proposed method to estimate the biradical character, Chemical Science, 10.1039/d0sc04583g, 11, 44, 12194-12205, 2020.11, Biradicaloid HDIP derivatives show that the Δ |
| 178. | Yizhong Shi, Kai Wang, Youichi Tsuchiya, Wei Liu, Takeshi Komino, Xiaochun Fan, Dianming Sun, Gaole Dai, Jiaxiong Chen, Ming Zhang, Caijun Zheng, Shiyun Xiong, Xuemei Ou, Jia Yu, Jiansheng Jie, Chun-Sing Lee, Chihaya Adachi, Xiaohong Zhang, Hydrogen bond-modulated molecular packing and its applications in high-performance non-doped organic electroluminescence, Materials Horizons, 10.1039/d0mh00952k, 7, 10, 2734-2740, 2020.10, Suitable intermolecular hydrogen bonding enables the formation of a fixed 3D supramolecular framework and suppresses the exciton nonradiative decays and quenching. . |
| 179. | Masashi Mamada, Ryota Nakamura, Chihaya Adachi, Synthesis, crystal structure and charge transport characteristics of stable peri-tetracene analogues, Chemical Science, 10.1039/d0sc04699j, 12, 2, 552-558, 2021.01, Highly stable |
| 180. | Džiugas Litvinas, Ramūnas Aleksiejūnas, Patrik Ščajev, Paulius Baronas, Vaiva Soriūtė, Chuanjiang Qin, Takashi Fujihara, Toshinori Matsushima, Chihaya Adachi, Saulius Juršėnas, Energy transfer in (PEA)2FAn−1PbnBr3n+1 quasi-2D perovskites, Journal of Materials Chemistry C, 10.1039/d1tc00422k, 9, 14, 4782-4791, 2021.03, Simultaneous fast energy funnelling between the neighbouring sheets and slower carrier and exciton in-plane diffusion revealed in quasi-2D perovskites. . |
| 181. | Yuya Oyama, Masashi Mamada, Akihiro Kondo, Chihaya Adachi, Advantages of naphthalene as a building block for organic solid state laser dyes: smaller energy gaps and enhanced stability, Journal of Materials Chemistry C, 10.1039/d0tc05387b, 9, 12, 4112-4118, 2021.02, The introduction of naphthalene units into a stilbene structure improves not only the PL quantum yield but also stability. The emission wavelength is redshifted upon π-extension, resulting in the realization of excellent green laser dyes. . |
| 182. | C ADACHI, S TOKITO, T TSUTSUI, S SAITO, ORGANIC ELECTROLUMINESCENT DEVICE WITH A 3-LAYER STRUCTURE, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 10.1143/JJAP.27.L713, 27, 4, L713-L715, 1988.04. |
| 183. | C ADACHI, S TOKITO, T TSUTSUI, S SAITO, ELECTROLUMINESCENCE IN ORGANIC FILMS WITH 3-LAYER STRUCTURE, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 10.1143/JJAP.27.L269, 27, 2, L269-L271, 1988.02. |
| 184. | T MORIKAWA, C ADACHI, T TSUTSUI, S SAITO, MULTILAYER-TYPE ORGANIC SOLAR-CELLS USING PHTHALOCYANINES AND PERYLENE DERIVATIVES, NIPPON KAGAKU KAISHI, 10.1246/nikkashi.1990.962, 9, 962-967, 1990.09. |
| 185. | Y HAMADA, C ADACHI, T TSUTSUI, S SAITO, OXADIAZOLE DERIVATIVES FOR EMITTER AND CARRIER TRANSPORT MATERIALS IN ORGANIC ELECTROLUMINESCENT DEVICES, NIPPON KAGAKU KAISHI, 10.1246/nikkashi.1991.1540, 11, 1540-1548, 1991.11, Ten oxadiazole derivatives which were newly synthesized were examined as an emitter in organic electroluminescence (EL) cells. The new oxadiazole derivatives exhibited the photoluminescence (PL) peaks at the wavelength region between 374 and 527 nm. Vacuum-deposited thin films of these compounds had excellent thermal stability, because they have high melting temperature ranging from 240 to 365-degrees-C. The organic EL cells with 4,4'-bis[5-(p-dimethylaminophenyl)-1,3,4-oxadiazol-2-yl]biphenyl, 1,3-bis[5-(p-dimethylaminophenyl)-1,3,4-oxadiazol-2-yl]benzene and 1,4-bis[5-(p-dimethylaminophenyl)-1,3,4-oxadiazol-2-yl]benzene as an emitter showed bright emission whose intensities were 1000 approximately 2000 cd/m2. The emission colors were green, blue, and green, respectively. These three oxadiazole derivatives were found to exhibit specific electronic characteristics that they transport both holes and electrons. Utilization of these materials for both emitter and electron transport materials were demonstrated.. |
| 186. | T TSUTSUI, C ADACHI, S SAITO, ELECTROLUMINESCENCE IN MULTILAYER ORGANIC-DYE FILMS, SYNTHETIC METALS, 10.1016/0379-6779(91)91588-2, 41, 3, 1193-1196, 1991.05, High efficiency electroluminescent devices using organic multilayer dye films were fabricated. Mechanism of electroluminescence in the multilayer dye films is described. The importance of the confinements of both charge carriers and molecular excitons within narrow emission regions was emphasized.. |
| 187. | T TSUTSUI, C ADACHI, S SAITO, M WATANABE, M KOISHI, EFFECT OF CONFINED RADIATION-FIELD ON SPONTANEOUS-EMISSION LIFETIME IN VACUUM-DEPOSITED FLUORESCENT DYE FILMS, CHEMICAL PHYSICS LETTERS, 10.1016/0009-2614(91)80118-H, 182, 2, 143-146, 1991.07, Spontaneous emission lifetimes of fluorescent dye layers in front of a metallic mirror were observed using a picosecond time-resolved fluorescence measurement system. Multilayer thin-film samples composed of glass substrate/indium-tinoxide layer/organic spacer layer/emission dye layer/organic spacer layer/MgAg mirror were prepared with vacuum-vapor deposition. The distance between an MgAg mirror and an emission dye layer was varied from 25 to 180 nm. The emission lifetime of the fluorescent dye layer largely depended on the MgAg mirror-emission layer distance and assumed a maximum at around 150 nm. A promising application of organic multilayer structures for the study on optical microcavity was suggested.. |
| 188. | M ERA, C ADACHI, T TSUTSUI, S SAITO, DOUBLE-HETEROSTRUCTURE ELECTROLUMINESCENT DEVICE WITH CYANINE-DYE BIMOLECULAR LAYER AS AN EMITTER, CHEMICAL PHYSICS LETTERS, 10.1016/0009-2614(91)87007-X, 178, 5-6, 488-490, 1991.04, Using the Langmuir-Blodgett technique, we fabricated a double-heterostructure electroluminescent (EL) device with a J-aggregated cyanine-dye bimolecular layer as an emitting layer. The EL cells were composed of an indium tin oxide electrode, a diamine hole-transport layer, a J-aggregated cyanine-dye emitting layer, an oxadiazole electron-transport layer and an MgAg electrode. Efficient EL was observed in the EL device owing to the confinement of charge carriers and excitons within the cyanine-dye bimolecular layer. The EL spectrum corresponded well to resonance fluorescence of the J-aggregate.. |
| 189. | Y FUJITA, C ADACHI, T TSUTSUI, S SAITO, RELATION BETWEEN MOLECULAR-STRUCTURES OF DYES AND PHOTOVOLTAIC PROPERTIES IN 2 LAYER ORGANIC SOLAR-CELLS USING PHTHALOCYANINES AND PERYLENETETRACARBOXYLIC ACID-DERIVATIVES, NIPPON KAGAKU KAISHI, 10, 1154-1161, 1992.10, Photovoltaic Properties of two-layer organic solar cells were investigated. Metal phthalocyanines (MPc) and porphyrins (Por) shown in Fig.1 were employed for p-type layer. 3, 4 : 9. 10-Bis(imidazo[1, 2-a]pyrido-fused)perylene derivatives (PTCIz) shown in Fig. 2 were employed for n-type layer. The cell structure was indium-tin oxide(ITO)/n-type layer/p-type layer/Au and the cells were irradiated with white light through the ITO electrode. The thicknesses of organic layers were 500 angstrom. Positive voltage appeared on an Au electrode under illumination in all the cells. Short-circuit current was proportional to the incident light intensity (Fig. 9), and open-circuit voltage was proportional to the log (incident light intensity) (Fig. 10). The photocurrent spectra reflected the absorption spectra of MPc or Por layers, indicating the occurrence of effective carrier generation in MPc or Por layers. The short-circuit current of the cells ranged between 0. 89 and 0. 004 mA/cm2 at the incident light power of 15 mW/cm2 (Tables 1, 2 and 3). The open-circuit voltage ranged between 0. 74 and 0. 15 V. The fill factor ranged between 0. 63 and 0. 21. Short-circuit current was most profoundly influenced, when chemical structures of dyes were varied. The energy conversion efficiencies of the cells using MPc and PTCIz ranged between 1. 9 and 0. 002%.. |
| 190. | M ERA, C ADACHI, T TSUTSUI, S SAITO, ORGANIC ELECTROLUMINESCENT DEVICE WITH CYANINE DYE LANGMUIR-BLODGETT-FILM AS AN EMITTER, THIN SOLID FILMS, 10.1016/0040-6090(92)90314-2, 210, 1-2, 468-470, 1992.04, Double hetero-structure electroluminescent (EL) devices with a cyanine dye LB film as an emitter were prepared. The cyanine dye formed J-aggregate in the LB film, and intense fluorescence with very narrow bandwidth was observed in the LB film. When DC voltage was applied to the devices, EL corresponded well with the resonance fluorescence of the J-aggregated cyanine dye. As a result of confinement of charge carriers and excitons within the cyanine dye emitter, efficient electroluminescence was attained even in the device with the J-aggregated cyanine dye bimolecular layer as an emitter.. |
| 191. | Y HAMADA, C ADACHI, T TSUTSUI, S SAITO, BLUE-LIGHT-EMITTING ORGANIC ELECTROLUMINESCENT DEVICES WITH OXADIAZOLE DIMER DYES AS AN EMITTER, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 10.1143/JJAP.31.1812, 31, 6A, 1812-1816, 1992.06, Multilayer thin-film electroluminescent devices with blue emission color have been fabricated using new oxadiazole dimer dyes for both emission and electron transport layers. Emission characteristics of three types of cells, SH-A: ITO/HTL/EML/MgAg, SH-B: ITO/EML/ETL/MgAg and DH: ITO/HTL/EML/ETL/MgAg, in which ITO, HTL, EML, ETL and MgAg represent indium-tin-oxide cathode, hole transport layer, emission layer, electron transport layer and magnesium-silver alloy anode, respectively, are compared. Luminances exceeding 1000 cd/m2 are observed and emission peaks are located at 470-480 nm. Among the three cells, the DH cell shows the best performance. The DH cell is stable for more than 40-day storage and can also be continuously driven for more than one hour at room temperature and 7 h at liquid nitrogen temperature.. |
| 192. | C ADACHI, K NAGAI, N TAMOTO, MOLECULAR DESIGN OF HOLE TRANSPORT MATERIALS FOR OBTAINING HIGH DURABILITY IN ORGANIC ELECTROLUMINESCENT DIODES, APPLIED PHYSICS LETTERS, 10.1063/1.113123, 66, 20, 2679-2681, 1995.05. |
| 193. | C Adachi, K Nagai, N Tamoto, Durability characteristics of aminopyrene dimer molecules as an emitter in organic multilayered electroluminescent diodes, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 10.1143/JJAP.35.4819, 35, 9A, 4819-4825, 1996.09, We report the structure design of emitter molecules using aminopyrene dimers for obtaining durable organic electroluminescent (EL) diodes. Using eighteen kinds of emitter molecules having a variety of substituents and linking groups, we investigated the durability of the cell structure of the anode/hole transport layer/emitter layer/electron transport layer 2/electron transport layer 1/cathode. We observed that the chemical structures of the emitter molecules strongly influenced the durability of the EL devices under continuous DC operation. Mie observed no direct relationships between melting point (T-m); glass transition temperature (T-g), ionization potential (I-p), electron affinity (E(a)) of emitter layers and EL device durabilities. The effect of the substituent groups of emitter molecules on EL device durability suggests that the chemical stability of the emitter molecules largely influences EL device durability.. |
| 194. | C Adachi, S Hibino, T Koyama, Y Taniguchi, Submicrometer-sized organic light emitting diodes with a triphenylamine-containing polycarbonate as a guest molecule in a polymer blend, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 10.1143/jjap.36.L827, 10.1143/JJAP.36.L827, 36, 6B, L827-L830, 1997.06, We fabricated submicrometer-sized organic light emitting diodes (OLED) with bright emission using a polymer blend. The cell structure was composed of ITO (indium-tin oxide)/hole transport layer (polymer blend layer)/emitter layer/MgAg. We used poly (methyl methacrylate) (PMMA) as an inert host material and N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine-polycarbonate (PC-TPD) as a guest material. The PC-TPD formed submicrometer-sized spherical domains, actually prolate spheroids, in the PMMA host layer. With 2 wt% of PC-TPD, the domain diameters were around 200 nm according to atomic force microscopy (AFM) observation. The OLED including such a blend structure appeared as an array of bright submicrometer-sized electroluminescence spots. The number of working diodes exceeded four million per square centimeter.. |
| 195. | N Tamoto, C Adachi, K Nagai, Electroluminescence of 1,3,4-oxadiazole and triphenylamine-containing molecules as an emitter in organic multilayer light emitting diodes, CHEMISTRY OF MATERIALS, 10.1021/cm960391+, 9, 5, 1077-1085, 1997.05, We synthesized five new emitter molecules having an oxadiazole group as an electron transport unit and a triphenylamine group as a hale transport unit. We investigated the electroluminescent (EL) properties of these molecules as an emitter layer. The deposited films of all compounds were found to be amorphous and showed strong blue-green fluorescence, ranging from 450 to 490 nm. With the best device using these emitters, the maximum luminance exceeded 19 000 cd/m(2). We observed that external EL quantum efficiencies (phi(EL)) were drastically influenced by combinations of hole-transport materials. Formation of exciplexes between the emitters and hole-transport materials was found to greatly influence phi(EL) We observed that the hole-transport layers (HTLs) having a low ionization potential (Ip) value tended to form exciplexes with the emitter layers, resulting in a low phi(EL) On the other hand, the HTLs having a large Ip formed no exciplexes with emitter layers and showed a high phi(EL) In the best device, a phi(EL)similar to 4% was obtained. Furthermore, we also studied the optimum EL cell structures using the bipolar emitters. We observed that a double hetero (DH) structure was the best device structure and could achieve an external energy conversion efficiency (phi(energy)) of 3.75 lm/W at a current density of 10 mA/cm(2). This is an excellent value among the organic EL devices previously reported. In addition, the durabilities of the EL devices were also measured at constant current density. Performances of the EL device durabilities were quite inferior with these emitter materials. The time for the luminance to decay to half of the initial luminance was below 1 h.. |
| 196. | S Tanaka, C Adachi, T Koyama, Y Taniguchi, Organic light emitting diodes using triphenylene derivatives as a hole transport material, CHEMISTRY LETTERS, 10.1246/cl.1998.975, 10, 975-976, 1998.10, We elucidated that hexaalkoxytriphenylenes (HATs) are useful as a hole transport layer (HTL) in organic light emitting diodes (OLEDs). In particular, the insertion of a thin phthalocyanine layer between the anode and HTL drastically improved electroluminescent (EL) performance. Furthermore, we observed that the alkyl chain length of HATs greatly affected carrier transport and EL properties.. |
| 197. | G Sakamoto, C Adachi, T Koyama, Y Taniguchi, CD Merritt, H Murata, ZH Kafafi, Significant improvement of device durability in organic light-emitting diodes by doping both hole transport and emitter layers with rubrene molecules, APPLIED PHYSICS LETTERS, 10.1063/1.124506, 75, 6, 766-768, 1999.08, We have developed highly durable organic light-emitting diodes. The basic structure of the diodes is anode/hole injection layer/hole transport layer+dopant/emitter layer+dopant/cathode. Both the hole transport and the emitter layers were doped with the highly fluorescent rubrene molecules. With the doping of both layers, 85% of the initial luminance was successively maintained even after 1000 h of continuous operation under constant current driving. Doping of only one of these layers, either the hole transport layer or emitter layer, on the other hand, resulted in shorter lifetime. We mention the possible mechanisms of the doping that enhance the device duration. (C) 1999 American Institute of Physics. [S0003-6951(99)03132-0].. |
| 198. | A Yamamori, C Adachi, T Koyama, Y Taniguchi, Electroluminescence of organic light emitting diodes with a thick hole transport layer composed of a triphenylamine based polymer doped with an antimonium compound, JOURNAL OF APPLIED PHYSICS, 10.1063/1.371372, 86, 8, 4369-4376, 1999.10, We investigated the electroluminescence (EL) performance of organic light emitting diodes having a thick doped hole transport layer [(DHTL):650 nm-1.5 mu m]. The basic cell structure is an anode/DHTL/hole transport layer [(HTL):50-60 nm]/emitter layer [(EML):50-60 nm]/cathode. We examined various combinations of host polymers and guest molecules as a component of DHTL in this device structure. During the course of the materials' search, we found that the best combination of a hole transport polycarbonate polymer (PC-TPD-DEG) and a tris (4-bromophenyl) aminium hexachroloantimonate (TBAHA) as a dopant enabled us to form a uniform thick DHTL (typically 650 nm-1.5 mu m thick), which resulted in excellent EL performance. The thick DHTL not only showed considerable reduction in cell resistance compared with a conventional anode/DHTL (without doping)/HTL/EML/cathode device with the same thicknesses of the organic layers, but also greatly contributed to the enhancement of the device stability, particularly to pinhole problems that can occur with conventional 100-nm-thick thin devices. Furthermore, the interposed HTL between DHTL and EML was confirmed to function not only as a HTL but also as electron and exciton blocking layers. Without the HTL, the EL quantum efficiency (Phi(EL)) was low, because of the serious exciton energy transfer and/or electron migration from EML to DHTL where the PC-TPD-DEG:TBAHA complex layer had absorption at around 485 nm based on a charge transfer complex between them. We could increase it by interposing a thin transparent N,N'-diphenyl-N,N'-bis(3-methyl phenyl)-1,1'-biphenyl-4,4'-diamine or 4,4'-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl (alpha-NPD) layer between DHTL and EML, while keeping the driving voltage low. With the DHTL (650 nm, 10 wt % of TBAHA) showed a luminance of 4004 cd/m(2) at 10.0 V and 220 mA/cm(2), of which the performance was comparable with that of typical thin film devices. Furthermore, we could expand the DHTL thickness up to 1.5 mu m. An indium tin oxide (ITO)/DHTL (10 wt %)(1.5 mu m)/alpha-NPD (60 nm)/Alq (60 nm)/MgAg device showed a luminance of 2600 cd/m(2) at 18.0 V and 210 mA/cm(2) with enhanced duration stability. In addition, the duration properties of the devices were also examined in the device structure of an ITO/DHTL (650 nm)/alpha-NPD (60 nm)/Alq(doped with rubrene 4.2 wt %) (60 nm)/MgAg. The half decay of the initial luminance successively exceeded over 1000 h under a constant current density of 10 mA/cm(2). (C) 1999 American Institute of Physics. [S0021-8979(99)06020-X].. |
| 199. | N Suganuma, C Adachi, T Koyama, Y Taniguchi, H Shiraishi, A 200nm x 2mm array of organic light-emitting diodes and their anisotropic electroluminescence, APPLIED PHYSICS LETTERS, 10.1063/1.123500, 74, 9, 1206-1208, 1999.03, We demonstrated the fabrication of a 200 nmX2 mm array of organic light-emitting diodes (OLEDs) on a glass substrate. The photolithographic technique using an optical phase shift mask allowed us to construct a super-fine resolution patterning of OLEDs. A single organic electroluminescent (EL) layer composed of an inert poly(methylmethacrylate) polymer binder and tetraphenylbendidine and tris(8-quinolinol) aluminum molecules was fabricated on a fine-resolution photoresist patterning by a spin coating method. The lines and spaces of the photoresist patterning were 200 nm. The emitting area was well confined by the regular array of residual photoresist resin walls. Finally, a MgAg cathode layer was uniformly deposited on the organic layer. We observed anisotropic EL spectra between the directions perpendicular and parallel to the patterning of OLED arrays. Furthermore, we observed a large difference of EL intensities between them. We assume that the anisotropic EL characteristics are caused by the confinement effect of photons inside the submicrometer-sized OLED array. (C) 1999 American Institute of Physics. [S0003-6951(99)02709-6].. |
| 200. | MA Baldo, C Adachi, Forrest, SR, Transient analysis of organic electrophosphorescence. II. Transient analysis of triplet-triplet annihilation, PHYSICAL REVIEW B, 10.1103/PhysRevB.62.10967, 62, 16, 10967-10977, 2000.10, In the preceding paper, Paper I [Phys. Rev. B 62, 10 958 (2000)], we studied the formation and diffusion of excitons in several phosphorescent guest-host molecular organic systems. In this paper, we demonstrate that the observed decrease in electrophosphorescent intensity in organic light-emitting devices at high current densities [M. A. Baldo et al., Nature 395, 151 (1998)] is principally due to triplet-triplet annihilation. Using parameters extracted from transient phosphorescent decays, we model the quantum efficiency versus current characteristics of electrophosphorescent devices. It is found that the increase in luminance observed for phosphors with short excited-state lifetimes is due primarily to reduced triplet-triplet annihilation. We also derive an expression for a limiting current density (J(0)) above which triplet-triplet annihilation dominates. The expression for J(0) allows us to establish the criteria for identifying useful phosphors and to assist in the optimized design of electrophosphorescent molecules and device structures.. |
| 201. | Y Okumura, M Nagawa, C Adachi, M Satsuki, S Suga, T Koyama, Y Taniguchi, Low threshold gain-narrowing characteristics of fluorescent styrylbenzene derivatives as a guest molecule in an organic thin-film optical waveguide, CHEMISTRY LETTERS, 10.1246/cl.2000.754, 7, 754-755, 2000.07, We demonstrate that fluorescent styrylbenzene derivatives (SBDs) as a guest molecule (10 mol%) in an organic thin-film optical waveguide show excellent gain-narrowing performance by optical pumping. In particular, an extremely low threshold for gain narrowing is obtained with 4,4'-bis[4-(di-p-tolyl-amino)styryl]biphenyl (LD3). In addition, the incorporation of heterocyclic moieties into the styrylbenzene skeletons results in a higher threshold and also causes no spectral nan owing.. |
| 202. | G Parthasarathy, C Adachi, PE Burrows, Forrest, SR, High-efficiency transparent organic light-emitting devices, APPLIED PHYSICS LETTERS, 76, 15, 2128-2130, 2000.04, We demonstrate organic light-emitting devices (OLEDs) employing highly transparent cathodes comprised of 2,9-dimethyl-4,7 diphenyl-1,10-phenanthroline (BCP) and an ultrathin film of Li capped with radio-frequency magnetron-sputtered indium-tin-oxide. The cathodes are incorporated onto a conventional bilayer small-molecule OLED. The operating voltages and the total device external quantum efficiencies emitted from the top and substrate surfaces (1.0 +/- 0.05)% are comparable to the best conventional undoped OLEDs employing thick metallic cathodes. The device characteristics are independent of the position of Li within the compound cathode, suggesting that Li readily diffuses through BCP to enhance electron injection. An increase of a factor similar to 3.5 in the external quantum efficiency is observed compared to devices containing no Li. These results suggest that Li donates electrons to the BCP, increasing its conductivity to the point that band bending occurs to aid in the injection of charge. (C) 2000 American Institute of Physics. [S0003-6951(00)05015-4].. |
| 203. | H Mochizuki, T Hasui, T Shiono, T Ikeda, C Adachi, Y Taniguchi, Y Shirota, Emission behavior of molecularly doped electroluminescent device using liquid-crystalline matrix, APPLIED PHYSICS LETTERS, 10.1063/1.1309026, 77, 11, 1587-1589, 2000.09, Electroluminescent (EL) behavior has been evaluated in a cell which contained molecular dispersion of 1,4-bis(N,N-diphenylaminophenyl-1,3,4-oxadiazolyl)benzene (OXD) in a low-molecularweight liquid crystal, 4-octyloxy-4'-cyanobiphenyl (8OCB). EL emission was observed above the temperature where the OXD/8OCB mixture showed a liquid-crystalline phase. Furthermore, we fabricated an EL device which consisted of interdigital electrodes coated onto a glass substrate. It was found that the EL emission from the device was highly polarized. (C) 2000 American Institute of Physics. [S0003-6951(00)02937-5].. |
| 204. | C Adachi, MA Baldo, ME Thompson, Forrest, SR, Nearly 100% internal phosphorescence efficiency in an organic light-emitting device, JOURNAL OF APPLIED PHYSICS, 10.1063/1.1409582, 90, 10, 5048-5051, 2001.11, We demonstrate very high efficiency electrophosphorescence in organic light-emitting devices employing a phosphorescent molecule doped into a wide energy gap host. Using bis(2-phenylpyridine)iridium(III) acetylacetonate [(ppy)(2)Ir(acac)] doped into 3-phenyl-4(1'-naphthyl)-5-phenyl-1,2,4-triazole, a maximum external quantum efficiency of (19.0 +/-1.0)% and luminous power efficiency of (60 +/-5) lm/W are achieved. The calculated internal quantum efficiency of (87 +/-7)% is supported by the observed absence of thermally activated nonradiative loss in the photoluminescent efficiency of (ppy)(2)Ir(acac). Thus, very high external quantum efficiencies are due to the nearly 100% internal phosphorescence efficiency of (ppy)(2)Ir(acac) coupled with balanced hole and electron injection, and triplet exciton confinement within the light-emitting layer. (C) 2001 American Institute of Physics.. |
| 205. | BW D'Andrade, MA Baldo, C Adachi, J Brooks, ME Thompson, Forrest, SR, High-efficiency yellow double-doped organic light-emitting devices based on phosphor-sensitized fluorescence, APPLIED PHYSICS LETTERS, 10.1063/1.1388159, 79, 7, 1045-1047, 2001.08, We demonstrate high-efficiency yellow organic light-emitting devices (OLEDs) employing [2-methyl-6-[2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene] propane-dinitrile (DCM2) as a fluorescent lumophore, with a green electrophospho- rescent sensitizer, fac tris(2-phenylpyridine) iridium [Ir(ppy)(3)] co-doped into a 4,4'-N,N(')dicarbazole-biphenyl host. The devices exhibit peak external fluorescent quantum and power efficiencies of 9%+/-1% (25 cd/A) and 17 +/-2 lm/W at 0.01 mA/cm(2), respectively. At 10 mA/cm(2), the efficiencies are 4.1%+/-0.5% (11 cd/A) and 3.1 +/-0.3 lm/W. We show that this exceptionally high performance for a fluorescent dye is due to the similar to 100% efficient transfer of both singlet and triplet excited states in the doubly doped host to the fluorescent material using Ir(ppy)(3) as a sensitizing agent. These results suggest that 100% internal quantum efficiency fluorescent OLEDs employing this sensitization process are within reach. (C) 2001 American Institute of Physics.. |
| 206. | C Adachi, MA Baldo, Forrest, SR, S Lamansky, ME Thompson, RC Kwong, High-efficiency red electrophosphorescence devices, APPLIED PHYSICS LETTERS, 10.1063/1.1355007, 78, 11, 1622-1624, 2001.03, We demonstrate high-efficiency red electrophosphorescent organic light-emitting devices employing bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C-3') iridium(acetylacetonate) [Btp(2)Ir(acac)] as a red phosphor. A maximum external quantum efficiency of eta (ext) = (7.0 +/-0.5)% and power efficiency of eta (p) = (4.6 +/-0.5) lm/W are achieved at a current density of J = 0.01 mA/cm(2). At a higher current density of J = 100 mA/cm(2), eta (ext) = (2.5 +/-0.3)% and eta (p) = (0.56 +/-0.05) lm/W are obtained. The electroluminescent spectrum has a maximum at a wavelength of lambda (max) = 616 nm with additional intensity peaks at lambda (sub) = 670 and 745 nm. The Commission Internationale de L'Eclairage coordinates of (x = 0.68, y = 0.32) are close to meeting video display standards. The short phosphorescence lifetime (similar to4 mus) of Btp(2)Ir(acac) leads to a significant improvement in eta (ext) at high currents as compared to the previously reported red phosphor, 2,3,7,8,12,13,17,18-octaethyl-12H, 23H-prophine platinum (II) PtOEP with a lifetime of similar to 50 mus. (C) 2001 American Institute of Physics.. |
| 207. | C Adachi, RC Kwong, P Djurovich, Adamovich, V, MA Baldo, ME Thompson, Forrest, SR, Endothermic energy transfer: A mechanism for generating very efficient high-energy phosphorescent emission in organic materials, APPLIED PHYSICS LETTERS, 10.1063/1.1400076, 79, 13, 2082-2084, 2001.09, Intermolecular energy transfer processes typically involve an exothermic transfer of energy from a donor site to a molecule with a substantially lower-energy excited state (trap). Here, we demonstrate that an endothermic energy transfer from a molecular organic host (donor) to an organometallic phosphor (trap) can lead to highly efficient blue electroluminescence. This demonstration of endothermic transfer employs iridium(III)bis(4,6-di-fluorophenyl)-pyridinato-N,C-2')picolinate as the phosphor. Due to the comparable energy of the phosphor triplet state relative to that of the 4,4'-N,N-'-dicarbazole-biphenyl conductive host molecule into which it is doped, the rapid exothermic transfer of energy from phosphor to host, and subsequent slow endothermic transfer from host back to phosphor, is clearly observed. Using this unique triplet energy transfer process, we force emission from the higher-energy, blue triplet state of the phosphor (peak wavelength of 470 nm), obtaining a very high maximum organic light-emitting device external quantum efficiency of (5.7 +/-0.3)% and a luminous power efficiency of (6.3 +/-0.3)lm/W. (C) 2001 American Institute of Physics.. |
| 208. | Chihaya Adachi, Raymond Kwong, Stephen R. Forrest, Efficient electrophosphorescence using a doped ambipolar conductive molecular organic thin film, ORGANIC ELECTRONICS, 10.1016/S1566-1199(01)00010-6, 2, 1, 37-43, 2001.03, We demonstrate a high efficiency organic electrophosphorescent device comprised of a 4,4',4 ''-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA) hole transport layer and a 4,4'-N,N'-dicarbazole-biphenyl (CBP) host doped with the metallorganic phosphor, fac-tris(2-phenylpyridine)iridium (Ir(ppy)(3)) as the green light-emitting layer. The device exhibits peak external quantum and power efficiencies of (12.0 +/- 0.6)% and (45 +/- 2) lm/W, respectively, corresponding to similar to 60% internal quantum efficiency. A luminance of 1850 cd/m(2) is observed at a current density of 10 mA/cm(2). The device operating properties are controlled by electron injection into, and transport by the CBP layer along with hole injection from m-MTDATA directly into the Ir(ppy)(3) highest occupied molecular level, leading to direct carrier recombination and exciton formation on the phosphor dopant. Ambipolar conduction properties of the Ir(ppy)(3):CBP layer are established by analysis of triplet-triplet annihilation, exciton formation and the luminance current voltage characteristics. (C) 2001 Published by Elsevier Science B.V.. |
| 209. | C Adachi, ME Thompson, Forrest, SR, Architectures for efficient electrophosphorescent organic light-emitting devices, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, 10.1109/2944.999192, 8, 2, 372-377, 2002.03, We discuss several device architectures leading to high-efficiency organic electrophosphorescent (EP) light emission. An external electroluminescence efficiency (eta(ext)) of (10.0 +/- 0.5)% was realized by doping fac-tris(2-phenylpyridine)iridium (Ir(ppy)(3)) into a 2,9-dimethyl-4,7-diphenyl-1,10-phenenthroline (BCP) electron transport layer. Direct exciton formation on the phosphor dopant avoids exciplex formation at the interface of unipolar hole and electron transport layers. Further, triplet exciton and carrier dynamics in a double heterostructure were investigated to determine the location and width of the exciton formation zone. High-efficiency EP is also demonstrated in a simplified two layer architecture using a 4,4'-N, N'-dicarbazole-biphenyl (CBP) ambipolar carrier transport host.. |
| 210. | D Kolosov, Adamovich, V, P Djurovich, ME Thompson, C Adachi, 1,8-naphthalimides in phosphorescent organic LEDs: The interplay between dopant, exciplex, and host emission, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja0263588, 124, 33, 9945-9954, 2002.08, Four different 1,8-naphthalimide derivatives were examined in phosphorescent organic light emitting diodes (OLEDs), i.e., 1,8-naphthalimide, N-phenyl-1,8-naphthalimide, N-2,6-dibromophenyl-1,8-naphthalimide (niBr), and bis-NN-1,8-naphthalimide. Photoluminescence from all four naphthalimides have violet-blue fluorescence and phosphorescent bands between 550 and 650 nm (visible at 77 K). While all four compounds gave good glassy films when doped with a phosphorescent dopant, only the niBr films remained glassy for extended periods. OLED studies focused on niBr, with two different architectures. One OLED structure (type 1) had the niBr layer as a doped luminescent layer and an undoped niBr layer to act as a hole-blocking layer. The alternate structure (type 2) utilizes a doped CBP layer as the luminescent layer and the niBr layer is used as a hole-blocking layer only (CBP = 4,4'-N,N-dicarbazolylbiphenyl). Type 1 and 2 OLEDs were prepared with green, yellow, and red emissive phosphorescent dopants (lrppy, btlr, and btplr, respectively). The dopants were organometallic lr complexes, previously shown to give highly efficient OLEDs. Of the three dopants, the btplr-based OLEDs showed the best device performance in both structures (peak efficiencies for type 2: 3.2% and 2.3 lum/W at 6.3 V; type 1: 1.7% and 1.3 lm/W at 6.1 V). The green and yellow dopants gave very similar performance in both type 1 and 2 devices (peak efficiencies are 0.2-0.3%), which were significantly poorer than the btplr-based OLEDs. The emission spectrum of the btlr- and btplr-based devices (type 1 and 2) are the same as the solution photoluminescence spectrum of the dopant alone, while the lrppy device gives a broad red emission line (m,, = 640 nm). The red lrppy.niBr emission line is assigned to an lrppy.niBr exciplex. The type 2 lrppy-based device gave a voltage-dependent spectrum, with the red emission observed at low bias (4-8 V), switching over to strong green emission as the bias was raised. All other devices showed bias-independent spectra. Estimates of HOMO, LUMO, and excited-state energies (dopant, niBr, and exciplex) were used to explain the observed spectral properties of these devices. btplr-based devices emit efficiently from isolated dopant states (external efficiencies = 3.2 2.3 lum/W). Irppy-based devices emit only from exciplex states, with low efficiency (external efficiency = 0.3%). btlr.niBr films have very similar energies for the dopant, exciplex, and niBr triplet states, such that relaxation can go through any of these states, leading to low device efficiency (external efficiency = 0.4%). High device efficiency is achieved only when dopant emission is the dominant pathway for relaxation, since exciplex and niBr triplet states give either weak or no electroluminescence.. |
| 211. | T Oyamada, H Tanaka, K Matsushige, H Sasabe, C Adachi, Switching effect in Cu : TCNQ charge transfer-complex thin films by vacuum codeposition, APPLIED PHYSICS LETTERS, 10.1063/1.1600848, 83, 6, 1252-1254, 2003.08, We demonstrate the operation of an organic switching device using a uniform poly-crystalline Cu:7, 7, 8, 8-Tetracyanoquinodimethane (TCNQ) charge transfer (CT)-complex thin film that is prepared by vacuum vapor codeposition. Characteristic CT-absorption at lambda=600-1200 nm was observed in the complex film in the UV-visible spectrum and the cyano stretching peak in the IR spectrum shifted to a higher (more than 29 cm(-1)) wave number than that of a pristine TCNQ film, suggesting the formation of a CT-complex in the evaporated thin film. Reproducible electrical switching characteristics were observed in the indium tin oxide/Al/(Al2O3)/Cu:TCNQ/Al structure. The device exhibited a clear threshold from low impedance to high impedance at an applied voltage of 10.0+/-2.0 V and a reverse phenomenon at a negative bias of -9.5+/-2.0 V. In this study, we demonstrate that a thin Al2O3 layer between the aluminum (Al) anode and Cu:TCNQ layers creates reproducible switching. (C) 2003 American Institute of Physics.. |
| 212. | T Oyamada, C Maeda, H Sasabe, C Adachi, Efficient electron injection characteristics of tetra-2-pyridinylpyrazine (TPP) in organic light emitting diodes, CHEMISTRY LETTERS, 10.1246/cl.2003.388, 32, 4, 388-389, 2003.04, We showed that tetra-2-pyridinylpyrazine (TPP) and TPP: cesium (1:1 molar ratio) composite layers had excellent electron injection and transport characteristics in organic light emitting diodes. High luminescence efficiency with low driving voltage was observed in various cathode configurations, suggesting that the TPP layer can efficiently accept electrons from metal and metal oxide cathode layers, and transport and inject electrons into an adjacent organic layer.. |
| 213. | T Oyamada, C Maeda, H Sasabe, C Adachi, Efficient electron injection mechanism in organic light-emitting diodes using an ultra thin layer of low-work-function metals, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 10.1143/JJAP.42.L1535, 42, 12B, L1535-L1538, 2003.12, To achieve efficient electron injection in organic light-emitting diodes, we examine ultra thin layers (0.50 nm) of the low-work-function metals, Cs (1.9eV), Rb (2.2eV), K (2.3eV), Na (2.4eV), Li (2.9eV), and Ca (2.9eV) capped with aluminum (Al) as a cathode layer. While all the alkali metals show a decrease of driving voltage compared with a single Al cathode, the Cs layer especially shows a significant decrease, and we obtain a high current density of 1.9 A/cm(2) at an applied voltage of only 10V by using this layer. We demonstrate that efficient electron injection is achieved when we use a Cs layer with a thickness of less than 3 nm, although electron injection efficiency abruptly decreases when using a Cs layer thicker than 3 nm. From the Cs thickness dependence of current-voltage characteristics, we conclude that Cs atoms form an alloy layer with aluminum atoms at the organic/Al cathode interface, organic layer/Cs:Al/Al, that significantly enhances electron injection compared with that obtained from bulk Cs layers.. |
| 214. | W Yokoyama, H Sasabe, C Adachi, Carrier injection and transport of steady-state high current density exceeding 1000 A/cm(2) in organic thin films, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 10.1143/JJAP.42.L1353, 42, 11B, L1353-L1355, 2003.11, We demonstrate carrier injection and transport of steady-state high current density into organic thin films. The maximum current density reaches J=1053A/cm(2), the highest ever reported. We employ a 25 nm-thick Copper phthalocyanine (CuPc) thin film sandwiched between an indium-tin-oxide anode and a magnesium-silver alloy cathode with an active electrode dot-size (S) of S=2.0 x 10(-5)cm(2) (radius: r=25mum). We observed that the maximum current density depends on the organic materials used, and the device size and thickness. Decreasing the organic layer thickness significantly changes the current density-voltage (J-V) characteristics, demonstrating that the rate-limiting step of the J-V characteristics changes from the carrier transport process to the carrier injection process. Our achievement of high current density exceeding 1000A/cm(2) in organic thin films is a first step towards the development of organic laser diodes that need extremely high excitation intensity.. |
| 215. | H Mochizuki, T Hasui, M Kawamoto, T Ikeda, C Adachi, Y Taniguchi, Y Shirota, A novel class of photo- and electroactive polymers containing oxadiazole and amine moieties in a side chain, MACROMOLECULES, 10.1021/ma021406u, 36, 10, 3457-3464, 2003.05, A new class of photo- and electroactive polymer materials showing an liquid-crystalline (LC) phase were designed and synthesized: four kinds of polymers with both oxadiazole and arylamine moieties as carrier-transporting groups in the side chain. Among them, the polymers with a dimethylamine and a methylcarbazole moiety show LC phases. Furthermore, all the polymers emitted strong blue fluorescence, and their fluorescent quantum yields were over 0.6. The aligned sample of the polymer with the carbazole moiety emitted polarized fluorescence at room temperature. One-layer type electroluminescent (EL) devices were fabricated by using the polymer with a triphenylamine moiety, which exhibited the highest quantum yield (similar to0.82), and found to emit the EL emission at blue region.. |
| 216. | M Ohkita, C Adachi, M Kawano, T Suzuki, Synthesis and characterization of hexakis(4-pyridylethynyl)benzene and hexakis(5-pyrimidylethynyl)benzene, HETEROCYCLES, 63, 7, 1537-1540, 2004.07, Two new members of snowflake-shaped carbon-rich molecules possessing nitrogen-heterocycles as functional end groups, hexakis(4-pyridylethynyl)benzene (1) and hexakis(5-pyrimidylethynyl)benzene (2), have been prepared by six-fold Sonogashira cross-coupling reaction of hexabromobenzene with 4-ethynylpyridine and 5-ethynylpyrimidine, respectively.. |
| 217. | Y Kawamura, H Sasabe, C Adachi, Simple accurate system for measuring absolute photoluminescence quantum efficiency in organic solid-state thin films, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 10.1143/JJAP.43.7729, 43, 11A, 7729-7730, 2004.11, We accurately measured the absolute photoluminescence (PL) quantum efficiency (eta(PL)) of organic solid-state thin films using an integrating sphere. We particularly measured the eta(PL) of conventional organic materials used in organic light emitting. diodes, such as a tris(8-quinolionolato)aluminum(III) complex (Alq(3)), and a 2 wt%-fac-tris(2-phenylpyridyl)iridium(III): 4,4'-bis(carbazol-9-yl)-2,2'-biphenyl [Ir(ppy)(3):CBP] co-deposited film. Alq(3) and Ir(ppy)(3):CBP showed a eta(PL) = 20 +/- 1% and 97 +/- 2%, which corresponded well to external electroluminescence efficiency using these materials. We also measured their transient PL decay and determined the radiative rate constants with their eta(PL).. |
| 218. | XF Ren, BD Alleyne, PI Djurovich, Tsyba, I, R Bau, ME Thompson, Organometallic complexes as hole transporting materials in organic light-emitting diodes., ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ic035183f, 227, U1439-U1439, 2004.03. |
| 219. | T Oyamada, Y Kawamura, T Koyama, H Sasabe, C Adachi, Formation of europium chelate complexes by vacuum co-deposition and their application in organic light-emitting diodes, ADVANCED MATERIALS, 10.1002/adma.20040090, 16, 13, 1082-+, 2004.07, Europium (Eu) rare-earth complexes, which show intense red photoluminescence (PL) resulting from the f-f transition of Eu 31 ions after the harvesting of both singlet and triplet excitons produced on the surrounding ligands, have been attracting a lot of attention as light-emitting materials for organic light-emitting diodes (OLEDs).([1-28]) Research on the use of Eu complexes to fabricate OLEDs began in 1991 by Kido and colleagues.([1]) An OLED with an emitting layer (EML) made of a Eu(TTA)(3) (TAA: thenoyltrifluoroacetonato) film doped into a poly(methylphenylsilane) (PMPS) host demonstrated a maximum external quantum efficiency (eta(ext)) of 0.01%. In 1994, Tsutsui et al.([3]) reported a eta(ext) of 0.3% obtained with Eu(TTA)(3)phen (phen: 1,10-phenanthroline) used as an EML. Kido et al.([2]) also obtained a eta(ext) of 0.5% with an OLED with a Eu(DBM)(3)phen (DBM: dibenzoylmethanato):2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) (1:3) codeposited film as an EML. Recently, Adachi et al.([15]) reported a eta(ext) of 1.29% obtained with a 1 wt.-% Eu(TTA)(3)phen film doped into a wide-energy-gap 4,4'-N,N'-dicarbazole-biphenyl (CBP) host used as an EML. Most recently, Noto et al.([20]) obtained a eta(ext) of 3.5 % with a 10 wt.-% Eu(DCNP)(DBM)(2)-phen (DCNP: 1,3-dicyano-1,3-propanedione) film doped into a CBP host, and Liang et al.([16,24]) reported a eta(ext) of 5.7 cd A(-1) obtained at a J of 0.04 mA cm(-2) with a 0.6 wt.-% Eu(DBM)(3)-phen film doped into an N,N'-diphenyl-N,N'-di(m-tolyl)benzidine (TPD) host. The efficiency of OLEDs using Eu complexes has been gradually improving over the past decade, which has sparked further interest in the development of Eu-based OLEDs.. |
| 220. | H Nakanotani, H Sasabe, C Adachi, Singlet-singlet and singlet-heat annihilations in fluorescence-based organic light-emitting diodes under steady-state high current density, APPLIED PHYSICS LETTERS, 10.1063/1.1939075, 86, 21, 2005.05, We observed a significant decrease in electroluminescence (EL) in the high-current-density region (J> 1 A/cm(2)) in organic light-emitting diodes (OLEDs). The decreased external quantum efficiency (η(ext)) in an OLED with a cathode diameter of d=50 μ m was in excellent agreement with the singlet-singlet annihilation (SSA) model. In contrast, the decreased η(ext) in an OLED with a cathode diameter of d=1000 μ m coincided well with the singlet-heat annihilation (SHA) model. These results suggest that large OLEDs generate significant Joule heat, which causes additional exciton dissociation in addition to SSA. We also used a very thermally conductive sapphire substrate (46 k/Wm(-1) K-1) combined with a small cathode diameter of 50 μ m in an OLED to alleviate the η(ext) roll off characteristics and achieved injection at a much higher current density. With this device configuration, a maximum current density of J(max)=447 A/cm(2) was achieved. However, decreased η(ext) based on SHA was observed in the high current region, indicating that significant Joule heat was generated under a few hundred A/cm(2) that induced additional exciton dissociation even when the sapphire substrate was used. © 2005 American Institute of Physics.. |
| 221. | T Oyamada, H Uchiuzou, S Akiyama, Y Oku, N Shimoji, K Matsushige, H Sasabe, C Adachi, Lateral organic light-emitting diode with field-effect transistor characteristics, JOURNAL OF APPLIED PHYSICS, 10.1063/1.2060932, 98, 7, 2005.10, We succeeded in observing bright electroluminescence (EL) from 1 wt %-rubrene doped tetraphenylpyrene (TPPy) as an active layer in a lateral organic light-emitting diode structure that allowed field-effect transistor operation. This device configuration provides an organic light-emitting diode structure where the anode (source) and cathode (drain) electrodes are laterally arranged, providing us a chance to control the EL intensity by changing the gate bias. We demonstrated that TPPy provides compatible transistor and EL characteristics. Further, not only rubrene doping into the TPPy host but also adjusting the source-drain channel length significantly improved the EL characteristics. We observed a maximum EL quantum efficiency (eta(ext)) of similar to 0.5% with a Cr/Au source (S)-drain (D) electrode and a slightly higher eta(ext) of similar to 0.8% with S-D electrodes of MgAu/Au, Al/Au, Cr/YAu/Au, and MgAl/Au multilayers, aiming for simultaneous hole and electron injection. (c) 2005 American Institute of Physics.. |
| 222. | H Nakanotani, T Oyamada, Y Kawamura, H Sasabe, C Adachi, Injection and transport of high current density over 1000A/cm(2) in organic light emitting diodes under pulse excitation, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 10.1143/JJAP.44.3659, 44, 6A, 3659-3662, 2005.06, We succeeded in injecting and transporting a maximum high current density of J = 1163 A/cm(2) in organic light-emitting diodes using short-pulse excitation combined with a highly thermally conductive silicon substrate (thermal conductivity: 148W m(-1) K-1) and a small cathode configuration (cathode radius r = 50 pm). A maximum current density almost 20 times higher than that associated with direct current (DC) operation was observed by driving an OLED with a short pulse voltage. With short-pulse excitation, the decrease in external quantum efficiency. (eta(ext)) obeyed a typical singlet-singlet exciton annihilation model well, indicating that the generation of Joule heat in OLEDs can be suppressed under pulse operation.. |
| 223. | M Yoshida, T Tsuchida, T Kurata, M Ikeda, H Sasabe, C Adachi, High-efficiency carrier injection characteristics of dixanthene derivatives in organic light-emitting diodes, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 10.1143/JJAP.44.410, 44, 1A, 410-411, 2005.01, We demonstrate that benzo[1,2,3-kl:4,5,6-k'l']dixanthene (BDX) derivatives show high-efficiency carrier injection in organic light-emitting diodes (OLEDs); Using 3,11-dibromobenzo[1,2,3-kl:4,5,6-k'l']dixanthene (BDX6) as a hole injection layer (HIL), we achieved a low driving voltage of 8.12 +/- 0.10V in obtaining a current density of J = 100mA/cm(2). the hole injection characteristics were superior to those of a device with a conventional CuPc layer as a HIL. On the other hand, inserting benzo[1,2,3-kl:4,5,6-k'l']dixanthene (BDX1) as an electron injection layer (EIL) efficiently decreased driving voltage, indicating a superior electron injection capability compared with a device without a BDX1 ElL. We show that carrier injection efficiency can be well controlled by the substituent groups of BDX, thus providing efficient hole and electron injection layers.. |
| 224. | T Oyamada, H Sasabe, C Adachi, Formation of MgAu alloy cathode by photolithography and its application to organic light-emitting diodes and organic field effect transistors, ELECTRICAL ENGINEERING IN JAPAN, 10.1002/eej.20153, 152, 1, 37-42, 2005.07, To make an efficient electron injection electrode by photolithography, we studied MgAu alloy electrodes, which have a low work function and high resistance to humidity and oxygen. The measured work function of MgAu alloy thin film was 3.7 eV, which is comparable with that of a pure Mg layer and ~0.8 eV lower than that of a pure Au layer. This low work function was maintained even after photolithography, suggesting excellent stability for solvent treatment. Investigating organic field-effect transistor (OFET) characteristics when MgAu alloy comb type source and drain electrodes were used, we successfully obtained n-type FET operation. Furthermore, organic light-emitting diodes (OLEDs) demonstrated the efficient electron injection characteristics of the MgAu alloy cathode, which were similar to those of the conventional MgAg cathode. 2005 Wiley Periodicals, Inc.. |
| 225. | H Yamamoto, H Kasajima, W Yokoyama, H Sasabe, C Adachi, Extremely-high-density carrier injection and transport over 12000 A/cm(2) into organic thin films, APPLIED PHYSICS LETTERS, 10.1063/1.1866230, 86, 8, 2005.02, We achieved extremely-high-density steady state carrier injection and transport at over similar to 10000 A/cm(2) into organic thin films using high thermally conductive substrates, which suppress the temperature rise inside the devices by transferring the joule heat into the substrates. Using a silicon substrate with a high thermal conductivity of 148 W/mK and a small size cathode with a radius of r = 25 mu m, we achieved a maximum current density of J(max) = 12222A/cm(2) and power density of P-max similar to 10(5) W/cm(2) in an ITO(110 nm)/copper phthalocyanine (CuPc) (25 nm)/MgAg(100 nm)/Ag(10 nm) device during a fraction of a second under direct current sweep. Further, we also achieved J(max) = 514 A/cm(2) in a conventional organic light-emitting diode structure using the same techniques. In the CuPc based devices, we observed characteristic current density (J)-voltage (V) behavior, indicating that the J-V characteristics are controlled by the trap-free space-charge-limited cur-rents in the high current region, and by the trapped-charge-limited current in the low current region. (c) 2005 American Institute of Physics.. |
| 226. | T Oyamada, H Sasabe, C Adachi, S Murase, T Tominaga, C Maeda, Extremely low-voltage driving of organic light-emitting diodes with a Cs-doped phenyldipyrenylphosphine oxide layer as an electron-injection layer, APPLIED PHYSICS LETTERS, 10.1063/1.1852707, 86, 3, 2005.01, We demonstrated efficient electron injection and transport in organic light-emitting diodes using an electron-transport layer (ETL) composed of a Cs and phenyldipyrenylphosphine oxide (POPy2) co-deposited layer. In particular, an ETL composed of a CS: POPy2 layer with an atom:molar ratio of 1:2 demonstrated an extremely low driving voltage, resulting in a high current density of 100 mA/cm(2) at an applied voltage of only 3.9 V The results of Kelvin probe and absorption measurements indicated that the formation of a CsAI alloy layer at the CS: POPy2/Al cathode interface and the charge-transfer complex between the Cs and POPy2 contributed to enhancing the efficiency of electron injection and transport, respectively. (C) 2005 American Institute of Physics.. |
| 227. | Yuichiro Kawamura, Hiroyuki Sasabe, Chihaya Adachi, Erratum: Simple accurate system for measuring absolute photoluminescence quantum efficiency in organic solid-state thin films (Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers (2004) 43 (7729)), Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 10.1143/JJAP.44.1160, 44, 2, 1160, 2005.02. |
| 228. | T Oyamada, H Sasabe, C Adachi, S Okuyama, N Shimoji, K Matsushige, Electroluminescence of 2,4-bis(4-(2 '-thiophene-yl)phenyl)thiophene in organic light-emitting field-effect transistors, APPLIED PHYSICS LETTERS, 10.1063/1.1870105, 86, 9, 2005.02, We succeeded in observing electroluminescence (EL) of 2,4-bis(4-(2'-thiophene-yl)phenyl)thiophene (TPTPT) as an active layer in an organic field-effect transistor (OFET). In particular, an OFET with a short channel of d(SD)=0.8 mu m demonstrated higher EL efficiency than one with a much longer channel (d(SD)=9.8 mu m). We observed a maximum EL quantum efficiency (eta(max)) of 6.4 x 10(-3) % in the short-channel-length device at an applied source-drain voltage of V-d=-100 V and a gate voltage of V-g=-40 V. From the OFET characteristics, although the TPTPT layer demonstrated typical p-type operation, the occurrence of EL clearly indicated simultaneous hole and electron injection from the source and drain electronics, respectively, under high V-d and V-g. (C) 2005 American Institute of Physics.. |
| 229. | T Oyamada, H Uchiuzou, H Sasabe, C Adachi, Blue-to-red electroluminescence from organic light-emitting field-effect transistor using various organic semiconductor materials, JOURNAL OF THE SOCIETY FOR INFORMATION DISPLAY, 10.1889/1.2121072, 13, 10, 869-873, 2005.10, We succeeded in observing visible bright electroluminescence from blue to red in an organic field-effect-transistor structure. In particular, tetraphenylpyrene (TPPy) demonstrated a high photoluminescence efficiency of phi(PL)similar to 70% and a maximum electroluminescence efficiency of eta(EL)similar to 10(-2)%. The electroluminescence efficiency (eta(EL)) was enhanced by using a short source-to-drain channel length (L-SD < 1 mu m). In addition, doping the TPPy layer with highly fluorescent rubrene molecules led to an phi(PL) of similar to 100% and a maximum eta(EL) of 0.8%.. |
| 230. | Y Kawamura, K Goushi, J Brooks, JJ Brown, H Sasabe, C Adachi, 100% phosphorescence quantum efficiency of Ir(III) complexes in organic semiconductor films, APPLIED PHYSICS LETTERS, 10.1063/1.1862777, 86, 7, 2005.02, We demonstrate that three Ir(III) complexes used as principal dopants in organic electrophosphorescent diodes have very high photoluminescence quantum efficiency (eta(PL)) in a solid-state film. The green emitting complex, fac-tris(2-phenylpyridinato)iridium(III) [Ir(ppy)(3)], the red-emitting bis[2-(2'-benzothienyl)pyridinato-N,C-3'] (acetylacetonato)iridium(III) [Btp(2)Ir(acac)], and the blue complex bis[(4,6-difluorophenyl)pyridinato-N, C-2](picolinato)iridium(III) (FIrpic) were prepared as codeposited films of varying concentration with 4,4'-bis(N-carbazolyl)-2, 2'-biphenyl, a commonly used host material. The maximum eta(PL) values for Ir(ppy)3, Btp(2)Ir(acac), and FIrpic were, respectively, 97% +/- 2% (at 1.5 mol%), 51% +/- 1% (at 1.4 mol%), and 78% +/- 1% (at 15 mol%). Furthermore, we also observed that the maximum eta(PL) of FIrpic reached 99% +/- 1% when doped into the high triplet energy host, m-bis(N-carbazolyl)benzene, at an optimal concentration of 1.2 mol%. (C) 2005 American Institute of Physics.. |
| 231. | T Aimono, Y Kawamura, K Goushi, H Yamamoto, H Sasabe, C Adachi, 100% fluorescence efficiency of 4,4 '-bis[(N-carbazole)styryl]biphenyl in a solid film and the very low amplified spontaneous emission threshold, APPLIED PHYSICS LETTERS, 10.1063/1.1867555, 86, 7, 2005.02, We examined the amplified spontaneous emission (ASE) characteristics of fluorescent styryl benzene derivatives doped into a 4,4'-di(N-carbazolyl)biphenyl (CBP) host. In particular, 4,4'-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) demonstrated an extremely low ASE threshold of E-th = 0.32 +/- 0.05 muJ/cm(2). We observed that the 6 wt %-BSB-Cz:CBP film has an ultimate photoluminescence (PL) quantum efficiency of Phi(PL) = 100% and a short transient lifetime of tau(f) = 1.0 +/- 0.1 ns, leading to a large radiative decay rate of k(r) = 1 x 10(9) s(-1). We demonstrated that the extremely low ASE threshold originated from the large radiative decay rate of BSB-Cz. (C) 2005 American Institute of Physics.. |
| 232. | T Oyamada, S Akiyama, M Yahiro, M Saigou, M Shiro, H Sasabe, C Adachi, Unusual photoluminescence characteristics of tetraphenylpyrene (TPPy) in various aggregated morphologies, CHEMICAL PHYSICS LETTERS, 10.1016/j.cplett.2005.12.102, 421, 1-3, 295-299, 2006.04, We found that 1,3,6,8-tetraphenylpyrene (TPPy) demonstrates unusual photoluminescence (PL) characteristics in the solid-state morphologies. We investigated the PL characteristics of TPPy in various morphologies including powder, deposited film, and solutions. The TPPy powder (A), which was prepared through column chromatography, recrystallization, and train sublimation, showed blue fluorescence with a peak of maximum wavelength of = 451 nm. The TPPy powder (B), which was obtained by thermal annealing of TPPy powder (A) in a quartz tube in nitrogen, showed green fluorescence with gimel(max) = 510 nm. Furthermore, the TPPy powder (B) was reversibly converted into TPPy powder (A) by recrystallization. We conclude that TPPy dimers form locally in the TPPy monomer aggregates during thermal annealing and redissociate into the monomer states during recrystallization. (c) 2006 Elsevier B.V. All rights reserved.. |
| 233. | John A. Mikroyannidis, Larysa Fenenko, Chihaya Adachi, Synthesis and photophysical characteristics of 2,7-fluorenevinylene-based trimers and their electroluminescence, JOURNAL OF PHYSICAL CHEMISTRY B, 10.1021/jp0631477, 110, 41, 20317-20326, 2006.10, Three new 2,7-fluorenevinylene-based trimers were synthesized and characterized. The synthesis was carried out by the Heck coupling reaction of 9,9-dihexyl-2,7-divinylfluorene with 2-(4-bromophenyl-5-phenyl-1,3,4-oxadiazole, N,N-diphenyl-4-bromoaniline, or 3-bromopyrene to afford the trimers OXD, TPA, and PYR, respectively. All the trimers were readily soluble in common organic solvents such as tetrahydrofuran, dichloromethane, chloroform, and toluene. Their glass transition temperatures ranged from 33 to 60 C. The UV-vis spectra showed an absorption maximum at lambda(a,max) = 379-417 nm with optical band gap of E-g = 2.47-2.66 eV. In solution, they emitted strong blue-green photoluminescence (PL) with PL maximum at If, max) 455-565 nm and fluorescence quantum yield of Phi(f) = 0.65-0.74. On the other hand, in their spin-coated films, the PL efficiencies significantly decreased due to the presence of concentration quenching. All samples showed nanosecond transient lifetime containing two components, suggesting excimer formation. The organic light-emitting diodes (OLEDs) with OXD and TPA showed green emission with electroluminescence (EL) quantum efficiencies of eta(EL) similar to 10(-2)%, while very weak EL efficiency of eta(EL) similar to 10(-5)% was observed with PYR. The highest occupied molecular orbital (HOMO) levels of the films were found to be 5.05-5.75 eV.. |
| 234. | Takahito Oyamada, Guang Shao, Hiroyuki Uchiuzou, Hajime Nakanotani, Akihiro Orita, Junzo Otera, Masayuki Yahiro, Chihaya Adachi, Optical and electrical properties of bis(4-(phenylethynyl)phenyl)ethynes and their application to organic field-effect transistors, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 10.1143/JJAP.45.L1331, 45, 46-50, L1331-L1333, 2006.12, We demonstrate that bis(4-(phenylethynyl)phenyl)ethynes (BPEPEs) have high potential as organic field-effect transistors (FETs). We observed a p-type transistor operation in FETs with BPEPE derivatives having electron-donating substituents. The devices showed FET hole mobilities in the range of mu(eta) = 10(-3)-10(-5) cm(2)/(V s), depending on the substituents. Further, bis(4(4-trifluoromethylphenylethynyl)phenyl)ethyne (4-CF3-BPEPE), which has an electron-withdrawing group, indicated n-type operation.. |
| 235. | Atsushi Takahashi, Ayataka Endo, Chihaya Adachi, Novel electron-transporting carbazolylphenylquinolines for phosphorescent organic light-emitting diodes, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 10.1143/JJAP.45.9228, 45, 12, 9228-9230, 2006.12, We developed four types of novel electron-transporting carbazolylphenyl-quinoline (CQ) derivatives. The photophysical and thermal properties of these materials were studied. Moreover, these materials were applied for an electron-transport layer and for a host material in phosphorescent organic light-emitting diodes, and a high electroluminescence (EL) efficiency was obtained in these devices. With 2-(3-(3,6-diphenylcarbazole-9-yl)phenyl)lepidine (DPCLP) as a host and tris(2-phenylpyridine)iridium(III) [lr(PPY)3] as a guest, the highest EL efficiency of eta(ext) = 11.2% was obtained.. |
| 236. | John A. Mikroyannidis, Helen A. Moshopoulou, John A. Anastasopoulos, Minas M. Stylianakis, Larysa Fenenko, Chihaya Adachi, Novel blue-greenish electroluminescent poly(fluorenevinylene-alt- dibenzothiophenevinylene)s and their model compounds, Journal of Polymer Science, Part A: Polymer Chemistry, 10.1002/pola.21753, 44, 23, 6790-6800, 2006.12, Poly(9,9-dihexylfluorene-2,7-vinylene-alt-dibenzothiophene-2,8-vinylene) (PS) and poly(9,9-dihexylfluorene-2,7-vinylene-alt-dibenzothiophene-5,5-dioxide- 2,8-vinylene) (PSO) as well as corresponding model compounds were synthesized by Heck coupling. Both the polymers and model compounds were readily soluble in common organic solvents such as tetrahydrofuran, dichloromethane, chloroform, and toluene. The polymers showed a decomposition temperature at ∼430°C and a char yield of about 65% at 800°C in N2. The glass-transition temperatures of the polymers were almost identical (75-77°C) and higher than those of the model compounds (26-45°C). All samples absorbed around 390 nm, and their optical band gaps were 2.69-2.85 eV. They behaved as blue-greenish light emitting materials in both solutions and thin films, with photoluminescence emission maxima at 450-483 nm and photoluminescence quantum yields of 0.52-0.72 in solution. Organic light-emitting diodes with an indium tin oxide/ poly(ethylene dioxythiophene):poly(styrene sulfonic acid)/polymer/Mg:Ag/Ag configuration with polymers PS and PSO as emitting layers showed green electroluminescence with maxima at 530 and 540 nm, respectively. © 2006 Wiley Periodicals, Inc.. |
| 237. | H Yamamoto, T Oyamada, W Hale, S Aoshima, H Sasabe, C Adachi, Low-damage indium tin oxide formation on organic dyers using unique cylindrical sputtering module and application in transparent organic light-emitting diodes, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 10.1143/JJAP.45.L213, 45, 4-7, L213-L216, 2006.02, We demonstrate a low-damage technique for forming an indium tin oxide (ITO) layer on an organic layer by using a unique cylindrical sputtering module and the fabrication of high-performance transparent organic light-emitting diodes (TOLEDs). The ITO target has an off-axis alignment to the substrate, and it confines plasma to the inside of the module, thereby forming ITO with little damage to the underlying organic layers. We found that the composition ratio of In 203 (90%) and SnO2 (10%) in the deposited film is the same as the target composition ratio, and that the composition ratio distribution was spatially uniform, showing no angular dependence. We fabricated an ITO [110nm]/4,4'-bis[N(1-naphthyl)-N-phenyl-amino]biphenyl (alpha-NPD) [50 nm]/tris-(8-hydroxy-quinoline)aluminum (Alq(3)) [30 nm]/Cs:phenyldipyrenylphosphine oxide (POPy2) [20 nm]/ ITO [100nm] device, using a cylindrical target for the top ITO cathode fabrication. The device showed excellent J-V characteristics, with a current density of J = 883 mA/cm(2) at an applied voltage of 10V and a maximum external quantum efficiency of eta(ext) = 0.76%.. |
| 238. | Y Kawamura, J Brooks, JJ Brown, H Sasabe, C Adachi, Intermolecular interaction and a concentration-quenching mechanism of phosphorescent Ir(III) complexes in a solid film, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.96.017404, 96, 1, 017404, 2006.01, Solid-state self-quenching processes of highly efficient Ir(III) phosphorescent emitters are investigated by the measurement of thin film photoluminescence quantum efficiency and transient lifetime as a function of doping concentration in a host matrix. The radiative decay rate constant is found to be independent from the average distance between dopant molecules (R), and the concentration-quenching rate constant is shown to be dependent on R-6. The quenching dependence on R strongly suggests that luminescent concentration quenching in a phosphorescent Ir(III) complex:host film is controlled by dipole-dipole deactivating interactions as described by the Forster energy transfer model.. |
| 239. | Jun-ichi Nishide, Takahito Oyamada, Seiji Akiyama, Hiroyuki Sasabe, Chihaya Adachi, High field-effect mobility in an organic thin-film transistor with a solid-state polymerized polydiacetylene film as an active layer, ADVANCED MATERIALS, 10.1002/adma.200601419, 18, 23, 3120-+, 2006.12, A highly ordered polydiacetylene thin film was prepared by vacuum deposition of 10,12-pentacosadiynoic acid, followed by photopolymerization of this layer under UV irradiation. Using an optimum substrate temperature of 50 degrees C during the monomer deposition, we obtained a high field-effect hole mobility of 0.8 cm(2) V-1 s(-1) with p-type field-effect transistor characteristics in the top source-drain electrode configuration.. |
| 240. | Toshinori Matsushima, Chihaya Adachi, Extremely low voltage organic light-emitting diodes with p-doped alpha-sexithiophene hole transport and n-doped phenyldipyrenylphosphine oxide electron transport layers, APPLIED PHYSICS LETTERS, 10.1063/1.2410236, 89, 25, 2006.12, Organic light-emitting diodes with p-doped alpha-sexithiophene and n-doped phenyldipyrenylphosphine oxide carrier transport layers are fabricated. In the doped diodes, the authors demonstrate an extremely low driving voltage of 2.9 V at a current density of 100 mA/cm(2) and very high luminance at a low driving voltage: 1000 cd/m(2) at 2.4 V, 10 000 cd/m(2) at 2.8 V, and 920 000 cd/m(2) at 4.5 V. Such lowered driving voltages and enhanced luminance characteristics are attributed to the generation of free charge carriers by charge transfer from matrix to dopant molecules, resulting in an increase in electrical conductivities and formation of Ohmic contacts at metal/organic interfaces. (c) 2006 American Institute of Physics.. |
| 241. | T Oyamada, H Sasabe, Y Oku, N Shimoji, C Adachi, Estimation of carrier recombination and electroluminescence emission regions in organic light-emitting field-effect transistors using local doping method, APPLIED PHYSICS LETTERS, 10.1063/1.2181629, 88, 9, 2006.02, To elucidate the electroluminescence (EL) mechanism of organic light-emitting field-effect transistors (OLEFETs), we determined the carrier recombination and EL emission regions using the local doping method. We demonstrated that the local doping method is a useful technique for estimating the width of these regions in OLEFETs. We inserted an ultrathin rubrene doped 1,3,6,8-tetraphenylpyrene (TPPy) layer (d=10 nm) as a sensing layer in a TPPy layer (80 nm) and measured the luminance-drain current-drain voltage characteristics and the EL spectra depending on the position of the sensing layer. We confirmed that the EL emission region expanded almost to the height (h similar or equal to 40 nm) of the source-drain electrodes and was independent of the gate bias voltage (V-g). Further, we observed that the EL external quantum efficiency (eta(ext)) significantly decreased as V-g increased, suggesting that excitons generated in a TPPy host layer by carrier recombination are quenched by the application of V-g.. |
| 242. | T Matsushima, H Sasabe, C Adachi, Carrier injection and transport characteristics of copper phthalocyanine thin films under low to extremely high current densities, APPLIED PHYSICS LETTERS, 10.1063/1.2165197, 88, 3, 2006.01, We investigated current density-voltage (J-V) characteristics of copper phthalocyanine (CuPc) thin films depending on active device areas. We prepared CuPc thin-film devices with active areas smaller than S=625 mu m(2) using a photolithography technique. The maximum breakdown current density (J(MAX)) and voltage (V-MAX) of the devices markedly increased as the active area was decreased from S=625 to 7.9 mu m(2). In the smallest device, with S=7.9 mu m(2), we obtained not only an extremely high current density of J(MAX)=128 kA/cm(2) at V-MAX=9.2 V, but also unique J-V characteristics, indicating that the carrier conduction process shifted from the Fowler-Nordheim tunneling injection mechanism to shallow-trap and trap-free space-charge-limited current mechanisms.. |
| 243. | Hajime Nakanotani, Naoki Matsumoto, Hiroyuki Uchiuzou, Masakazu Nishiyama, Masayuki Yahiro, Chihaya Adachi, Very low amplified spontaneous emission threshold and electroluminescence characteristics of 1,1 '-diphenyl substituted fluorene derivatives, OPTICAL MATERIALS, 10.1016/j.optmat.2007.02.045, 30, 4, 630-636, 2007.12, A blue amplified spontaneous emission with a very low threshold was observed in novel fluorene derivatives doped into a 4,4'-bis-(N-carbazole)-biphenyl (CBP) host. With 6wt%-2,7-bis[4'-(N,N-diphenylamino)-1,1'-biphenyl-4-yl]-9,9-bis(1,1'-biphenyl-4-yl)-9H-fluorene (BDF2) or 2,7-bis[1,1'-biphenyl-4-yl]-9,9-bis(1,1'-biphenyl-4-yl)-9-H-fluorene (BBF) as a dopant, high photoluminescence quantum efficiencies of 90% +/- 1% and 78% +/- 2% with extremely low amplified spontaneous emission thresholds of 0.15 +/- 0.05 mu J/cm(2) (300 W/cm(2)) and 0.17 +/- 0.04 mu J/cm(2) (340 W/cm(2)) were obtained. We also observed a high gain coefficient (38 cm(-1)) and a low loss coefficient (6 cm(-1)) in a 6 wt%-BDF2:CBP thin film optical-waveguide. Furthermore, an organic light emitting diode with BDF2 as an emitter demonstrated a high external quantum efficiency (eta(ext)) of 4.5% +/- 0.1%. In addition, electroluminescence from an organic field-effect transistor with BDF2 as an active material was also observed with a maximum eta(ext) of 0.02%. (c) 2007 Elsevier B.V. All rights reserved.. |
| 244. | Takahito Oyamada, Yuhsuke Sugawara, Yuhki Terao, Hiroyuki Sasabe, Chihaya Adachi, Top light-harvesting organic solar cell using ultrathin Ag/MgAg layer as anode, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 10.1143/JJAP.46.1734, 46, 4A, 1734-1735, 2007.04, We fabricate a top light-harvesting organic solar cell (TL-OSC) with a Si substrate/SiO2 layer/cathode/organic layer/semitransparent metal anode structure. We obtain power conversion efficiency (eta(p)) comparable to that of conventional bottom-type OSCs. To harvest light from a top anode, we use a 1 nm Ag layer/4 nm MgAg layer having a transmittance of 55 - 80% in the visible and near-infrared regions. We also insert an ultrathin molybdenum oxide (MoO3) layer at the cathode/organic layer interface to increase hole collection efficiency from the organic layer into the cathode.. |
| 245. | Hajime Nakanotani, Chihaya Adachi, Sadayuki Watanabe, Ryuzi Katoh, Spectrally narrow emission from organic films under continuous-wave excitation, APPLIED PHYSICS LETTERS, 10.1063/1.2746958, 90, 23, 2007.06, The authors observed a narrow emission from a 500-nm-thick codeposited organic thin film, 6 wt % 4,4(')-bis[(N-carbazole)styryl]-biphenyl (BSB-Cz) doped into a 4,4(')-bis(N-carbazole)-biphenyl host, under continuous-wave excitation. Although they observed no clear threshold characteristics on the spectral narrowing, they found that the emission centered at a wavelength of lambda(ASE)=462 nm, corresponding to the zero to one transition of BSB-Cz, has a transverse electric mode with a narrow full width at half maximum of lambda(FWHM)=3.4 nm, indicating the occurrence of amplified spontaneous emission. No excited state absorptions of singlet and triplet excited states of BSB-Cz are confirmed around lambda(ASE), leading to large net gain for the light amplification. (c) 2007 American Institute of Physics.. |
| 246. | Daisuke Yokoyama, Hajime Nakanotani, Yousuke Setoguchi, Masato Moriwake, Dai Ohnishi, Masayuki Yahiro, Chihaya Adachi, Spectrally narrow emission at cutoff wavelength from edge of electrically pumped organic light-emitting diodes, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 10.1143/JJAP.46.L826, 46, 33-35, L826-L829, 2007.09, We demonstrate spectrally narrow emissions from the edge of electrically pumped organic light-emitting diodes having a fine "line-shaped" waveguide structure with a silver cathode. A 4,4'-bis[(N-carbazole)styryl]-biphenyl (BSB-Cz) layer, which has a very low amplified spontaneous emission threshold, was used as an emitting layer. We observed extremely narrow emissions having polarized transverse electric (TE) mode. The full width at half maximum became narrower down to 6.5 nm as the peak wavelength of the emission approached the wavelength of the 0-1 transition of the BSB-Cz layer. The edge emission intensity showed a superlinear relationship with the current density, and the spectral shapes changed appreciably depending on the current density, indicating the occurrence of amplification of the emitted light. The peak wavelengths of the edge emissions were attributed to the leaky mode very close to the cutoff wavelength of the waveguide structure having the metal cladding layer.. |
| 247. | Takahito Oyamada, Chih-Hao Chang, Teng-Chih Chao, Fu-Chuan Fang, Chung-Chih Wu, Ken-Tsung Wong, Hiroyuki Sasabe, Chihaya Adachi, Optical properties of oligo(9,9-diarylfluorene) derivatives in thin films and their application for organic light-emitting field-effect transistors, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp0654056, 111, 1, 108-115, 2007.01, We demonstrated that oligo(9,9-diarylfluorene) derivatives have high potential for optoelectronic applications such as organic lasers and light-emitting organic field-effect transistors (LE-OFETs). The oligo(9,9diarylfluorene) derivatives have high photoluminescence quantum efficiencies up to Phi(PL) approximate to 70-75% and very low amplified spontaneous emission thresholds (E-th) down to 0.5 AJ/cm(2) in their vacuum-deposited neat films. In particular, the trimer derivatives (B3 and T3) show higher PL and lower Eth than those of the dimers (B2 and T2). Efficient deep-blue LE-OFETs with the electroluminescence (EL) peaking at lambda(peak) = 429 nm were demonstrated using the ter(9,9-diarylfluorene) as the active layer. Rather high luminance up to L approximate to 150 cd/m(2) and EL quantum efficiency up to eta(ext) approximate to 0.60% were achieved with the optimum source-drain channel length, indicating bipolar carrier injection in the terfluorene layer under the FET operation.. |
| 248. | Toshinori Matsushima, Chihaya Adachi, Observation of extremely high current densities on order of MA/cm(2) in copper phthalocyanine thin-film devices with submicron active areas, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 10.1143/JJAP.46.L1179, 46, 45-49, L1179-L1181, 2007.12, Using contact photolithography and electron-beam lithography techniques, we manufactured copper phthalocyanine thin-film devices with active areas ranging from 1,000,000 to 0.04 mu m(2) to investigate how much current can flow through these devices with the aim of fabricating electrically pumped organic laser diodes. From the results of our current density-voltage (J-V) measurements, we found that the device with the smallest active area of 0.04 mu m(2) on a silicon substrate exhibits an extremely high current density of 6,350,000 A/cm(2) due to improved thermal management. The J-V characteristics of the devices are controlled by shallow-trap space-charge-limited current (SCLC), trap-free SCLC, and two-carrier injection current mechanisms over a wide range of current densities between nA/cm(2) and MA/cm(2).. |
| 249. | Masaki Aonuma, Takahito Oyamada, Hiroyuki Sasabe, Tetsuzou Miki, Chihaya Adachi, Material design of hole transport materials capable of thick-film formation in organic light emitting diodes, APPLIED PHYSICS LETTERS, 10.1063/1.2733627, 90, 18, 2007.04, In this study, the authors show an empirical guideline for designing hole transport materials (HTMs) that suppress rises in driving voltage even with a few hundred nanometer thick film in the organic light emitting diodes (OLEDs). In a device structure of indium tin oxide (110 nm)/hole transport layer (HTL) (X nm)/4,4(')-N,N-'-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (10 nm)/tris-(8-hydroxyquinoline)aluminum (Alq(3)) (50 nm)/MgAg (100 nm)/Ag (10 nm), the authors compared electroluminescence characteristics of the OLEDs having a thin-film HTL (X=50 nm) and a thick-film HTL (X=300 nm) using 13 kinds of HTMs. They observed a closed correlation between suppression of the driving voltage and the HTMs' thermal characteristics. Highly thermally stable HTMs resulted in a small increase in the driving voltage. (c) 2007 American Institute of Physics.. |
| 250. | Larysa Fenenko, Chihaya Adachi, Influence of heat treatment on indium-tin-oxide anodes and copper phthalocyanine hole injection layers in organic light-emitting diodes, THIN SOLID FILMS, 10.1016/j.tsf.2006.11.116, 515, 11, 4812-4818, 2007.04, Modifications of indium-tin-oxide (ITO) and copper phthalocyanine (CuPc) layers by heat treatment aimed at lowering driving voltage in organic light-emitting diodes (OLEDs) are examined. Significant changes were observed in the surface morphology and carrier injection properties of ITO and CuPc layers after annealing at T=250 degrees C for 0-60 min in a glove box. In the case of ITO annealing, although the ITO work function gradually decreased and the surface of the ITO layer became smoother than that of an unannealed ITO layer, we observed an appreciable decrease in the driving voltage with an increase in annealing time. In the case of CuPc annealing, on the other hand, we observed deterioration of the OLED's characteristics. All devices demonstrated an increase in driving voltage due to the pronounced crystallization of the CuPc layer. (c) 2006 Elsevier B.V. All rights reserved.. |
| 251. | Hiroshi Kanno, Kaori Ishikawa, Yoshitaka Nishio, Ayataka Endo, Chihaya Adachi, Kenichi Shibata, Highly efficient and stable red phosphorescent organic light-emitting device using bis[2-(2-benzothiazoyl)phenolato]zinc(II) as host material, APPLIED PHYSICS LETTERS, 10.1063/1.2643908, 90, 12, 2007.03, The red-emitting phosphorescent organic light-emitting device employing Bis[2-(2-benzothiazoyl)phenolato]zinc(II) (Zn(BTP)(2)) as a host material has been demonstrated. The device generates saturated red emission with Commission Internationale de l'Eclairage coordinates of (0.67, 0.33), characterized by a low driving voltage of 3.2 V and high external quantum efficiency of 10.3% at 10 mA/cm(2). Moreover, the efficiency and lifetime are improved by using 30% NPB-doped Zn(BTP)(2) host in the emitting layer, where NPB is 4,4(')-bis(N-phenyl-1-naphthyl-amino)biphenyl. The maximum external quantum efficiency of the device reaches 12.6% at 1.7 mA/cm(2). The device has exhibited excellent stability. The half-luminance lifetime is 240 h at 80 mA/cm(2) (initial luminance of 6070 cd/m(2)). The relationship between the employed host material and device performance is discussed. (c) 2007 American Institute of Physics.. |
| 252. | Toshinori Matsushima, Chihaya Adachi, High-current injection and transport on order of kA/cm(2) in organic light-emitting diodes having mixed organic/organic heterojunction interfaces, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 10.1143/JJAP.46.L861, 46, 33-35, L861-L863, 2007.09, We manufactured multilayer organic light-emitting diodes (OLEDs) with mixed organic/organic heterojunction interfaces composed of alpha-sexithiophene and phenyldipyrenylphosphine oxide carrier-transporting layers. In the mixed-interface OLEDs, we achieved a low driving voltage of 3.6 V at a current flow of 100 mA/cm(2), which was caused by efficient carrier injection at the mixed interfaces. We investigated how much current can flow through these OLEDs with the aim of fabricating electrically pumped organic laser diodes. We found that an OLED of this type with a small active area of 625 mu m(2) on a high-thermal-conductivity sapphire substrate can sustain high current densities of 1.1 kA/cm(2) and emits bright electroluminescence of 7.9 Mcd/m(2) under direct current.. |
| 253. | Hajime Nakanotani, Seiji Akiyama, Dai Ohnishi, Masato Moriwake, Masayuki Yahiro, Toshitada Yoshihara, Seiji Tobita, Chihaya Adachi, Extremely low-threshold amplified spontaneous emission of 9,9 '-spirobifluorene derivatives and electroluminescence from field-effect transistor structure, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.200700069, 17, 14, 2328-2335, 2007.09, By doping 2,7-bis[4-(N-carbazole)phenylvinyl]-9,9'-spirobifluorene (spiro-SBCz) into a wide energy gap 4,4'-bis(9-carbazole)-2,2'-biphenyl (CBP) host, we demonstrate an extremely low ASE threshold of E-th = (0.11 +/- 0.05) mu J cm(-2) (220 W cm(-2)) which is the lowest ASE threshold ever reported. In addition, we confirmed that the spiro-SBCz thin film functions as an active light emitting layer in organic light-emitting diode (OLED) and a field-effect transistor (FET). In particular, we succeeded to obtain linear electroluminescence in the FET structure which will be useful for future organic laser diodes.. |
| 254. | Toshinori Matsushima, Masayuki Yahiro, Chihaya Adachi, Estimation of electron traps in carbon-60 field-effect transistors by a thermally stimulated current technique, APPLIED PHYSICS LETTERS, 10.1063/1.2779240, 91, 10, 2007.09, The authors investigated the influence of O-2 and H2O molecules absorbed in carbon-60 (C60) films on their electron trap and n-type field-effect transistor (FET) characteristics. Electron traps in the C60 films were directly measured using a thermally stimulated current (TSC) technique. The TSC results demonstrate that the absorption of O-2 and H2O molecules in the C60 films induced an increase in the electron trap concentration, which degrades C60 FET characteristics. By annealing the C60 films at 100 degrees C for 8 h, the electron trap concentrations were markedly lowered, enhancing the C60 FET characteristics. An electron mobility of 0.017 cm(2)/V s and a current on/off ratio of 10(6) were observed from the degassed C60 FETs. (C) 2007 American Institute of Physics.. |
| 255. | Larysa Fenenko, Guang Shao, Akihiro Orita, Masayuki Yahiro, Junzo Otera, Sergei Svechnikov, Chihaya Adachi, Electrical properties of 1,4-bis(4-(phenylethynyl)phenylethynyl)benzene and its application for organic light emitting diodes, CHEMICAL COMMUNICATIONS, 10.1039/b700466d, 22, 2278-2280, 2007.06, We found that a phenylene ethynylene derivative, 1,4-bis(4-(phenylethynyl)phenylethynyl)benzene (BPPB), provides very high photoluminescence efficiency both in solution (Phi(PL) = 95 +/- 3%) and thin films (Phi(PL) = 71 +/- 3%); further, we observed blue electroluminescence (EL) of lambda(EL (max)) similar to 470 and 510 nm with an external EL efficiency of eta(EL) similar to 0.53% and maximum luminance of similar to 70000 cd m(-2) at current density of similar to 2 A cm(-2) with BPPB as an emitter; also we identified that BPPB functions as a hole transport layer in organic light emitting diodes.. |
| 256. | Yuhki Terao, Hiroyuki Sasabe, Chihaya Adachi, Correlation of hole mobility, exciton diffusion length, and solar cell characteristics in phthalocyanine/fullerene organic solar cells, APPLIED PHYSICS LETTERS, 10.1063/1.2711525, 90, 10, 2007.03, The authors investigated heterojunction organic solar cells composed of different metal phthalocyanines (MPcs, M=Fe, Co, Ni, Cu, and H-2)/fullerene (C-60) and compared the solar cell characteristics with the field-effect hole mobilities (mu(h)) and exciton diffusion length (L-ex) of the different MPcs. They observed that the short circuit current (J(SC)) is linearly dependent on the mu(h) of the MPcs, except for ZnPc. They also estimated the L-ex of the MPcs by creating a line of best fit using the action spectra of the external quantum efficiency in the solar cells and found that J(SC) is closely correlated with the L-ex of the MPcs. (c) 2007 American Institute of Physics.. |
| 257. | Toshinori Matsushima, Kenichi Goushi, Chihaya Adachi, Charge-carrier injection characteristics at organic/organic heterojunction interfaces in organic light-emitting diodes, CHEMICAL PHYSICS LETTERS, 10.1016/j.cplett.2007.01.010, 435, 4-6, 327-330, 2007.02, Organic light-emitting diodes (OLEDs) having various guest molecules doped in an organic host matrix layer are fabricated [the OLED structure is anode/hole-transporting layer (HTL)/guest-host emitting layer/hole-blocking layer/electron-transporting layer/cathode], and the dependence of current density-voltage (J-V) characteristics of the OLEDs on highest occupied molecular orbital (HOMO) levels of guest molecules are investigated. From the J-V characteristics of these OLEDs, we find two important results: (1) J-V characteristics of the OLEDs are controlled by the direct hole injection from the neighboring HTL to guest molecules, and (2) HOMO level alignment between the HTL and guest molecules provides efficient hole injection at this interface. (c) 2007 Elsevier B.V. All rights reserved.. |
| 258. | Makoto Nakahara, Masahiro Minagawa, Takahito Oyamada, Toyoyasu Tadokoro, Hiroyuki Sasabe, Chihaya Adachi, Analysis of carrier traps in continuously operated 4,4'-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl/tris(8-hydroxyquinoline)aluminum-based organic light-emitting diodes by thermally stimulated current measurement, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 10.1143/JJAP.46.L636, 46, 25-28, L636-L639, 2007.07, We measured the reliability of two different organic light-emitting diodes (OLEDs) composed of indium tin oxide (ITO)/4,4 '-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (alpha-NPD)/tris(8-hydroxyquinoline)aluminum (Alq(3))/MgAg (two layer) or ITO/ alpha-NPD/alpha-NPD:Alq(3) (mixed layer)/Alq(3)/MgAg. Changes in the carrier trap distribution were estimated by thermally stimulated current (TSC) measurements. Improved device reliability was observed in the mixed-layer device. In the case of the two layer device, the TSC peaks gradually changed depending on. the duration of continuous operation, while the mixed device showed no change in its TSC spectra. These spectral differences indicate that the mixing of alpha-NPD and Alq(3) occurs during the continuous operation in the two-layer device.. |
| 259. | Tomo Sakanoue, Masayuki Yahiro, Chihaya Adachi, Hiroyuki Uchiuzou, Takayoshi Takahashi, Akio Toshimitsu, Ambipolar light-emitting organic field-effect transistors using a wide-band-gap blue-emitting small molecule, APPLIED PHYSICS LETTERS, 10.1063/1.2734389, 90, 17, 2007.04, The authors applied a wide-band-gap (2.9 eV) molecule of 4,-4(')-bis(styryl)biphenyl (BSBP) as an active layer in light-emitting organic field-effect transistors. They found that BSBP provided both relatively high field-effect hole mobility of 0.01 cm(2)/V s and photoluminescence efficiency of 20% in thin film. They achieved ambipolar operation by without breaking vacuum through devices' preparation and measurements, applying aluminum contacts, and inserting a hydroxyl-free poly(methylmethacrylate) layer, and light emission was observed when the device was operated in the ambipolar mode. The results presented here will open the way to fabricating efficient light-emitting transistors with high mobility. (c) 2007 American Institute of Physics.. |
| 260. | Satria Zulkarnaen Bisri, Tetsuo Takahashi, Taishi Takenobu, Masayuki Yahir, Chihaya Adachi, Yoshihiro Iwasa, Ambipolar field-effect transistor of high photoluminescent material tetraphenylpyrene (TPPy) single crystal, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 10.1143/JJAP.46.L5961, 46, 20-24, L596-L598, 2007.06, An ambipolar field-effect transistor (FET) based on a 1,3,6,8-tetraphenylpyrene (TPPy) single crystal, a highly photoluminescent material, has been successfully fabricated. Several kinds of metal electrodes have been employed to investigate the charge injection characteristics into the single-crystal FET. Hole and electron mobilities of 0.34 and 7.7 x 10(-2) cm(2)/(V center dot s) were achieved using Au and Ca electrodes, respectively. The ambipolar characteristic of this device gives a prospect for further development in light-emitting FET operation.. |
| 261. | Hajime Nakanotani, Masayuki Yahiro, Chihaya Adachi, Koki Yano, Ambipolar field-effect transistor based on organic-inorganic hybrid structure, APPLIED PHYSICS LETTERS, 10.1063/1.2752023, 90, 26, 2007.06, The authors developed an ambipolar field-effect transistor (FET) based on an organic-inorganic hybrid structure that consisted of an indium zinc oxide and pentacene double layer fabricated on a SiO2/n(++)-Si substrate. Although the FETs based on an indium zinc oxide or pentacene single layer only showed unipolar FET characteristics, the hybrid FET showed definite ambipolar FET characteristics. The authors obtained a highly saturated field-effect hole and electron mobilities of 0.14 and 13.8 cm(2)/V s. Furthermore, the authors demonstrated electroluminescence from hybrid FETs using tetracene as an emitting layer. The authors' success shows that the hybridization of organic and inorganic materials opens up a new field in electronics. (c) 2007 American Institute of Physics.. |
| 262. | John A. Mikroyannidis, Larysa Fenenko, Masayuki Yahiro, Chihaya Adachi, Alternating copolyfluorenevinyles with polynuclear aromatic moieties: Synthesis, photophysics, and electroluminescence, JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY, 10.1002/pola.22213, 45, 20, 4661-4670, 2007.10, Three new copolymers, namely poly(fluorenevinylene-alt-naphthalenevinylene) (N), poly(fluorenevinylene-alt-anthracenevinylene) (A) and poly(fluorenevinylene-alt-pyrenevinylene) (P), were synthesized by Heck coupling of 9,9-dihexyl-2,7-divinylfluorene with a polynuclear aromatic dibromide. The 9,10-disubstituted anthracene was obtained exclusively for A while N and P were obtained as a mixture of two isomers with predominant the 1,4-disubstituted naphthalene and 1,8-disubstituted pyrene, respectively. The polymers were soluble in common organic solvents and decomposed above 370 degrees C. Their glass transition temperature increased from 58 to 110 degrees C by increasing the number of the phenyl rings of the polynuclear aromatic moiety. Rather high-efficiency blue and blue-greenish photoluminescence (PL) of these copolymers in solution was largely decreased in their films, indicating the presence of concentration quenching in the solid state. The OLED using these polymers demonstrated green EL in the case of copolymers N and A, and red EL in the P derivative with eta(EL) = 0.26-0.31%. (c) 2007 Wiley Periodicals, Inc.. |
| 263. | Toshinori Matsushima, Chihaya Adachi, Temperature-independent electron tunneling injection in tris (8-hydroxyquinoline) aluminum thin film from high-work-function gold electrode, THIN SOLID FILMS, 10.1016/j.tsf.2008.02.012, 516, 15, 5069-5074, 2008.06, We fabricated electron-only tris (8-hydroxyquinoline) aluminum (Alq(3)) single-layer devices with a device structure of glass substrate/MgAg anode (100 nm)/Alq(3) layer (100 nm)/metal cathode (100 nm), and systematically varied the work functions (WF) of the metal cathodes from WF=-1.9 (Cs) to -2.9 (Ca), -3.8 (Mg), -4.4 (Al), -4.6 (Ag), and -5.2 eV (Au) to investigate how electron injection barriers at the cathode/Alq(3) interfaces influence their current density-voltage (J-V) characteristics. We found that current densities at a certain driving voltage decrease and the temperature dependence of J-V characteristics of the devices gradually becomes weaker as the work functions of the metal cathodes are decreased. The device with the highest-work-function Au cathode exhibited virtually temperature-independent J-V characteristics, suggesting that a current flow mechanism of this device is mainly controlled by electron tunneling injection at the Au/Alq(3) interface. (C) 2008 Elsevier B.V. All rights reserved.. |
| 264. | Daisuke Yokoyama, Masato Moriwake, Chihaya Adachi, Spectrally narrow emissions at cutoff wavelength from edges of optically and electrically pumped anisotropic organic films (vol 103, artn 123104, 2008), JOURNAL OF APPLIED PHYSICS, 10.1063/1.2976164, 104, 3, 2008.08. |
| 265. | Masayuki Yahiro, Tomo Sakanouel, Hiroyuki Uchiuzou, Takahito Oyamada, Akio Toshimitsu, Chihaya Adachi, Material design of organic semiconductors for light emitting organic field-effect transistors and their device characteristics, JOURNAL OF SYNTHETIC ORGANIC CHEMISTRY JAPAN, 10.5059/yukigoseikyokaishi.66.493, 66, 5, 493-503, 2008.05, In this study, we report on material design of light-emitting organic field effect transistors (LE-OFETs). Some of newly synthesized pyrene and bis-styryl derivatives as an active layer demonstrated high field effect mobility (mu(h) = 0.11 cm(2)/VS, C 6-BSBP) and high photoluminescence efficiency (phi(PL)similar to 80%, symmetrical di-substituted pyrene derivatives). Further, external electroluminescence quantum efficiency was improved from 0.01% in TPPy to 0.15 similar to 0.54% in pyrene dimmers. In addition, we demonstrate an increase of EL efficiency by introducing guest-host system and ambipolar operation mechanism.. |
| 266. | Naoki Matsumoto, Masakazu Nishiyarna, Chihaya Adachi, Exciplex formations between tris(8-hydoxyquinolate)aluminum and hole transport materials and their photoluminescence and electroluminescence characteristics, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp800443r, 112, 20, 7735-7741, 2008.05, We investigated exciplex formations between tris(8-hydoxyquinolate)aluminum (Alq(3)) and hole transport materials (HTMs) that have various highest occupied molecular orbital (HOMO) levels (-6.0 to -5.1 eV). The investigation focused on the photoluminescence and electroluminescence characteristics of Alq(3):HTM codeposited films. Intermolecular interaction between Alq3 and the HTMs correlated with the HOMO levels of the HTMs. In the HTMs with HOMO levels ranging between -5.3 and -5.1 eV, the exciplex formation was clearly observed. No appreciable exciplex formation was observed in the HTMs with HOMO levels between -6.0 and -5.4 eV. The HTMs with -5.5 and -5.4 eV of HOMO levels, which are in an equivocal gray zone, showed weak intermolecular interaction, leading to a slight decrease in Alq(3) fluorescence efficiency without a significant spectral shift. The quenching of Alq(3) fluorescence by such weak intermolecular interaction was signaled by an external electric field. We observed that this type of weak exciplex formation also affected the electroluminescence quantum efficiency of HTM/Alq(3)-based organic light emitting diodes (OLEDs); therefore, it is necessary to control this delicate interface interaction to maximize OLED performance.. |
| 267. | Hajime Nakanotani, Masatoshi Saito, Hiroaki Nakamura, Chihaya Adachi, Tuning of threshold voltage by interfacial carrier doping in organic single crystal ambipolar light-emitting transistors and their bright electroluminescence, APPLIED PHYSICS LETTERS, 10.1063/1.3216047, 95, 10, 2009.09, Organic light-emitting field-effect transistors, based on a p-bis[(p-styryl)styryl] benzene (P5V4) single crystal, that possess high mobilities of over 0.1 cm(2)/V s for both electrons and holes were fabricated. For a small charge injection barrier and successive formation of high exciton density in the carrier recombination zone, the hole accumulation threshold voltage was significantly reduced by interfacial hole doping based on electron transfer from P5V4 molecules to a molybdenum oxide layer. The threshold voltage for hole accumulation was drastically decreased from -80 +/- 3 to 2 +/- 3 V, leading to dual charge injection and accumulation of a very high current density of J>100 A cm(-2) with intense edge electroluminescence.. |
| 268. | Ayataka Endo, Mai Ogasawara, Atsushi Takahashi, Daisuke Yokoyama, Yoshimine Kato, Chihaya Adachi, Thermally Activated Delayed Fluorescence from Sn4+-Porphyrin Complexes and Their Application to Organic Light-Emitting Diodes - A Novel Mechanism for Electroluminescence, ADVANCED MATERIALS, 10.1002/adma.200900983, 21, 47, 4802-+, 2009.12, Electroluminescence based on TADF, that is, thermally activated delayed fluorescence, is demonstrated in Sn4+-porphyrin complexes. On excitation by a short electrical pulse, prompt and delayed electroluminescence components were clearly observed. The delayed component was composed of both TADF and phosphorescence (see figure), and the TADF component significantly increased with increasing temperature.. |
| 269. | Tung-Huei Ke, Robert Gehlhaar, Chih-Hsin Chen, Jiann-T Lin, Chung-Chih Wu, Chihaya Adachi, Single molecule color controllable light emitting organic field effect transistors for white light emission with high color stability, APPLIED PHYSICS LETTERS, 10.1063/1.3202763, 95, 6, 2009.08, The authors report on color controllable white light emission from a unipolar organic light emitting transistor. We demonstrate light emission with two distinct peaks: a spectrally narrow blue emission from monomers and a yellow broadband emission created close to the interface of the organic film and SiO(2). Due to the functionality of Mg/Au stacked electrodes, we are able to position the recombination zone via gate voltage control. Therefore, we are able to shift the spectral peak position and change the emission intensity independently by the drain voltage. The emission color is tunable from CIE coordinates (0.27, 0.28) to (0.40, 0.41).. |
| 270. | Ayataka Endo, Chihaya Adachi, Photoluminescence characteristics of tris(2-phenylquinoline)iridium(III) dispersed in an iridium complex host layer, CHEMICAL PHYSICS LETTERS, 10.1016/j.cplett.2009.10.064, 483, 4-6, 224-226, 2009.12, We studied the photoluminescence (PL) characteristics of the red phosphor tris(2-phenylquinoline)iridium(III) (Ir(phq)(3)) doped into an Ir complex host layer. Although we expect efficient triplet exciton confinement by the host Ir complexes because of their triplet energy level being higher than that of Ir(phq)(3), we observed a rather low PL quantum efficiency. We clarified that the short Forster energy transfer distance in the host layers resulted in limited energy transfer between host and guest molecules. (C) 2009 Elsevier B. V. All rights reserved.. |
| 271. | Denghui Xu, Chihaya Adachi, Organic light-emitting diode with liquid emitting layer, APPLIED PHYSICS LETTERS, 10.1063/1.3200947, 95, 5, 2009.08, We demonstrate an original organic light-emitting diode (OLED) having a neat liquid host of 9-(2-ethylhexyl)carbazole (EHCz) doped with a guest emitter of 5,6,11,12-tetraphenylnapthacene (rubrene). The device structure is composed of indium tin-oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate)/EHCz:rubrene/Cs(2)CO(3)/ITO. We demonstrate that the liquid organic semiconducting layer surely transports charge carriers, leading to electroluminescence from rubrene with the highest external quantum efficiency of eta(ext)=0.03% at a current density of 0.26 mA/cm(2). Our demonstration of the liquid-OLEDs will open another possibility of organic semiconductors and light-emitting applications.. |
| 272. | Yuki Shibano, Hiroshi Imahori, Chihaya Adachi, Organic Thin-Film Solar Cells Using Electron-Donating Perylene Tetracarboxylic Acid Derivatives, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp9045726, 113, 34, 15454-15466, 2009.08, Various electron-donating amino groups were introduced into the perylene core of perylene tetracarboxylic acid derivatives (PTCs) to address the potential use in organic solar cells. Broad absorptions of the PTC solutions in the visible to near-infrared (NIR) region suggest that PTCs are promising light-harvesting molecules for solar cells. Electrochemical measurements reveal that the introduction of the electron-donating amino groups makes the energy level of the highest occupied molecular orbital (HOMO) shallow, imparting electron-rich characteristics to the PTCs. The electronic properties of the PTCs are studied oil the basis of quantum chemical calculations. The results show that the variation of the amino groups has a significant influence oil the HOMO level, while the lowest unoccupied molecular orbital (LUMO) level is relatively sensitive to the electronegativity of the PTC terminal atoms. The PTC thin films exhibit broad absorption bands in the visible to NIR region, as for the PTC solutions, and possess relatively shallow HOMO and LUMO energies that are higher or comparable to those of fullerene C-60. These excellent properties encouraged us to employ amine-substituted PTCs as electron donors in a thin film solar cell with C-60 as an n-type semiconductor, Photovoltaic devices with 1 structure of indium tin oxide (ITO)/PTCS/C-60/bathocuproine (BCP)/Al were fabricated by spin-coating PTCs on ail ITO electrode. The devices with perylene tetracarboxylic acid diimides (PTCDIs), bearing highly basic amino groups (Py-PTCDI, Me2N-PTCDI,and Ph2N-PTCDI), exhibit the higher power conversion efficiencies than those with carbazoyl PTCDI (Cz-PTCDI) and perylene tetracarboxylic acid dianhydrides (PTCDAs). The higher device performance originates from the efficient electron transfer from the PTCs to C-60 as the results of the relatively shallow HOMO and LUMO levels of the PTCs bearing the highly basic amino groups. The dependence of the device performance on the PTC film thickness indicates that the introduction of diphenylamino groups on the perylene core suppresses the nonradiative decay of the exciton without decreasing the hole mobility. These results will provide important information for the molecular design of post PTC derivatives.. |
| 273. | Hajime Nakanotani, Masatoshi Saito, Hiroaki Nakamura, Chihaya Adachi, Highly balanced ambipolar mobilities with intense electroluminescence in field-effect transistors based on organic single crystal oligo(p-phenylenevinylene) derivatives, APPLIED PHYSICS LETTERS, 10.1063/1.3184588, 95, 3, 2009.07, Single crystal organic field-effect transistors (FETs) based on highly luminescent oligo(p-phenylenevinylene) (OPV) derivatives are fabricated. Although OPV single crystal FETs show both p- and n- type FET operation, we found that an increase in the conjugation length of the OPV derivatives from three phenylene rings (P3V2) to four phenylene rings (P4V3) results in an improvement in the electron mobility by an order of magnitude, while retaining the high hole mobility. This molecular design, using P4V3, achieved an ambipolar light-emitting OFET with well-balanced high hole (0.12 cm(2)/V s) and electron (0.11 cm(2)/V s) mobilities, leading to intense electroluminescence.. |
| 274. | Tung-Huei Ke, Robert Gehlhaar, Chih-Hsin Chen, Jiann-T Lin, Chung-Chih Wu, Chihaya Adachi, High efficiency blue light emitting unipolar transistor incorporating multifunctional electrodes, APPLIED PHYSICS LETTERS, 10.1063/1.3109800, 94, 15, 2009.04, The authors report on blue light emitting unipolar organic light emitting transistors (OLETs) with external quantum efficiency up to 0.2% by using multifunctional Mg/Au electrodes formed in combination with an efficient light emitting fluorene derivative. A mobility up to 6x10(-6) cm(2) V(-1) s(-1) has been achieved, which is comparable to previous results from time of flight mobility measurements. An anomalous light emission behavior is observed in unipolar OLETs. The phenomenon is discussed in light of the effects of electron injection and outcoupling efficiency, respectively. Our results show that the multifunctional electrodes are useful for implementing highly efficient unipolar OLETs.. |
| 275. | Daisuke Yokoyama, Akio Sakaguchi, Michio Suzuki, Chihaya Adachi, Enhancement of electron transport by horizontal molecular orientation of oxadiazole planar molecules in organic amorphous films, APPLIED PHYSICS LETTERS, 10.1063/1.3274135, 95, 24, 2009.12, To demonstrate the effect of molecular orientation on charge transport characteristics in vacuum-deposited organic amorphous films, the electrical and optical properties of films of two oxadiazole derivatives were investigated. One of them has bulky tert-butyl terminals and forms an isotropic film, whereas the other has planar bipyridyl terminals and forms a highly anisotropic film. The very large optical anisotropy of the latter means that the planar molecules stack horizontally, leading to large overlaps of pi-orbitals and more than 30 times higher electron mobility though the geometric and electronic structures of the main conformers of the two derivatives are quite similar.. |
| 276. | Naoki Matsumoto, Takanori Miyazaki, Masakazu Nishiyama, Chihaya Adachi, Efficient Deep-Blue Organic Light-Emitting Diodes Based on 9,9-Bis(4-biphenylyl)fluorene Derivatives, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp809024h, 113, 15, 6261-6266, 2009.04, We fabricated highly efficient deep-blue organic light-emitting diodes (OLEDs) composed of 2,7-bis(4'-diphenylamino-1,1'-biphenyl-4-yl)-9,9-bis(1,1'-biphenyl-4-yl)-9H-fluorene (FLBD) as an emitter doped into a wider energy gap host of 2,7-bis(1,1'-biphenyl-4-yl)-9,9-bis(1,1'-biphenyl-4-yl)-9H-fluorene (FLBH). We investigated the dominant factors for external electroluminescence quantum efficiency (eta(ext)) in the deep-blue OLEDs by focusing on the carrier balance in the en-fitting layer (EML), the location and width of the carrier recombination zone, and carrier-induced exciton quenching. The eta(ext) value of the OLEDs strongly depended on the hole injection efficiency from a hole transport layer (HTL) to the EML. By controlling the hole injection barrier into the EML and balancing the number of electrons and holes in the EML using HTLs having various highest occupied molecular orbital levels, we obtained the highest eta(ext) of 5.4% with deep-blue Commission International De L'Eclairage coordinates of x = 0. 15 and y = 0.09. Additionally, we found that the width of the carrier recombination zone tightly correlates to the hole injection efficiency into the EML.. |
| 277. | Ryota Kabe, Hajime Nakanotani, Tomo Sakanoue, Masayuki Yahiro, Chihaya Adachi, Effect of Molecular Morphology on Amplified Spontaneous Emission of Bis-Styrylbenzene Derivatives, ADVANCED MATERIALS, 10.1002/adma.200803588, 21, 40, 4034-+, 2009.10, Molecular aggregation greatly affects the fluorescence quantum efficiency, transient lifetime, and amplified spontaneous emission (ASE) of bis-styrylbenzene derivatives. We compare the optical properties for various morphologies (solution, film, doped film, and single crystalline state) (see figure) and demonstrate that ambi-polar operation of a 1,4-bis(4-methylstyryl) benzene layer in field-effect transistors leads to intense blue electroluminescence with a rather sharp emission width.. |
| 278. | Tomo Sakanoue, Toru Irie, Chihaya Adachi, Charge separation and transport behavior of a two-dimensional charge sheet at organic donor-acceptor heterointerfaces, JOURNAL OF APPLIED PHYSICS, 10.1063/1.3137192, 105, 11, 2009.06, Charge separation and transport behavior were investigated at an organic heterolayered interface consisting of a 4,4', 4 ''- tris[3-methylphenyl(phenyl)amino] triphenylamine (m-MTDATA) organic donor and a hexadecafluoro-copper-phthalocyanine (F(16)CuPc) organic acceptor. A two-dimensional charge sheet of electron-hole pairs was induced due to the formation of charge-transfer complexes at the heterointerface. The induced charges could be separated by application of an electric field perpendicular to the heterointerface. The charge-separation behavior was independent of the work function of the contact electrodes but was strongly dependent on the energy-level alignment between the highest occupied molecular orbital of the donor molecules and the lowest unoccupied molecular orbital of the acceptor molecules. This enabled the preparation of an organic light-emitting diode without injecting holes from the anode. The charge-transport behavior along the heterointerface was also investigated by fabricating laterally arranged contact electrodes. The F(16)CuPc/m-MTDATA heterointerface exhibited high conductivity of 0.001 S/cm, which is seven orders of magnitude higher than that of a single-layer F(16)CuPc or m-MTDATA film. In situ electrical measurements during formation of the heterointerface enabled the effective thickness of the charge sheet to be determined as being accumulated within 2-3 nm, which corresponds to the bilayer of both F(16)CuPc and m-MTDATA. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3137192]. |
| 279. | Kenji Kawano, Chihaya Adachi, Reduced initial degradation of bulk heterojunction organic solar cells by incorporation of stacked fullerene and lithium fluoride interlayers, APPLIED PHYSICS LETTERS, 10.1063/1.3297876, 96, 5, 2010.02, Reduced initial degradation of bulk heterojunction organic solar cells (OSCs) was achieved by inclusion of stacked fullerene (C(60)) and lithium fluoride interlayers. By inserting a 3 nm C(60) layer and a 0.5 nm LiF layer between the photoactive layer and Al cathode in an OSC, the device lifetime calculated after an initial 8 h continuous illumination period was dramatically improved, with a decrease of only 5% in the power conversion efficiency. The 3 nm C(60) layer forms a unique surface pattern of microscopic domes, and the combination of this layer with a 0.5 nm LiF layer formed an Ohmic-like contact between the photoactive layer and the Al cathode, resulting in a significant reduction in the degradation of the OSC.. |
| 280. | Ayataka Endo, Chihaya Adachi, Photoluminescence Characteristics of Organic Host Materials with Wide Energy Gaps for Organic Electrophosphorescent Devices, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.1143/JJAP.49.050205, 49, 5, 2010.05, The photoluminescence, i.e., fluorescence and phosphorescence, characteristics of host materials with wide energy gaps suitable for phosphorescence-based organic light-emitting diodes (OLEDs) are summarized. In the vacuum deposited films, the host materials show phosphorescent emission in the blue to green region and triplet energy levels of E(T) = 2.6-3.1 eV because of the presence of steric hindrance. An OLED containing 1,2,3,4-tetraphenyl-5-(3-pyridyl)benzene as a host and iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,C(2)]picolinate as a blue emissive phosphorescent dopant exhibits an external electroluminescence efficiency of similar to 12%. (C) 2010 The Japan Society of Applied Physics. |
| 281. | Daisuke Yokoyama, Yousuke Setoguchi, Akio Sakaguchi, Michio Suzuki, Chihaya Adachi, Orientation Control of Linear-Shaped Molecules in Vacuum-Deposited Organic Amorphous Films and Its Effect on Carrier Mobilities, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.200901684, 20, 3, 386-391, 2010.02, The molecular orientation of linear-shaped molecules in organic amorphous films is demonstrated to be controllable by the substrate temperature. It is also shown that the molecular orientation affects the charge-transport characteristics of the films. Although linear-shaped 4,4'-bis[{N-carbazole}styryl]biphenyl molecules deposited on substrates at room temperature are horizontally oriented in amorphous films, their orientation when deposited on heated substrates with smooth surfaces becomes more random as the substrate temperature increases, even at temperatures under the glass transition temperature. Another factor dominating the orientation of the molecules deposited on heated substrates is the surface roughness of the substrate. Lower carrier mobilities are observed in films composed of randomly oriented molecules, demonstrating the significant effect of a horizontal molecular orientation on the charge-transport characteristic of organic amorphous films.. |
| 282. | Zhonglian Wu, Benhu Fan, Feng Xue, Chihaya Adachi, Jianyong Ouyang, Organic molecules based on dithienyl-2,1,3-benzothiadiazole as new donor materials for solution-processed organic photovoltaic cells, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 10.1016/j.solmat.2010.07.017, 94, 12, 2230-2237, 2010.12, Polymers based on dithienyl-2,1,3-benzothiadiazole (TBT) have received strong attention as the donor materials of polymer photovoltaic cells (PVs), since they can have a low band gap. But soluble small organic molecules based on TBT have been rarely studied. This paper reports the synthesis of two small organic molecules based on TBT and their application as the donor materials of solution-processed bulk heterojunction organic photovoltaic cells (OPVs). These compounds were soluble in common organic solvents, such as chloroform, chlorobenzene and tetrahydrofuran. They have band gaps comparable to poly(3-hexylthiophene) (P3HT) and lower HOMO and LUMO (HOMO: highest occupied molecular orbital. LUMO: lowest unoccupied molecular orbital) levels than P3HT. These molecules and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were used as the donors and acceptor to fabricate bulk heterojunction OPVs through solution processing. After optimization of the experimental conditions, power conversion efficiency (PCE) of 0.66% was achieved on the solution-processed OPVs under AM 1.5G, 100 mW cm(-2) illumination. (C) 2010 Elsevier B.V. All rights reserved.. |
| 283. | Hajime Nakanotani, Chihaya Adachi, Organic light-emitting diodes containing multilayers of organic single crystals, APPLIED PHYSICS LETTERS, 10.1063/1.3298558, 96, 5, 2010.02, Double-heterostructure (DH) organic light-emitting diodes (OLEDs) with thick carrier transport layers based on organic single crystals have been fabricated. Although the total thickness of the organic layers (similar to 1.4 mu m) is one order of magnitude greater than that of conventional thin-film OLEDs, a current density of 100 mA/cm(2) was achieved at 19 V. The major advantage of the single crystal-based DH-OLED was that a very low applied electric field (similar to 10(4) V/cm) was required for the onset of carrier injection and transport, because of the high carrier mobilities of the single crystal layers.. |
| 284. | Daisuke Yokoyama, Chihaya Adachi, In situ real-time spectroscopic ellipsometry measurement for the investigation of molecular orientation in organic amorphous multilayer structures, JOURNAL OF APPLIED PHYSICS, 10.1063/1.3432568, 107, 12, 2010.06, To investigate molecular orientation in organic amorphous films, in situ real-time spectroscopic ellipsometry measurements were performed during vacuum deposition. Three materials with different molecular shapes were adopted to confirm the generality of the molecular orientation. In all three cases, more than 200 000 values for the ellipsometric parameters measured during deposition were well simulated simultaneously over the entire spectral range and measurement period using a simple model where the films possessed homogeneous optical anisotropy. This demonstrated the homogeneity of the molecular orientation in the direction of film thickness. The molecular orientation can be controlled by the substrate temperature even in multilayer structures. It is also demonstrated that a "multilayer structure" can be fabricated using only one material, where each layer has different optical and electrical properties. (C) 2010 American Institute of Physics. [doi:10.1063/1.3432568]. |
| 285. | Naoki Matsumoto, Chihaya Adachi, Exciplex Formations at the HTL/Alq(3) Interface in an Organic Light-Emitting Diode: Influence of the Electron-Hole Recombination Zone and Electric Field, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp9121062, 114, 10, 4652-4658, 2010.03, In this work, we investigate the influence of weak intermolecular interactions, which have not previously been carefully considered, in hole transport material (HTM)/tris(8-hydroxyquinoline)aluminum) (Alq(3))-based organic light-emitting diodes (OLEDs). Although such weak interactions quench Alq(3) fluorescence, no significant spectral shift is identified. Electroluminescence of OLEDs containing HTM-Alq(3) codeposited (mixed) emitter is quenched by the Formation of such exciplexes. In general, the electroluminescence quantum efficiency of OLEDs correlates closely with the photoluminescence quantum yields of HTM:Alq(3) codeposited films. In contrast, in all OLED containing a layered structure of HTM/Alq(3), exciplexes ire less effective at quenching the electroluminescence of AIq(3). Because exciplexes form only at the interface between the HTM and AIq3 layers in HTM/Alq(3)-based OLEDs, exciplex formation is affected not only by the electron donating nature of the HTM but also by the position of the electron-hole recombination zone and the application of an external electric field during OLED operation.. |
| 286. | Hajime Nakanotani, Masatoshi Saito, Hiroaki Nakamura, Chihaya Adachi, Emission Color Tuning in Ambipolar Organic Single-Crystal Field-Effect Transistors by Dye-Doping, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.200902339, 20, 10, 1610-1615, 2010.05, The effect of dye-doping in ambipolar light-emitting organic field-effect transistors (LE-OFETs) is investigated from the standpoint of the carrier mobilities and the electroluminescence (EL) characteristics under ambipolar operation. Dye doping of organic crystals permits not only tuning of the emission color but also significantly increases the efficiency of ambipolar LE-OFETs. A rather high external EL quantum efficiency (similar to 0.64%) of one order of magnitude higher than that of a pure p-distyrylbenzene (P3V2) single crystal is obtained by tetracene doping. The doping of tetracene molecules into a host P3V2 crystal has almost no effect on the electron mobility and the dominant carrier recombination process in the tetracene-doped P3V2 crystal involves direct carrier recombination on the tetracene molecules.. |
| 287. | Joerg Frischeisen, Daisuke Yokoyama, Chihaya Adachi, Wolfgang Bruetting, Determination of molecular dipole orientation in doped fluorescent organic thin films by photoluminescence measurements, APPLIED PHYSICS LETTERS, 10.1063/1.3309705, 96, 7, 2010.02, The orientation of the transition dipole moments of fluorescent organic molecules doped into a matrix material is determined by photoluminescence measurements of the angular dependent emission spectra and by comparison with simulations. The analysis of two small molecular materials doped into a 4,4(')-bis(N-carbazole)-biphenyl matrix is demonstrated, yielding a horizontal orientation of 91% for 4,4(')-bis[4-(diphenylamino)styryl]biphenyl and a completely random orientation in case of tris-(8-hydroxyquinoline)aluminum (Alq(3)). This expeditious technique does not require detailed information about the optical properties of the dopant, making this method particularly suitable for characterizing newly developed materials for organic light-emitting diodes with enhanced light-outcoupling efficiency.. |
| 288. | Ohkita Masakazu, Endo Ayataka, Sumiya Kimihiro, Nakanotani Hajime, Suzuki Takanori, Adachi Chihaya, Photophysical characteristics of 4,4’-bis(N-carbazolyl)tolan derivatives and their application in organic light emitting diodes, Journal of Luminescence, 10.1016/j.jlumin.2011.01.028, 131, 7, 1520-1524, 2011.07. |
| 289. | Joerg Frischeisen, Quan Niu, Alaa Abdellah, Joerg B. Kinzel, Robert Gehlhaar, Giuseppe Scarpa, Chihaya Adachi, Paolo Lugli, Wolfgang Bruetting, Light extraction from surface plasmons and waveguide modes in an organic light-emitting layer by nanoimprinted gratings, OPTICS EXPRESS, 19, 1, A7-A19, 2011.01, Organic light-emitting diodes (OLEDs) usually exhibit a low light outcoupling efficiency because a large fraction of power is lost to surface plasmons (SPs) and waveguide modes. In this paper it is demonstrated that periodic grating structures with almost mu m-scale can be used to extract SPs as well as waveguide modes and therefore enhance the outcoupling efficiency in light-emitting thin film structures. The gratings are fabricated by nanoimprint lithography using a commercially available diffraction grating as a mold which is pressed into a polymer resist. The outcoupling of SPs and waveguide modes is detected in fluorescent organic films adjacent to a thin metal layer in angular dependent photoluminescence measurements. Scattering up to 5th-order is observed and the extracted modes are identified by comparison to the SP and waveguide dispersion obtained from optical simulations. In order to demonstrate the low-cost, high quality and large area applicability of grating structures in optoelectronic devices, we also present SP extraction using a grating structure fabricated by a common DVD stamp. (C)2010 Optical Society of America. |
| 290. | Joerg Frischeisen, Quan Niu, Alaa Abdellah, Joerg B. Kinzel, Robert Gehlhaar, Giuseppe Scarpa, Chihaya Adachi, Paolo Lugli, Wolfgang Bruetting, Light extraction from surface plasmons and waveguide modes in an organic light-emitting layer by nanoimprinted gratings, OPTICS EXPRESS, 10.1364/OE.19.0000A7, 19, 1, A7-A19, 2011.01, Organic light-emitting diodes (OLEDs) usually exhibit a low light outcoupling efficiency because a large fraction of power is lost to surface plasmons (SPs) and waveguide modes. In this paper it is demonstrated that periodic grating structures with almost mu m-scale can be used to extract SPs as well as waveguide modes and therefore enhance the outcoupling efficiency in light-emitting thin film structures. The gratings are fabricated by nanoimprint lithography using a commercially available diffraction grating as a mold which is pressed into a polymer resist. The outcoupling of SPs and waveguide modes is detected in fluorescent organic films adjacent to a thin metal layer in angular dependent photoluminescence measurements. Scattering up to 5th-order is observed and the extracted modes are identified by comparison to the SP and waveguide dispersion obtained from optical simulations. In order to demonstrate the low-cost, high quality and large area applicability of grating structures in optoelectronic devices, we also present SP extraction using a grating structure fabricated by a common DVD stamp. (C)2010 Optical Society of America. |
| 291. | Hirotaka So, Hirofumi Watanabe, Masayuki Yahiro, Yu Yang, Yuji Oki, Chihaya Adachi, Highly photostable distributed-feedback polymer waveguide blue laser using spirobifluorene derivatives, OPTICAL MATERIALS, 10.1016/j.optmat.2010.12.011, 33, 6, 755-758, 2011.04, In this study, we synthesized the new spirobifluorene derivatives; hexylbiphenyl-spirobifluorene (HBP-Spiro) and triphenylamine-spirobifluorene (TPA-Spiro) and demonstrated the operation of a distributed-feedback polymer waveguide blue laser. In addition, we investigated the optical and lasing properties of spirobifluorene derivatives including photostability. The experimental slope efficiency and the energy threshold of a HBP-Spiro-doped waveguide laser were 3.6% and 1.9 mu J, respectively. An operation lifetime of 27,000 shots was obtained for a pump-pulse duration of 1.2 ns and energy of 3.0 mu J at a wavelength of 355 nm. (C) 2011 Elsevier B.V. All rights reserved.. |
| 292. | Takuji Kato, Mao Yasumatsu, Chikako Origuchi, Kyoji Tsutsui, Yasukiyo Ueda, Chihaya Adachi, High Carrier Mobility of 3.8 cm(2) V-1 s(-1) in Polydiacetylene Thin Films Polymerized by Electron Beam Irradiation, APPLIED PHYSICS EXPRESS, 10.1143/APEX.4.091601, 4, 9, 2011.09, The highest carrier mobility of polydiacetylene (PDA) thin films in field-effect transistors has been limited to less than 0.8cm(2) V-1 s(-1), although the main chain conduction should show higher carrier mobility potentially. We revealed that the cause of the low carrier mobility is due to the presence of local upheaval regions generated by the volume change through the polymerization process of diacetylene monomers. In order to suppress the occurrence of the upheaval regions, we found that electron beam (EB) irradiation is effective, resulted in the highest carrier mobility of mu(max) = 3.8 cm(2) V-1 s(-1). (C) 2011 The Japan Society of Applied Physics. |
| 293. | Ye Zou, Zhenbo Deng, William J. Potscavage, Masaya Hirade, Yanqiong Zheng, Chihaya Adachi, Very high open-circuit voltage of 5.89 V in organic solar cells with 10-fold-tandem structure, APPLIED PHYSICS LETTERS, 10.1063/1.4729009, 100, 24, 2012.06, Organic solar cells (OSCs) based on chloroaluminum phthalocyanine (ClAlPc) as donor and fullerene C-60 as acceptor with a multi-tandem structure were fabricated. We demonstrated very high open-circuit voltage (V-OC) and enhanced power conversion efficiency (PCE) for the multi-tandem OSCs. Using a fivefold structure, we obtained PCE of 2.49% with a V-OC of 3.50 V, in comparison with PCE of similar to 2% and V-OC of 0.72-0.81V for the single device. We also fabricated a tenfold-stacked OSC showing an extremely high V-OC of 5.89 V. The multi-tandem OSCs with very high V-OC have great potential for applications in limited-area low-power electronics. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729009]. |
| 294. | Hitoshi Yamamoto, Chihaya Adachi, Michael S. Weaver, Julie J. Brown, Identification of device degradation positions in multi-layered phosphorescent organic light emitting devices using water probes, APPLIED PHYSICS LETTERS, 10.1063/1.4711129, 100, 18, 2012.04, We exposed regions of green phosphorescent organic light emitting devices (PHOLED(TM)s) consisting of a fac-tris(2-phenylpyridine)iridium (Ir(ppy)(3)) as the phosphorescent emitter to a partial pressure of water of 3 x 10(-4) Pa during device fabrication to induce degradation in a specific region of the multi-layered devices. We identified the interface between the hole transport layer and the emissive layer as the most susceptive region to degradation. We discuss the luminance loss mechanism and estimate an operational lifetime of 10 000 h, after 20% loss of the initial luminance from 1000 cd/m(2), is attainable from an Ir(ppy)(3) PHOLED fabricated under ultra-high vacuum conditions. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4711129]. |
| 295. | 平田修造, 安達千波矢, 渡辺敏行, 戸谷健朗, 常温大気中で高効率蓄光機能を示す有機材料, KOBUNSHI RONBUNSHU, 10.1295/koron.70.623, 70, 11, 623-636, 2013.10. |
| 296. | Yoshiyuki Nonoguchi, Kenji Ohashi, Rui Kanazawa, Koji Ashiba, Kenji Hata, Tetsuya Nakagawa, Chihaya Adachi, Tomoaki Tanase, Tsuyoshi Kawai, Systematic Conversion of Single Walled Carbon Nanotubes into n-type Thermoelectric Materials by Molecular Dopants, SCIENTIFIC REPORTS, 10.1038/srep03344(2013), 3, 3344, 3344, 2013.11, Thermoelectrics is a challenging issue for modern and future energy conversion and recovery technology. Carbon nanotubes are promising active thermoelectic materials owing to their narrow bandgap energy and high charge carrier mobility, and they can be integrated into flexible thermoelectrics that can recover any waste heat. We here report air-stable n-type single walled carbon nanotubes with a variety of weak electron donors in the range of HOMO level between ca. -4.4 eV and ca. -5.6 eV, in which partial uphill electron injection from the dopant to the conduction band of single walled carbon nanotubes is dominant. We display flexible films of the doped single walled carbon nanotubes possessing significantly large thermoelectric effect, which is applicable to flexible ambient thermoelectric. |
| 297. | Shuzo Hirata, Kenro Totani, Hironori Kaji, Martin Vacha, Toshiyuki Watanabe, Chihaya Adachi, Reversible Thermal Recording Media Using Time-Dependent Persistent Room Temperature Phosphorescence, ADVANCED OPTICAL MATERIALS, 10.1002/adom.201300136, 1, 6, 438-442, 2013.06. |
| 298. | Hajime Nakanotani, Chihaya Adachi, Light-Emitting Organic Crystal Field-Effect Transistors for Future Organic Injection Lasers, Physics of Organic Semiconductors: Second Edition, 10.1002/9783527655946.ch18, 603-621, 2013.01. |
| 299. | Hajime Nakanotani, Chihaya Adachi, Amplified Spontaneous Emission and Electroluminescence from Thiophene/Phenylene Co-Oligomer-Doped p-bis(p-Styrylstyryl)Benzene Crystals, ADVANCED OPTICAL MATERIALS, 10.1002/adom.201200066, 1, 6, 422-427, 2013.06. |
| 300. | Hitoshi Yamamoto, Michael S. Weaver, Hideyuki Murata, Chihaya Adachi, Julie J. Brown, Understanding extrinsic degradation in phosphorescent OLEDs, Digest of Technical Papers - SID International Symposium, 10.1002/j.2168-0159.2014.tb00199.x, 45, 1, 758-761, 2014.01, We quantified water as an impurity in OLEDs and investigated how the water level impacts initial lifetime decay. We also demonstrated a two to three fold increase in lifetime for blue and green phosphorescent OLEDs by reducing the amount of water in the devices. © 2014 Society for Information Display.. |
| 301. | Jie Li, Qisheng Zhang, Hiroko Nomura, Hiroshi Miyazaki, Chihaya Adachi, Thermally activated delayed fluorescence from (3)n pi* to (1)n pi* up-conversion and its application to organic light-emitting diodes, APPLIED PHYSICS LETTERS, 10.1063/1.4887346, 105, 1, 2014.07, Intense n pi* fluorescence from a nitrogen-rich heterocyclic compound, 2,5,8-tris(4-fluoro-3-methylphenyl)-1,3,4,6,7,9,9b-heptaazaphenalene (HAP-3MF), is demonstrated. The overlap-forbidden nature of the np* transition and the higher energy of the (3)pi pi* state than the 3 n pi* one lead to a small energy difference between the lowest singlet (S-1) and triplet (T-1) excited states of HAP-3MF. Green-emitting HAP-3MF has a moderate photoluminescence quantum yield of 0.26 in both toluene and doped film. However, an organic light-emitting diode containing HAP-3MF achieved a high external quantum efficiency of 6.0%, indicating that HAP-3MF harvests singlet excitons through a thermally activated T-1 -> S-1 pathway in the electroluminescent process. (C) 2014 AIP Publishing LLC.. |
| 302. | Hajime Nakanotani, Kensuke Masui, Junichi Nishide, Takumi Shibata, Chihaya Adachi, Promising operational stability of high-efficiency organic light-emitting diodes based on thermally activated delayed fluorescence (vol 3, 2127, 2013), SCIENTIFIC REPORTS, 10.1038/srep03640, 4, 2014.01. |
| 303. | Hiroshi Fujimoto, Takuya Miyayama, Noriaki Sanada, Chihaya Adachi, Origin of external quantum efficiency degradation in organic light-emitting diodes with a DC magnetron sputtered cathode, Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics, 10.1116/1.4897920, 32, 6, 2014.11, This paper characterizes changes in organic light-emitting diodes to better understand the origin of the decrease in external quantum efficiency (η< inf> ext< /inf> ) when switching the cathode deposition method from evaporation to DC magnetron sputtering. An increase of driving voltage and a hole-barrier-dependent decrease of η< inf> ext< /inf> when the Al cathode is sputtered suggest that disruption of carrier balance and penetration of holes from the emissive layer (EML) into the electron transport layer (ETL) are significant sources of the device degradation. When the ETL was doped with Li, degradation was suppressed and the increase in driving voltage was drastically reduced although η< inf> ext< /inf> still decreased by 5%-7%. Analysis of the films by time-of-flight secondary ion mass spectrometry indicates that Li diffuses into the EML when Al is sputtered, and Li is shown to act as an exciton quencher that can decrease η< inf> ext< /inf> . Doping of the ETL is also used to significantly suppress the performance reduction with sputtered cathodes even when using a phosphorescent emitter having high η< inf> ext< /inf> .. |
| 304. | Sae Youn Lee, Takuma Yasuda, Yu Seok Yang, Qisheng Zhang, Chihaya Adachi, Luminous Butterflies: Efficient Exciton Harvesting by Benzophenone Derivatives for Full-Color Delayed Fluorescence OLEDs, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.201402992, 53, 25, 6402-6406, 2014.06, Butterfly-shaped luminescent benzophenone derivatives with small energy gaps between their singlet and triplet excited states are used to achieve efficient full-color delayed fluorescence. Organic light-emitting diodes (OLEDs) with these benzophenone derivatives doped in the emissive layer can generate electroluminescence ranging from blue to orange-red and white, with maximum external quantum efficiencies of up to 14.3%. Triplet excitons are efficiently harvested through delayed fluorescence channels.. |
| 305. | Kunihisa Kato, Yoshika Hatasako, Makoto Kashiwagi, Harutoshi Hagino, Chihaya Adachi, Koji Miyazaki, Fabrication of a Flexible Bismuth Telluride Power Generation Module Using Microporous Polyimide Films as Substrates, JOURNAL OF ELECTRONIC MATERIALS, 10.1007/s11664-013-2852-0, 43, 6, 1733-1739, 2014.06, In this study, we investigated the effect of the structure of microporous p-type (Bi0.4Te3Sb1.6) and n-type (Bi2.0Te2.7Se0.3) BiTe-based thin films on their thermoelectric performance. High-aspect-ratio porous thin films with pore depth greater than 1 mu m and pore diameter ranging from 300 nm to 500 nm were prepared by oxygen plasma etching of polyimide (PI) layers capped with a heat-resistant block copolymer, which acted as the template. The cross-plane thermal conductivities of the porous p- and n-type thin films were 0.4 W m(-1) K-1 and 0.42 W m(-1) K-1, respectively, and the dimensionless figures of merit, ZT, of the p- and n-type BiTe films were estimated as 1.0 and 1.0, respectively, at room temperature. A prototype thermoelectric module consisting of 20 pairs of p- and n-type strips over an area of 3 cm x 5 cm was fabricated on the porous PI substrate. This module produced an output power of 0.1 mW and an output voltage of 0.6 V for a temperature difference of 130A degrees C. The output power of the submicrostructured module was 1.5 times greater than that of a module based on smooth BiTe-based thin films. Thus, the thermoelectric performance of the thin films was improved owing to their submicroscale structure.. |
| 306. | Ryoichi Ishimatsu, Shigeyuki Matsunami, Takashi Kasahara, Jun Mizuno, Tomohiko Edura, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Electrogenerated Chemiluminescence of Donor-Acceptor Molecules with Thermally Activated Delayed Fluorescence, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.201402615, 53, 27, 6993-6996, 2014.07, The electrochemistry and electrogenerated chemiluminescence (ECL) of four kinds of electron donor-acceptor molecules exhibiting thermally activated delayed fluorescence (TADF) is presented. TADF molecules can harvest light energy from the lowest triplet state by spin up-conversion to the lowest singlet state because of small energy gap between these states. Intense green to red ECL is emitted from the TADF molecules by applying a square-wave voltage. Remarkably, it is shown that the efficiency of ECL from one of the TADF molecule could reach about 50%, which is comparable to its photoluminescence quantum yield.. |
| 307. | Hiroshi Fujimoto, Tomohiko Edura, Takuya Miyayama, Noriaki Sanada, Chihaya Adachi, Accurate measurement of dopant concentration in organic light-emitting diodes by combining high-performance liquid chromatography and TOF-SIMS, Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, 10.1116/1.4871756, 32, 3, 2014.05, The authors report the use of high-performance liquid chromatography (HPLC) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) utilizing a gas cluster ion beam to accurately measure the dopant concentration and its depth profile in organic thin films used for organic light-emitting diodes. The total dopant concentrations estimated by HPLC for films of 4,4'-bis(carbazol-9-yl)biphenyl (CBP) doped with tris(2-phenylpyridinato)iridium(III) (Ir(ppy)3) are consistent with those measured by quartz crystal microbalances (QCMs) during the deposition. Concentrations measured for Ir(ppy)3:CBP films by HPLC and TOF-SIMS show a nearly linear relationship in the range of 1-8 wt. %. At concentrations higher than 8 wt. %, TOF-SIMS values significantly deviate because of the matrix effect. The depth profile of the dopant concentration measured by TOF-SIMS was in good agreement with that measured by QCMs during film deposition for concentrations below 8 wt. %. These methods are especially useful for comparing the dopant concentration of films deposited in different batches and equipment.. |
| 308. | Suzuki K, Kubo S, Shizu K, Fukushima T, Wakamiya A, Murata Y, Adachi C, Kaji H, Triarylboron-Based Fluorescent Organic Light-Emitting Diodes with External Quantum Efficiencies Exceeding 20 ., Angewandte Chemie (International ed. in English), 10.1002/anie.201508270, 54, 50, 15231-15235, 2015.12. |
| 309. | Rong Liu, Ryoichi Ishimatsu, Masayuki Yahiro, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Photometric flow injection determination of phosphate on a PDMS microchip using an optical detection system assembled with an organic light emitting diode and an organic photodiode, TALANTA, 10.1016/j.talanta.2014.08.057, 132, 96-105, 2015.01, A compact photometric detector was constructed from an organic light emitting diode (OLED) based on a europium complex, europium(diben-zoylmethanato)(3)(bathophenanthroline) (Eu(DBM)(3)bath), as the light source and an organic photodiode (OPD) fabricated from a hetero-junction of two layers of copper phthalocyanine (CuPc)/fullerene (C-60) as the photo-detector on a microchip prepared from poly (dimethylsiloxan) (PDMS) and was applied to the determination of phosphate. The OLED and the OPD were fabricated by a vapor deposition method on an indium tin oxide (ITO) coated glass substrate with the following layered structure; Glass (0.7 mm)/ITO (110 nm)/4,4'-bis[N-(1-naphthyl)-N-phenyl amino]biphenyl (alpha-NPD) (30 nm)/4,4'-di(N-carbazolyl)biphenyl (CBP): Eu3+ (8 wt%, 30 nm)/bathocuproine (BCP) (30 nm)/aluminum tris(8-hydroxyquinoline) (Alq(3)) (25 nm)/magnesium and silver (MgAg) (100 nm)/Ag (10 nm) and Glass (0.7 mm)/ITO (110 nm)/CuPc (35 nm)/C-60 (50 nm)/BCP (10 nm)/Ag (50 nm), respectively. The OLED based on the europium complex emitted a sharp light at the wavelength of 612 nm with a full width at half maximum (FWHM) of 8 nm. The performance of the photometric detector assembled was evaluated based on measurements of the absorbance of different concentrations of malachite green (MG) solutions for a batch system with 1 cm long path length. The molar absorptive coefficient of the MG solution, calculated from the photocurrent of the OPD, was in good agreement with the value reported in the literature. A microchip with two inlets and one outlet U-shaped channel was prepared by a conventional photolithograph method. The OLED and the OPD were configured so as to face each other through the PDMS microchip in parallel in order to align the light axis of the OLED and the OPD with the flow cell (optical path length of 5 mm), which was located at the end of outlet. For the determination of phosphate, an ion-association reaction between MG and a molybdenum-phosphate complex was utilized and a good linear relationship between the concentration and absorbance was observed in the concentration range 0-0.2 ppm, with a detection limit (S/N=3) of 0.02 ppm. The assembled photometric detector was also applied to the determination of phosphate by the flow injection of river water samples using the reagent solution containing MG and molybdenum ammonium in sulfuric acid. A good recovery (97-99%) for the river water samples, which had been spiked with the standard 0.08 ppm, with an RSD of ca 5% (n=5) was obtained using the constructed system. (C) 2014 Elsevier B.V. All rights reserved.. |
| 310. | Chihaya Adachi, Saeyoun Lee, Tetsuya Nakagawa, Katsuyuki Shizu, Kenichi Goushi, Takuma Yasuda, William J. Potscavage, Organic light-emitting diodes (OLEDs): Materials, photophysics, and device physics, Organic Electronics Materials and Devices, 10.1007/978-4-431-55654-1_2, 43-73, 2015.09, Currently, organic light-emitting diodes (OLEDs) have reached the stage of commercialization, and there has been an intense drive to use them in various applications from small-and medium-sized mobile devices to illumination equipment and large television screens. In particular, room-temperature phosphorescent materials have become core OLED components as alternatives to conventionally used fluorescent materials because devices made with phosphorescent materials exhibit excellent light-emitting performance with internal electroluminescence efficiencies (ηint) of nearly 100 %. However, phosphorescent materials have several intrinsic problems, such as being limited to metal-organic compounds containing rare metals, for example, Ir, Pt, Au, and Os, and difficulty in realizing stable blue light emission. As a result, researchers have attempted to develop new materials for use as emissive dopants in OLEDs that overcome these limitations. In this chapter, first we briefly review the progress of OLED materials and device architectures mainly based on fluorescent (first-generation) and phosphorescent (secondgeneration) emitters. Then, we discuss third-generation OLEDs that use a new light-emitting mechanism called thermally activated delayed fluorescence (TADF). Recently, highly efficient TADF, which had been difficult to realize with conventional molecular design, has been achieved by very sophisticated molecular structures, allowing access to the unlimited freedom of molecular design using carbon-based materials. This has led to the production of ultimate OLEDs that are made of common organic compounds without precious metals and can convert electricity to light at ηint of nearly 100 %.. |
| 311. | Yoshimasa Wada, Katsuyuki Shizu, Shosei Kubo, Katsuaki Suzuki, Hiroyuki Tanaka, Chihaya Adachi, Hironori Kaji, Highly efficient electroluminescence from a solution-processable thermally activated delayed fluorescence emitter, APPLIED PHYSICS LETTERS, 10.1063/1.4935237, 107, 18, 2015.11, We developed a thermally activated delayed fluorescence (TADF) emitter, 2,4,6-tris(4-(9,9-dimethylacridan-10-yl)phenyl)-1,3,5-triazine (3ACR-TRZ), suitable for use in solution-processed organic light-emitting diodes (OLEDs). When doped into 4,4'-bis(carbazol-9-yl) biphenyl (CBP) host at 16 wt. %, 3ACR-TRZ showed a high photoluminescence quantum yield of 98%. Transient photoluminescence decay measurements of the 16 wt. % 3ACR-TRZ: CBP film confirmed that 3ACR-TRZ exhibits efficient TADF with a triplet-to-light conversion efficiency of 96%. This high conversion efficiency makes 3ACR-TRZ attractive as an emitting dopant in OLEDs. Using 3ACR-TRZ as an emitter, we fabricated a solution-processed OLED exhibiting a maximum external quantum efficiency of 18.6%. (C) 2015 AIP Publishing LLC.. |
| 312. | Shuzo Hirata, Yumi Sakai, Kensuke Masui, Hiroyuki Tanaka, Sae Youn Lee, Hiroko Nomura, Nozomi Nakamura, Mao Yasumatsu, Hajime Nakanotani, Qisheng Zhang, Katsuyuki Shizu, Hiroshi Miyazaki, Chihaya Adachi, Highly efficient blue electroluminescence based on thermally activated delayed fluorescence, NATURE MATERIALS, 10.1038/NMAT4154, 14, 3, 330-336, 2015.03, Organic compounds that exhibit highly efficient, stable blue emission are required to realize inexpensive organic light-emitting diodes for future displays and lighting applications. Here, we define the design rules for increasing the electroluminescence efficiency of blue-emitting organic molecules that exhibit thermally activated delayed fluorescence. We show that a large delocalization of the highest occupied molecular orbital and lowest unoccupied molecular orbital in these charge-transfer compounds enhances the rate of radiative decay considerably by inducing a large oscillator strength even when there is a small overlap between the two wavefunctions. A compound based on our design principles exhibited a high rate of fluorescence decay and efficient up-conversion of triplet excitons into singlet excited states, leading to both photoluminescence and internal electroluminescence quantum yields of nearly 100%.. |
| 313. | Rong Liu, Ryoichi Ishimatsu, Masayuki Yahiro, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Fluorometric flow-immunoassay for alkylphenol polyethoxylates on a microchip containing a fluorescence detector comprised of an organic light emitting diode and an organic photodiode, TALANTA, 10.1016/j.talanta.2014.10.055, 134, 37-47, 2015.03, A compact fluorescence detector was constructed on a microchip from an organic light emitting diode (OLED) as the light source and an organic photodiode (OPD) as the photo-detector and was used in an immunoassay for allcylphenol polyethoxylates (APE). The OLED based on a terbium complex emitted a sharp light at the main wavelength of 546 nm with a full width at half maximum of 9 nm. The incident photo-to-current conversion efficiency (IPCE) of the OPD fabricated with Fullerene 70(C-70) and tris[4-(5phenylthiopen-2-yephenyll-amine (TPTPA) was approximately 44% for light at a wavelength of 586 nm. The performance of the fluorescence detector was evaluated for the determination of resorufin (lambda(em)= 586 nm) and the photocurrent of the OPD due to the fluorescence of resorufin was proportional to the concentration of resorufin in the range from 0 to 18 mu M with a detection limit (S/N=3) of 0.6 mu M. The fluorescence detector was successfully utilized in a competitive enzyme-linked immunosorbent assay for APE, where an anti-APE antibody was immobilized on the surface of the channel of the Polydimethylsiloxane (PDMS) microchip or on the surface of magnetic microbeads. After an immunoreaction with a sample solution of APE containing a horse radish peroxidase (HRP)-labeled APE, the fluorescence of resorufin generated just after introduction of a mixed solution of Amplex Red and H2O2 was measured using the fluorescence detector. The calibration curve for the photocurrent signals of the OPD due to the fluorescence of resorufin against the logarithmic concentration of APE was sigmoidal in shape. The detection limits defined as IC80 were ca. 1 ppb and ca. 2 ppb, respectively, for the methods using the anti-APE antibody immobilized on the surface of the microchannel and in the case where the antibody was immobilized on the surface of magnetic microbeads. (C) 2014 Elsevier B.V. All rights reserved.. |
| 314. | Katsuyuki Shizu, Motoyuki Uejima, Hiroko Nomura, Tohru Sato, Kazuyoshi Tanaka, Hironori Kaji, Chihaya Adachi, Enhanced Electroluminescence from a Thermally Activated Delayed-Fluorescence Emitter by Suppressing Nonradiative Decay, PHYSICAL REVIEW APPLIED, 10.1103/PhysRevApplied.3.014001, 3, 1, 2015.01, Thermally activated delayed-fluorescence (TADF) is a promising approach for realizing highly efficient organic light-emitting diodes (OLEDs). By controlling the spatial overlap between the frontier orbitals to suppress nonradiative decay, we develop a highly efficient TADF emitter, N-1-[4-(4,6-diphenyl-1,3, 5-triazin-2-yl)phenyl]-N-1-[4-(diphenylamino)-phenyl]-N-4, N-4-diphenylbenzene-1,4-diamine (DPA-TRZ). DPA-TRZ exhibits a photoluminescence quantum efficiency of 100% when doped into a host material, suggesting that nonradiative decay from its excited states is completely suppressed. Transient photoluminescence measurements confirm that DPA-TRZ emits TADF in a doped film. An OLED containing DPA-TRZ as a green emitter shows a maximum external quantum efficiency of 13.8%, which exceeds the theoretical limit for conventional fluorescent OLEDs. This high efficiency results from the effective generation of TADF and suppressed nonradiative decay in DPA-TRZ. Our molecular design strategy based on quantum chemistry provides a rational approach to control radiative and nonradiative decays for optimizing TADF materials.. |
| 315. | Yutaka Noguchi, Hyung-Jun Kim, Ryuta Ishino, Kenichi Goushi, Chihaya Adachi, Yasuo Nakayama, Hisao Ishii, Charge carrier dynamics and degradation phenomena in organic light-emitting diodes doped by a thermally activated delayed fluorescence emitter, ORGANIC ELECTRONICS, 10.1016/j.orgel.2014.12.009, 17, 184-191, 2015.02, We report on the charge carrier dynamics and their degradation phenomena in an organic light-emitting diode (OLED) doped by a thermally activated delayed fluorescence emitter; (4s, 6s)-2,4,5,6-tetra(9H-carbazol-9-yl) isophthalonitrile (4CzIPN). Displacement current measurement (DCM) data revealed the presence of negative interface charge originating from the spontaneous orientation polarization of the electron transport layer (ETL), 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl) benzene. The negative interface charge acts as a hole reservoir and thus confines the recombination zone near the emission layer (EML); 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP):4CzIPN (5 wt%)/ETL interface. By keeping the recombination zone far from the hole transport layer, 4,40-bis[N-(1-naphthyl)-N-phenylamino]- biphenyl (alpha-NPD), a better electroluminescence efficiency is expected because the Dexter energy transfer from the triplet state of 4CzIPN to that of alpha-NPD is suppressed. Moreover, we found an excellent linear relation between the accumulated hole amount and luminance losses owing to device aging. The results are consistent with hole traps originating at the degradation products of CBP as the main factor of device degradation. We suggest device architectures based on the charge carrier dynamics for better efficiency and lifetime. (C) 2014 Elsevier B.V. All rights reserved.. |
| 316. | Daniel Ping-Kuen Tsang, Toshinori Matsushima, Chihaya Adachi, Operational stability enhancement in organic light-emitting diodes with ultrathin Liq interlayers (vol 6, 22463, 2016), SCIENTIFIC REPORTS, 10.1038/srep26921, 6, 26921, 2016.05. |
| 317. | Hiroya Arai, Hajime Nakanotani, Kei Morimoto, Chihaya Adachi, Magnesium-gold binary alloy for organic light-emitting diodes with high corrosion resistance, Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, 10.1116/1.4952408, 34, 4, 2016.07, The authors demonstrate a simple approach to obtain cathodes that have a high resistance against corrosion by water and oxygen and an air-stable work-function of -3.7 eV by doping 10 at. % of gold (Au) into a magnesium (Mg) base metal layer. Organic light-emitting diodes (OLEDs) with the Mg-Au cathodes achieved electroluminescence characteristics that are comparable to those of devices with conventional cathodes such as aluminum (Al) and Mg-silver (Ag). Although OLEDs with Al or Mg-Ag cathodes exhibited a significant reduction of their emissive area when operated in air, the emissive area of the OLEDs with Mg-Au cathodes decreased only 10% after 10 days of operation in ambient air without any specific encapsulation. These results suggest that Mg-Au cathodes can loosen the strict requirements for encapsulation, reducing the number of process steps and cost of OLED fabrication.. |
| 318. | Sae Youn Lee, Chihaya Adachi, Takuma Yasuda, Blue Oleds: High-Efficiency Blue Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence from Phenoxaphosphine and Phenoxathiin Derivatives (Adv. Mater. 23/2016), Advanced Materials, 10.1002/adma.201670160, 28, 23, 4625, 2016.06. |
| 319. | Shota Haseyama, Akitsugu Niwa, Takashi Kobayashi, Takashi Nagase, Kenichi Goushi, Chihaya Adachi, Hiroyoshi Naito, Control of the Singlet-Triplet Energy Gap in a Thermally Activated Delayed Fluorescence Emitter by Using a Polar Host Matrix, NANOSCALE RESEARCH LETTERS, 10.1186/s11671-017-2012-1, 12, 2017.04, The photoluminescence properties of a thermally activated delayed fluorescence emitter, 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN), doped in a host matrix consisting of 1,3-bis(9-carbazolyl) benzene and a polar inert molecule, camphoric anhydride (CA), in various concentrations have been investigated. It is found that the addition of CA stabilizes only the lowest singlet excited state (S-1) of 2CzPN without changing the energy level of the lowest triplet excited state (T-1), leading to a reduction in the energy gap between S-1 and T-1. The maximum reduction of energy gap achieved in this work has been determined to be around 65 meV from the shift of the fluorescence spectrum and the temperature dependence of the photoluminescence decay rate.. |
| 320. | Harunobu Takeda, Michika Takeda, Hiroaki Yoshioka, Hiroaki Minamide, Yuji Oki, Chihaya Adachi, Fluorescence lifetime elongation of thermally activated delayed fluorescence 4CzIPN molecules with encapsulation into zeolitic imidazole frameworks ZIF-11, Optical Materials Express, 10.1364/OME.9.001150, 9, 3, 1150-1160, 2019.03, © 2019 Optical Society of America. Encapsulation of fluorescent directives "thermally activated delayed fluorescence" molecules into a zeolitic imidazole frameworks was proposed, and 4CzIPN molecules were successfully encapsulated into ZIF-11 pores by one step process with a loading efficiency of 0.064 of the proportion of 4CzIPN/ZIF-11. Some Spectroscopic studies such as XRD, UV-Vis, FTIR, THz-TDS and time resolved streak measurement, and the suppression of intramolecular vibrational, rotational and librational motions of 4CzIPN molecules were confirmed. Interestingly, the florescence lifetime of 4CzIPN was considerably elongated from 2.37 ns to 14.8 ns, while the phosphorescence lifetime became a little bit short from 2.15 μs to 1.65 μs. The lifetime differences was thought to be due to the suppression of the 4CzIPN molecules' motion by the close ZIF-11 frameworks that affected the reverse intersystem crossing.. |
| 321. | Shizu, K., Adachi, C., Kaji, H., 【2020-2】Effect of Vibronic Coupling on Correlated Triplet Pair Formation in the Singlet Fission Process of Linked Tetracene Dimers, J. Phys. Chem. A, 124, 18, 3641-3651, 2020.04. |
| 322. | Katsuyuki Shizu, Chihaya Adachi, Hironori Kaji, Visual Understanding of Vibronic Coupling and Quantitative Rate Expression for Singlet Fission in Molecular Aggregates, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20200159, 2020.06. |
| 323. | Ganbaatar Tumen-Ulzii, Chuanjiang Qin, Toshinori Matsushima, Matthew R. Leyden, Umamahesh Balijipalli, Dino Klotz, Chihaya Adachi, Understanding the Degradation of Spiro‐OMeTAD‐Based Perovskite Solar Cells at High Temperature, Solar RRL, 10.1002/solr.202000305, 4, 10, 2000305-2000305, 2020.10. |
| 324. | Ganbaatar Tumen-Ulzii, Toshinori Matsushima, Dino Klotz, Chihaya Adachi, The effect of current density–voltage measurement conditions on the operational stability of hybrid perovskite solar cells, Applied Physics Letters, 10.1063/5.0023622, 117, 10, 103503-103503, 2020.09. |
| 325. | Chihaya Adachi, Atula S. D. Sandanayaka, The Leap from Organic Light-Emitting Diodes to Organic Semiconductor Laser Diodes, CCS Chemistry, 10.31635/ccschem.020.202000327, 2, 4, 1203-1216, 2020.08. |
| 326. | Kentaro Yamamoto, Daisuke Kawaguchi, Tatsuki Abe, Takeshi Komino, Masashi Mamada, Taizo Kabe, Chihaya Adachi, Kensuke Naka, Keiji Tanaka, Surface Segregation of a Star-Shaped Polyhedral Oligomeric Silsesquioxane in a Polymer Matrix, Langmuir, 10.1021/acs.langmuir.0c01785, 36, 33, 9960-9966, 2020.08, A simple way to control only the surface properties of polymer materials, without changing the bulk properties, has long been desired. The segregation behavior when a component with a tiny amount fed into the matrix is thermodynamically enriched at the surface is one of the candidate methods. This capability was examined herein by focusing on a star-shaped polyhedral oligomeric silsesquioxane (s-POSS), where the central POSS unit is tethered to eight isobutyl-substituted POSS cages as a surface modifier. X-ray photoelectron spectroscopy revealed that the surface of a film of poly(methyl methacrylate) (PMMA) was almost completely covered with POSS units by adding just 5 wt % s-POSS to it. The segregated POSS dramatically altered the physical properties such as molecular motion and the mechanical and dielectric responses at the surface of the PMMA film. These findings make it clear that s-POSS is an excellent surface modifier for glassy polymers.. |
| 327. | Buddhika S. B. Karunathilaka, Umamahesh Balijapalli, Chathuranganie A. M. Senevirathne, Seiya Yoshida, Yu Esaki, Kenichi Goushi, Toshinori Matsushima, Atula S. D. Sandanayaka, Chihaya Adachi, Suppression of external quantum efficiency rolloff in organic light emitting diodes by scavenging triplet excitons, Nature Communications, 10.1038/s41467-020-18292-0, 11, 1, 2020.12, Large external quantum efficiency rolloff at high current densities in organic light-emitting diodes (OLEDs) is frequently caused by the quenching of radiative singlet excitons by long-lived triplet excitons [singlet–triplet annihilation (STA)]. In this study, we adopted a triplet scavenging strategy to overcome the aforementioned STA issue. To construct a model system for the triplet scavenging, we selected 2,6-dicyano-1,1-diphenyl-λ5σ4-phosphinine (DCNP) as the emitter and 4,4′-bis[( |
| 328. | Morgan Auffray, Umamahesh Balijapalli, Jean-Charles Ribierre, Youichi Tsuchiya, Chihaya Adachi, Sub-Microsecond TADF Emission in D-D′-A Emitters, Chemistry Letters, 10.1246/cl.200337, 49, 8, 932-935, 2020.08. |
| 329. | Chuanjiang Qin, Atula S. D. Sandanayaka, Chenyang Zhao, Toshinori Matsushima, Dezhong Zhang, Takashi Fujihara, Chihaya Adachi, Stable room-temperature continuous-wave lasing in quasi-2D perovskite films, Nature, 10.1038/s41586-020-2621-1, 585, 7823, 53-57, 2020.09, Organic–inorganic lead halide quasi-two-dimensional (2D) perovskites are promising gain media for lasing applications because of their low cost, tunable colour, excellent stability and solution processability1,2,3. Optically pumped continuous-wave (CW) lasing is highly desired for practical applications in high-density integrated optoelectronics devices and constitutes a key step towards electrically pumped lasers4,5,6. However, CW lasing has not yet been realized at room temperature because of the ‘lasing death’ phenomenon (the abrupt termination of lasing under CW optical pumping), the cause of which remains unknown. Here we study lead halide-based quasi-2D perovskite films with different organic cations and observe that long-lived triplet excitons considerably impede population inversion during amplified spontaneous emission and optically pumped pulsed and CW lasing. Our results indicate that singlet–triplet exciton annihilation is a possible intrinsic mechanism causing lasing death. By using a distributed-feedback cavity with a high quality factor and applying triplet management strategies, we achieve stable green quasi-2D perovskite lasers under CW optical pumping in air at room temperature. We expect that our findings will pave the way to the realization of future current-injection perovskite lasers.. |
| 330. | Emma V. Puttock, Chandana Sampath Kumara Ranasinghe, Mohammad Babazadeh, Junhyuk Jang, David M. Huang, Youichi Tsuchiya, Chihaya Adachi, Paul L. Burn, Paul E. Shaw, Solution-Processed Dendrimer-Based TADF Materials for Deep-Red OLEDs, Macromolecules, 10.1021/acs.macromol.0c02235, 53, 23, 10375-10385, 2020.12. |
| 331. | Van T. N. Mai, Viqar Ahmad, Masashi Mamada, Toshiya Fukunaga, Atul Shukla, Jan Sobus, Gowri Krishnan, Evan G. Moore, Gunther G. Andersson, Chihaya Adachi, Ebinazar B. Namdas, Shih-Chun Lo, Solid cyclooctatetraene-based triplet quencher demonstrating excellent suppression of singlet–triplet annihilation in optical and electrical excitation, Nature Communications, 10.1038/s41467-020-19443-z, 11, 1, 2020.12, Triplet excitons have been identified as the major obstacle to the realisation of organic laser diodes, as accumulation of triplet excitons leads to significant losses under continuous wave (CW) operation and/or electrical excitation. Here, we report the design and synthesis of a solid-state organic triplet quencher, as well as in-depth studies of its dispersion into a solution processable bis-stilbene-based laser dye. By blending the laser dye with 20 wt% of the quencher, negligible effects on the ASE thresholds, but a complete suppression of singlet–triplet annihilation (STA) and a 20-fold increase in excited-state photostability of the laser dye under CW excitation, were achieved. We used small-area OLEDs (0.2 mm2) to demonstrate efficient STA suppression by the quencher in the nanosecond range, supported by simulations to provide insights into the observed STA quenching under electrical excitation. The results demonstrate excellent triplet quenching ability under both optical and electrical excitations in the nanosecond range, coupled with excellent solution processability.. |
| 332. | Yuuhi Ueda, Hajime Nakanotani, Takuya Hosokai, Yuya Tanaka, Hokuto Hamada, Hisao Ishii, Shuhei Santo, Chihaya Adachi, Role of Spontaneous Orientational Polarization in Organic Donor–Acceptor Blends for Exciton Binding, Advanced Optical Materials, 10.1002/adom.202000896, 8, 21, 2000896-2000896, 2020.11, Electron-hole pairs at the interface between electron-donating and electron-accepting molecules form charge-transfer excitons (CTEs) via Coulomb attraction. Generally, the attraction energy of the CTE is weaker than that of the Frenkel exciton because of spatial separation of the charge pair; thus, the binding of the CTE is expected to be sensitive to an electric field. Here, the shielding of the binding energy of the CTEs by an internal electric field induced by spontaneous orientation polarization (SOP) of the solid-state donor-acceptor blend film is reported. When the blend film forms a large SOP, the photogenerated CTEs spontaneously dissociate without an external electric field, resulting in carrier diffusion and carrier lifetimes that are in the milliseconds or longer. In the absence of a large SOP, the CTEs preferentially form exciplexes that quickly release their energy as light rather than dissociation. Hence, the control of SOP in the donor-acceptor blend films can provide new insights into exciton binding and facilitate the development of tailored high-performance organic semiconductor devices.. |
| 333. | Masaki Tanaka, Ryo Nagata, Hajime Nakanotani, Chihaya Adachi, Precise Exciton Management of Quaternary Emission Layers for Highly Stable Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence, ACS Applied Materials & Interfaces, 10.1021/acsami.0c15208, 12, 45, 50668-50674, 2020.11, Simultaneous achievement of both high electroluminescence efficiency and high operational stability in organic light-emitting diodes (OLEDs) is required for their use in various practical applications. Although OLEDs based on thermally activated delayed fluorescence-Assisted fluorescence (TAF) are considered to possess a promising device architecture to exploit the full potential of OLEDs, the operational stability of such systems still requires further improvement. In this study, a quaternary emission layer consisting of a combination of TAF and mixed-host systems is developed. OLEDs containing this emission layer show improved operational stability through the management of exciton generation processes while maintaining high electroluminescence efficiency. Furthermore, a gradient of the mixed ratio of the co-host matrix is used to optimize the recombination zone profile in the emission layer, leading to 17 times improvement of the operational lifetime compared with that of the corresponding single-host-based device. This research provides a simple and general method to develop highly stable TAF-OLEDs.. |
| 334. | Masayuki Yokoyama, Youichi Tsuchiya, Hajime Nakanotani, Chihaya Adachi, Partial Modification of Electron-withdrawing Groups in Thermally-activated Delayed Fluorescence Materials Aimed to Improve Efficiency and Stability, Chemistry Letters, 10.1246/cl.200435, 49, 10, 1189-1193, 2020.10, Highly efficient and stable blue-green thermally-activated delayed fluorescence (TADF) molecules with trifluoromethyl (CF3) groups were developed. Partial modification with CF3 groups at the appropriate position of the donor moiety improved the luminescence efficiency and excited state stability. OLEDs using modified emitters showed improved EQE and operational lifetime compared with unmodified examples.. |
| 335. | Satoru Watanabe, Ganbaatar Tumen-Ulzii, Tai Cheng, Toshinori Matsushima, Chihaya Adachi, Origin and Suppression of External Quantum Efficiency Roll-Off in Quasi-Two-Dimensional Metal Halide Perovskite Light-Emitting Diodes, The Journal of Physical Chemistry C, 10.1021/acs.jpcc.0c09241, 124, 50, 27422-27428, 2020.12. |
| 336. | Wenbo Li, Zhaoning Li, Changfeng Si, Michael Y. Wong, Kazuya Jinnai, Abhishek Kumar Gupta, Ryota Kabe, Chihaya Adachi, Wei Huang, Eli Zysman‐Colman, Ifor D. W. Samuel, Organic Long‐Persistent Luminescence from a Thermally Activated Delayed Fluorescence Compound, Advanced Materials, 10.1002/adma.202003911, 32, 45, 2003911-2003911, 2020.11. |
| 337. | Ghaida Alosaimi, Chuanjiang Qin, Toshinori Matsushima, Chihaya Adachi, Jan Seidel, Nanoscale Electronic Properties of Triplet-State-Engineered Halide Perovskites, The Journal of Physical Chemistry C, 10.1021/acs.jpcc.0c03996, 124, 27, 14811-14817, 2020.07. |
| 338. | Atul Shukla, Van T. N. Mai, A. M. Chathuranganie Senevirathne, Ilene Allison, Sarah K. M. McGregor, Romain J. Lepage, Michael Wood, Toshinori Matsushima, Evan G. Moore, Elizabeth H. Krenske, Atula S. D. Sandanayaka, Chihaya Adachi, Ebinazar B. Namdas, Shih‐Chun Lo, Low Amplified Spontaneous Emission and Lasing Thresholds from Hybrids of Fluorenes and Vinylphenylcarbazole, Advanced Optical Materials, 10.1002/adom.202000784, 8, 20, 2000784-2000784, 2020.10. |
| 339. | Van T. N. Mai, Atul Shukla, A. M. Chathuranganie Senevirathne, Ilene Allison, Hyunsoo Lim, Romain J. Lepage, Sarah K. M. McGregor, Michael Wood, Toshinori Matsushima, Evan G. Moore, Elizabeth H. Krenske, Atula S. D. Sandanayaka, Chihaya Adachi, Ebinazar B. Namdas, Shih‐Chun Lo, Lasing Operation under Long‐Pulse Excitation in Solution‐Processed Organic Gain Medium: Toward CW Lasing in Organic Semiconductors, Advanced Optical Materials, 10.1002/adom.202001234, 8, 21, 2001234-2001234, 2020.11. |
| 340. | Tai Cheng, Ganbaatar Tumen-Ulzii, Dino Klotz, Satoru Watanabe, Toshinori Matsushima, Chihaya Adachi, Ion Migration-Induced Degradation and Efficiency Roll-off in Quasi-2D Perovskite Light-Emitting Diodes, ACS Applied Materials & Interfaces, 10.1021/acsami.0c06737, 12, 29, 33004-33013, 2020.07. |
| 341. | Yuushi Shimoda, Kiyoshi Miyata, Masaki Saigo, Youichi Tsuchiya, Chihaya Adachi, Ken Onda, Intramolecular-rotation driven triplet-to-singlet upconversion and fluctuation induced fluorescence activation in linearly connected donor–acceptor molecules, The Journal of Chemical Physics, 10.1063/5.0029608, 153, 20, 204702-204702, 2020.11. |
| 342. | Yongsheng Hu, Fatima Bencheikh, Sébastien Chénais, Sébastien Forget, Xingyuan Liu, Chihaya Adachi, High performance planar microcavity organic semiconductor lasers based on thermally evaporated top distributed Bragg reflector, Applied Physics Letters, 10.1063/5.0016052, 117, 15, 153301-153301, 2020.10. |
| 343. | Lin-Song Cui, Alexander J. Gillett, Shou-Feng Zhang, Hao Ye, Yuan Liu, Xian-Kai Chen, Ze-Sen Lin, Emrys W. Evans, William K. Myers, Tanya K. Ronson, Hajime Nakanotani, Sebastian Reineke, Jean-Luc Bredas, Chihaya Adachi, Richard H. Friend, Fast spin-flip enables efficient and stable organic electroluminescence from charge-transfer states, Nature Photonics, 10.1038/s41566-020-0668-z, 14, 10, 636-642, 2020.10. |
| 344. | Minghan Cai, Morgan Auffray, Dongdong Zhang, Yuewei Zhang, Ryo Nagata, Zesen Lin, Xun Tang, Chin-Yiu Chan, Yi-Ting Lee, Tianyu Huang, Xiaozeng Song, Youichi Tsuchiya, Chihaya Adachi, Lian Duan, Enhancing spin-orbital coupling in deep-blue/blue TADF emitters by minimizing the distance from the heteroatoms in donors to acceptors, Chemical Engineering Journal, 10.1016/j.cej.2020.127591, 127591-127591, 2020.11. |
| 345. | Anubha Bilgaiyan, Fahed Elsamnah, Hiroshi Ishidai, Chang-Hoon Shim, Muhamad Affiq Bin Misran, Chihaya Adachi, Reiji Hattori, Enhancing Small-Molecule Organic Photodetector Performance for Reflectance-Mode Photoplethysmography Sensor Applications, ACS Applied Electronic Materials, 10.1021/acsaelm.0c00082, 2, 5, 1280-1288, 2020.05, Organic photodetector performance for enhancing the sensing abilities of an organic photoplethysmography sensor was investigated. The optimized organic photodetector with an anode interlayer and a cathode interlayer showed a reverse dark current density of 22 nA cm(-2) at -2 V and an external quantum efficiency of 53.3% at 0 V. This organic photodetector was fabricated monolithically with an organic light-emitting diode on a glass substrate to achieve a reflectance-mode photoplethysmography sensor, demonstrating the impact of organic photodetector device performance on the measured photoplethysmography signal for sensing applications. Furthermore, we estimated the optimal sensor design for circular geometry in terms of device area and distance between the organic light-emitting diode and organic photodetector to maximize the signal-to-noise ratio and lower the power consumption of organic photoplethysmography sensor devices. For the most favorable photoplethysmography sensor design, a signal strength of 130 mV with 600 mu W power consumption was measured.. |
| 346. | Xun Tang, Yi-Ting Lee, Zhao Feng, Soo Young Ko, Jeong Weon Wu, Virginie Placide, Jean-Charles Ribierre, Anthony D’Aléo, Chihaya Adachi, Color-Tunable Low-Threshold Amplified Spontaneous Emission from Yellow to Near-Infrared (NIR) Based on Donor–Spacer–Acceptor–Spacer–Donor Linear Dyes, ACS Materials Letters, 10.1021/acsmaterialslett.0c00421, 2, 12, 1567-1574, 2020.12. |
| 347. | Hajime Nakanotani, Youichi Tsuchiya, Chihaya Adachi, Thermally-activated delayed fluorescence for light-emitting devices, Chemistry Letters, 10.1246/cl.200915, 2021.01. |
| 348. | Youichi Tsuchiya, Yuma Ishikawa, Sang‐Hoon Lee, Xian‐Kai Chen, Jean‐Luc Brédas, Hajime Nakanotani, Chihaya Adachi, Thermally Activated Delayed Fluorescence Properties of Trioxoazatriangulene Derivatives Modified with Electron Donating Groups, Advanced Optical Materials, 10.1002/adom.202002174, 9, 14, 2002174-2002174, 2021.03, With the aim of achieving high-performance thermally activated delayed fluorescence, a series of trioxoazatriangulene derivatives are systematically developed by modifying the donor substituents. The emission colors are shifted from green to greenish-yellow and to yellow with rather broad spectral widths of 70-95 nm by introducing carbazole, triphenylamine, or diphenylamine donor units, indicating that each emission originates from a charge-transfer transition. On the other hand, the trioxoazatriangulene modified with three diphenylamines shows orange emission with a narrow emission spectrum (45 nm), suggesting that the transition mainly originates from a multiple resonance effect.. |
| 349. | Masashi Mamada, Kenichi Goushi, Ryota Nakamura, Hironori Kaji, Chihaya Adachi, Synthesis and Characterization of 5,5′-Bitetracene, Chemistry Letters, 10.1246/cl.200909, 50, 4, 800-803, 2021.04, A tetracene dimer, 5,5'-bitetracene (55BT), has successfully been synthesized for the first time and its structure was confirmed by X-ray single crystal analysis. The electrochemical and optical properties of 55BT were investigated and compared to those of tetracene. Although the photoluminescence quantum yield of 55BT was slightly higher than that of tetracene, the results of the transient absorption spectroscopy suggested triplet formation by singlet fission in solution.. |
| 350. | Chin-Yiu Chan, Masaki Tanaka, Yi-Ting Lee, Yiu-Wing Wong, Hajime Nakanotani, Takuji Hatakeyama, Chihaya Adachi, Stable pure-blue hyperfluorescence organic light-emitting diodes with high-efficiency and narrow emission, Nature Photonics, 10.1038/s41566-020-00745-z, 15, 3, 203-207, 2021.03. |
| 351. | Reiko Aoki, Ryutaro Komatsu, Kenichi Goushi, Masashi Mamada, Soo Young Ko, Jeong Weon Wu, Virginie Placide, Anthony D'Aléo, Chihaya Adachi, Realizing Near‐Infrared Laser Dyes through a Shift in Excited‐State Absorption, Advanced Optical Materials, 10.1002/adom.202001947, 9, 6, 2001947-2001947, 2021.03, The development of near-infrared (NIR) light sources has attracted much interest due to their attractive applications, such as biosensing and light detection and ranging (LiDAR). In particular, organic semiconductor laser diodes with NIR emission are emerging as a next generation technology. However, organic NIR emitters have generally suffered from a low quantum yield, which has resulted in only a few examples of organic solid-state NIR lasers. In this study, the authors demonstrate a highly efficient NIR emitter based on a boron difluoride curcuminoid structure, which shows a high photoluminescence (PL) quantum yield (phi(PL)) at >700 nm and a high fluorescence radiative rate constant in a solid-state film. Amplified spontaneous emission and lasing occurs at >800 nm with very low thresholds. The large redshift of the stimulated emission is attributed to the transition from the lowest excited state to the different vibrational levels of the ground state owing to the overlap between the emission and the singlet-singlet excited-state absorption.. |
| 352. | Pachaiyappan Rajamalli, Dongyang Chen, Subeesh Madayanad Suresh, Youichi Tsuchiya, Chihaya Adachi, Eli Zysman‐Colman, Planar and Rigid Pyrazine‐Based TADF Emitter for Deep Blue Bright Organic Light‐Emitting Diodes, European Journal of Organic Chemistry, 10.1002/ejoc.202100086, 2021.03. |
| 353. | Xiaolei Zhu, Cheriehan Hessin, Aude Salamé, Lydia Sosa‐Vargas, David Kreher, Chihaya Adachi, Anna Proust, Pierre Mialane, Jérome Marrot, Aude Bouchet, Michel Sliwa, Stéphane Méry, Benoît Heinrich, Fabrice Mathevet, Guillaume Izzet, Photoactive Organic/Inorganic Hybrid Materials with Nanosegregated Donor–Acceptor Arrays, Angewandte Chemie International Edition, 10.1002/anie.202014319, 60, 15, 8419-8424, 2021.04. |
| 354. | Chathuranganie A. M. Senevirathne, Atula S. D. Sandanayaka, Buddhika S. B. Karunathilaka, Takashi Fujihara, Fatima Bencheikh, Chuanjiang Qin, Kenichi Goushi, Toshinori Matsushima, Chihaya Adachi, Markedly Improved Performance of Optically Pumped Organic Lasers with Two-Dimensional Distributed-Feedback Gratings, ACS Photonics, 10.1021/acsphotonics.0c01728, 8, 5, 1324-1334, 2021.03, Continuous-wave (CW) lasing is still difficult to realize in organic laser dyes, one reason being the thermal degradation caused by intense photoexcitation. A decrease in laser threshold suppresses the thermal degradation and, therefore, leads to long-lasting lasing from organic laser dyes. Here, we show that it is possible to decrease the laser thresholds by combining the organic laser dye 4,4-bis[(N-carbazole)styryl]biphenyl, which has a small spectral overlap between the laser emission and the excited-state triplet absorption, with two-dimensional (2D) distributed-feedback (DFB) gratings. We used second-order 2D cross double and square lattice DFB gratings, which offer light feedback in two orthogonal directions, and second-order and mixed-order circular DFB gratings, which offer light feedback in radial directions. Among these grating structures, the mixed-order circular DFB grating structure led to the lowest lasing threshold of similar to 0.015 mu J cm(-2) under short-pulse photoexcitation because of the excellent optical feedback. Moreover, a low average-power threshold of 10 W cm(-2) (a peak-power threshold of 1 kW cm-2) was obtained when laser devices with this grating structure were operated under 1 s of long-pulse photoexcitation with a repetition rate of 0.01 Hz. Additionally, using the mixed-order circular DFB grating structure improved the laser stability under CW photoexcitation since shorter exciton lifetimes in the optical resonator suppress the chemical decomposition. These results demonstrate the importance of choosing an optical resonator structure for improving organic laser performance.. |
| 355. | Xuelong Liu, Chin-Yiu Chan, Fabrice Mathevet, Masashi Mamada, Youichi Tsuchiya, Yi-Ting Lee, Hajime Nakanotani, Shinichiro Kobayashi, Masayuki Shiochi, Chihaya Adachi, Isotope Effect of Host Material on Device Stability of Thermally Activated Delayed Fluorescence Organic Light‐Emitting Diodes, Small Science, 10.1002/smsc.202000057, 1, 4, 2000057-2000057, 2021.04. |
| 356. | Yi‐Ting Lee, Chin‐Yiu Chan, Masaki Tanaka, Masashi Mamada, Umamahesh Balijapalli, Youichi Tsuchiya, Hajime Nakanotani, Takuji Hatakeyama, Chihaya Adachi, Investigating HOMO Energy Levels of Terminal Emitters for Realizing High‐Brightness and Stable TADF‐Assisted Fluorescence Organic Light‐Emitting Diodes, Advanced Electronic Materials, 10.1002/aelm.202001090, 7, 4, 2001090-2001090, 2021.04. |
| 357. | Aziz Khan, Xun Tang, Cheng Zhong, Qiang Wang, Sheng‐Yi Yang, Fan‐Cheng Kong, Shuai Yuan, Atula S. D. Sandanayaka, Chihaya Adachi, Zuo‐Quan Jiang, Liang‐Sheng Liao, Intramolecular‐Locked High Efficiency Ultrapure Violet‐Blue (CIE‐y Advanced Functional Materials, 10.1002/adfm.202009488, 31, 15, 2009488-2009488, 2021.04. |
| 358. | Umamahesh Balijapalli, Ryo Nagata, Nishiki Yamada, Hajime Nakanotani, Masaki Tanaka, Anthony D'Aléo, Virginie Placide, Masashi Mamada, Youichi Tsuchiya, Chihaya Adachi, Highly Efficient Near‐Infrared Electrofluorescence from a Thermally Activated Delayed Fluorescence Molecule, Angewandte Chemie International Edition, 10.1002/anie.202016089, 60, 15, 8477-8482, 2021.04. |
| 359. | Yuto Kage, Seongsoo Kang, Shigeki Mori, Masashi Mamada, Chihaya Adachi, Dongho Kim, Hiroyuki Furuta, Soji Shimizu, An Electron‐Accepting aza‐BODIPY‐Based Donor–Acceptor–Donor Architecture for Bright NIR Emission, Chemistry – A European Journal, 10.1002/chem.202005360, 27, 16, 5259-5267, 2021.03, A bright near-infrared (NIR) fluorescent molecule was developed based on the donor–acceptor–donor (D–A–D) approach using an aza-BODIPY analog called pyrrolopyrrole aza-BODIPY (PPAB) as an electron-accepting chromophore. Directly introducing electron-donating triphenylamine (TPA) to develop a D–A–D structure caused redshifts of absorption and emission of PPAB into the NIR region with an enhanced fluorescence brightness of up to 5.2×104 m−1 cm−1, whereas inserting a phenylene linker between the TPA donor and the PPAB acceptor induced solvatochromic behavior in emission. Transient absorption spectra and theoretical calculations revealed the presence of a highly emissive hybridized locally excited and charge-transfer state in the former case and the contribution of the dark charge-separated state to the excited state in the latter case. The bright D–A–D PPAB as a novel emitter resulted in a NIR electroluminescence with a high external quantum efficiency of 3.7 % and a low amplified spontaneous emission threshold of ca. 80 μJ cm−2, indicating the high potential for NIR optoelectronic applications.. |
| 360. | Komiyama H, Adachi C, Yasuda T, Star-shaped and linear π-conjugated oligomers consisting of a tetrathienoanthracene core and multiple diketopyrrolopyrrole arms for organic solar cells., Beilstein journal of organic chemistry, 10.3762/bjoc.12.142, 12, 1459-1466, 2016.07, [URL]. |
| 361. | Hin Wai Mo, Youichi Tsuchiya, Yan Geng, Takehiro Sagawa, Chika Kikuchi, Hajime Nakanotani, Fuyuki Ito, Chihaya Adachi, Tunable OLEDs Color Tuning of Avobenzone Boron Difluoride as an Emitter to Achieve Full-Color Emission (Adv. Funct. Mater. 37/2016), Advanced Functional Materials, 10.1002/adfm.201670245, 26, 37, 2016.10, [URL]. |
| 362. | Toshinori Matsushima, Takashi Fujihara, Chuanjiang Qin, Shinobu Terakawa, Yu Esaki, Sunbin Hwang, Atula S.D. Sandanayaka, William J. Potscavage, Chihaya Adachi, Morphological control of organic-inorganic perovskite layers by hot isostatic pressing for efficient planar solar cells, Journal of Materials Chemistry A, 10.1039/c5ta03796d, 3, 34, 17780-17787, 2015.07, [URL], Morphological control of organic-inorganic perovskite layers is crucial for efficient planar solar cells. In this study, we show that hot isostatic pressing (HIP) of perovskite layers using a pressure of 200 MPa in 90°C water is very effective for improving the perovskite film morphology. After HIP treatment, undesirable pin holes and spatial gaps between crystals in the perovskite layers were significantly reduced. Improved crystallinity and enhanced diffusion lengths for both electrons and holes were also confirmed in the HIP-treated perovskite layers. Solar cells containing the perovskite layers as light absorbers were fabricated and characterized under simulated solar light (AM1.5G, 100 mW cm-2). The HIP treatment induced a marked enhancement of short-circuit current density, open-circuit voltage, fill factor, and power conversion efficiency because of the improved morphology and crystallinity and enhanced carrier diffusion. The HIP-treated solar cells achieved efficiencies of 10.6 ± 0.7%, which are about 1.5 times higher than those of the untreated solar cells (7.20 ± 0.59%).. |
| 363. | Jinfeng Zhang, Wencheng Chen, Rui Chen, Xiao Ke Liu, Yuan Xiong, Stephen V. Kershaw, Andrey L. Rogach, Chihaya Adachi, Xiaohong Zhang, Chun Sing Lee, Organic nanostructures of thermally activated delayed fluorescent emitters with enhanced intersystem crossing as novel metal-free photosensitizers, Chemical Communications, 10.1039/c6cc05130h, 52, 79, 11744-11747, 2016.01, [URL], We applied organic nanostructures based on thermally activated delayed fluorescent (TADF) emitters for singlet oxygen generation. Due to the extremely small energy gaps between the excited singlet states (S1) and triplet states (T1) of these heavy-metal-free organic nanostructures, intersystem conversion between S1 and T1 can occur easily. This strategy also works well for exciplex-type TADF emitters prepared by mixing suitable donors and acceptors which have no TADF characteristics themselves.. |
| 364. | Li Zhao, Takeshi Komino, Dae Hyeon Kim, Muhammad Hasnan Sazzad, Delphine Pitrat, Jean Christophe Mulatier, Chantal Andraud, Jean Charles Ribierre, Chihaya Adachi, Horizontal molecular orientation of light-emitting oligofluorenes in spin-coated glassy organic thin films, Journal of Materials Chemistry C, 10.1039/c6tc02861f, 4, 48, 11557-11565, 2016.01, [URL], Horizontal orientation of light-emitting chromophores plays a critical role in the light outcoupling efficiency and the overall performances of organic light-emitting diodes. Here, we demonstrate that such a horizontal orientation of light-emitting molecules can be achieved in solution-processed blends containing highly fluorescent oligofluorenes dispersed into various small molecule host materials. The influences of the host material, the solvent used for the spin-coating, the doping concentration of the oligofluorenes and the oligofluorene chemical structure on these orientational processes are investigated using variable angle spectroscopic ellipsometry and angle-dependent photoluminescence measurements. By clarifying the roles played by these parameters in the horizontal orientation of the emitters, the results provide crucial insights into these molecular orientational processes in spin-coated glassy organic thin films, which should be relevant for the development of high-efficiency solution-processed organic light-emitting diodes in the near future.. |
| 365. | Calvyn T. Howells, Khalid Marbou, Haeri Kim, Kwang Jin Lee, Benoît Heinrich, Sang Jun Kim, Aiko Nakao, Tetsua Aoyama, Seiichi Furukawa, Ju Hyung Kim, Eunsun Kim, Fabrice Mathevet, Stéphane Mery, Ifor D.W. Samuel, Amal Al Ghaferi, Marcus S. Dahlem, Masanobu Uchiyama, Sang Youl Kim, Jeong Weon Wu, Jean Charles Ribierre, Chihaya Adachi, Dong Wook Kim, Pascal André, Enhanced organic solar cells efficiency through electronic and electro-optic effects resulting from charge transfers in polymer hole transport blends, Journal of Materials Chemistry A, 10.1039/c6ta00677a, 4, 11, 4252-4263, 2016.01, [URL], We demonstrate that blending fluorinated molecules in PEDOT:PSS hole transport layers (HTL) induces charge transfers which impact on both charge extraction and photogeneration within organic photovoltaic (OPV) devices. OPVs fabricated with modified HTL and two photoactive polymer blends led systematically to power conversion efficiencies (PCE) increases, with PTB7:PC70BM blend exhibiting PCE of ∼8.3%, i.e. ∼15% increase compared to pristine HTL devices. A reduced device-to-device characteristics variations was also noticed when fluorinated additives were used to modify the PEDOT:PSS. Shading lights onto the effect of HTL fluorination, we show that the morphology of the polymer:PCBM blends remains surprisingly unaffected by the fluorinated HTL surface energy but that, instead, the OPVs are impacted not only by the HTL electronic properties (work function, dipole layer, open circuit voltage, charge transfer dynamic) but also by alteration of the complex refractive indices (photogeneration, short circuit current density, external quantum efficiencies, electro-optic modelling). Both mechanisms find their origin in fluorination induced charge transfers. This work points towards fluorination as a promising strategy toward combining both external quantum efficiency modulation and power conversion efficiency enhancement in OPVs. Charge transfers could also be used more broadly to tune the optical constants and electric field distribution, as well as to reduce interfacial charge recombinations within OPVs.. |
| 366. | Cui LS, Kim JU, Nomura H, Nakanotani H, Adachi C, Corrigendum: Benzimidazobenzothiazole-based Bipolar Hosts to Harvest Nearly All of the Excitons from Blue Delayed Fluorescence and Phosphorescent Organic Light-Emitting Diodes., Angewandte Chemie (International ed. in English), 10.1002/anie.201605553, 55, 40, 12136, 2016.09, [URL]. |
| 367. | In Seob Park, Masaki Numata, Chihaya Adachi, Takuma Yasuda, A Phenazaborin-Based High-Efficiency Blue Delayed Fluorescence Material, BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 10.1246/bcsj.20150399, 89, 3, 375-377, 2016.03, [URL], A highly efficient blue thermally activated delayed fluorescence (TADF) material based on phenazaborin and spiroacridan units was developed. A blue-emitting organic light-emitting diode containing the phenazaborin derivative as a TADF emitter exhibited a high external electro-luminescence quantum efficiency of 18.2%.. |
| 368. | Yun Li, Jiao Jiao Liang, Hong Cheng Li, Lin Song Cui, Man Keung Fung, Stephen Barlow, Seth R. Marder, Chihaya Adachi, Zuo Quan Jiang, Liang Sheng Liao, The role of fluorine-substitution on the π-bridge in constructing effective thermally activated delayed fluorescence molecules, Journal of Materials Chemistry C, 10.1039/c8tc01158c, 6, 20, 5536-5541, 2018, [URL], Two thermally activated delayed fluorescence (TADF) emitters 9′-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)-2-fluorophenyl)-9′H-9,3′:6′,9′′-tercarbazole (TCTZ-F) and 9′-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)-2,6-difluorophenyl)-9′H-9,3′:6′,9′′-tercarbazole (TCTZ-2F) were synthesized and compared to the previously reported molecule 9′-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9′H-9,3′:6′,9′′-tercarbazole (TCTZ) to explore the possible effects of the fluorine atom(s) on the molecular conformation, electronic coupling between the donor and acceptor groups, and consequently the photophysical behavior of the emitters. Specifically, the TCTZ-F molecule was calculated to have a smaller dihedral angle than TCTZ-2F and a smaller S1-T1 gap than TCTZ, which led it to have the highest photoluminescence quantum yield (PLQY) among this series of compounds. An OLED fabricated with TCTZ-F as the emitter achieved the highest external quantum efficiencies (22.5%) of this series, indicating that fluorination can play a useful role in TADF emitters.. |
| 369. | Ikbal Marghad, Fatima Bencheikh, Chao Wang, Sophia Manolikakes, Alice Rérat, Corinne Gosmini, Dae Hyeon Kim, Jean Charles Ribierre, Chihaya Adachi, Control of the dual emission from a thermally activated delayed fluorescence emitter containing phenothiazine units in organic light-emitting diodes, RSC Advances, 10.1039/c8ra10393c, 9, 8, 4336-4343, 2019, [URL], The development of single-component organic dual light-emitting molecules is of interest for a range of applications including white organic light-emitting diodes. Herein, a new thermally-activated delayed fluorescent molecule containing 4,6-bis-phenyl phenothiazine as donor units and 2-thiophene-1,3,5-triazine as acceptor unit was synthesized using a simple cost-effective method. This compound shows two stable molecular conformations due to the presence of the phenothiazine units in its molecular structure. These conformers exhibit different photophysical properties in both solution and thin films. The electroluminescence properties of this novel emitter were then examined in organic light-emitting diodes and the results provide useful insights into the influence of the device architecture on the dual emission characteristics. The experimental results were consistent with the optical simulations and the optimized architecture led to the fabrication of electroluminescent devices with an external quantum efficiency of 11.5% and a maximum luminance value of 10370 cd m -2 .. |
| 370. | Takahiko Yamanaka, Hajime Nakanotani, Shigeo Hara, Toru Hirohata, Chihaya Adachi, Near-infrared organic light-emitting diodes for biosensing with high operating stability, APPLIED PHYSICS EXPRESS, 10.7567/APEX.10.074101, 10, 7, 2017.07, [URL], We demonstrate highly stable NIR organic light-emitting diodes (OLEDs) based on a system using excitonic energy transfer from thermally activated delay fluorescence molecules to NIR fluorophores. The NIR OLEDs showed an electroluminescence peak at 780nm and robust operational stability with 2% loss of the initial radiant flux after 1000 h under a constant current density of 10mA/cm(2). The variation of hemoglobin oxygen saturation can be detected using the NIR OLEDs as a light source. (C) 2017 The Japan Society of Applied Physics. |
| 371. | Matthew R. Leyden, Lingqiang Meng, Yan Jiang, Luis K. Ono, Longbin Qiu, Emilio J. Juarez-Perez, Chuanjiang Qin, Chihaya Adachi, Yabing Qi, Methylammonium Lead Bromide Perovskite Light-Emitting Diodes by Chemical Vapor Deposition, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 10.1021/acs.jpclett.7b01093, 8, 14, 3193-3198, 2017.07, [URL], Organo-lead-halide perovskites are promising materials for optoelectronic applications. Perovskite solar cells have reached power conversion efficiencies of over 22%, and perovskite light-emitting diodes have recently achieved over 11% external quantum efficiency. To date, most research on perovskite light-emitting diodes has focused on solution-processed films. There are many advantages of a vapor-based growth process to prepare perovskites, including ease of patterning, ability to batch process, and material compatibility. We investigated an all-vapor perovskite growth process by chemical vapor deposition and demonstrated luminance up to 560 cd/m(2).. |
| 372. | Suzuki, K, Adachi, C, Kaji, H, 【2017-12】Solution-processable thermally activated delayed fluorescence emitters for application in organic light emitting diodes, J. Soc. Inf. Disp., 10.1002/jsid.598, 25, 8, 480-485, 2017.08, [URL]. |
| 373. | Hasegawa, Yuri, Minami, Hayato, Kanada, Satoru, Yamada, Yoichi, Sasaki, Masahiro, Hosokai, Takuya, Nakanotani, Hajime, Adachi, Chihaya, Well-ordered films of disk-shaped thermally activated delayed fluorescence (TADF) molecules, JOURNAL OF PHOTONICS FOR ENERGY, 10.1117/1.JPE.8.032110, 8, 3, 032110, 2018.07, [URL], We fabricated well-ordered, crystalline mono-and multilayers of disk-shaped thermally activated delayed fluorescence (TADF) molecules such as 4CzIPN, 2CzPN, and 5CzBN. The slow deposition of these molecules on flat substrates such as Ag(111) at room temperature resulted in the formation of well-ordered and homogeneous monolayers. Moreover, the multilayer of the 4CzIPN was also found to be well-ordered and flat when deposited on highly oriented pyrolytic graphite (HOPG). The electronic states of the crystalline monolayer and multilayer of 4CzIPN were found to be nearly the same, suggesting that the electronic states of both layers are not altered significantly by adsorption on substrates. Indeed, we also confirmed the delayed fluorescence from the crystalline multilayer of 4CzIPN on the HOPG substrate even in an ambient condition. These results show promising applications of crystalline films of disk-shaped TADF-molecules such as 4CzIPN for organic light-emitting diodes devices with high outcoupling efficiency. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE). |
| 374. | Takuya Hosokai, Hiroki Noda, Hajime Nakanotani, Takanori Nawata, Yasuo Nakayama, Hiroyuki Matsuzaki, Chihaya Adachi, Solvent-dependent investigation of carbazole benzonitrile derivatives Does the le 3 - CT 1 energy gap facilitate thermally activated delayed fluorescence?, Journal of Photonics for Energy, 10.1117/1.JPE.8.032102, 8, 3, 2018.07, [URL], The photophysical properties of six types of carbazole benzonitrile (CzBN) derivatives are investigated in different solvents to examine the thermally activated delayed fluorescence (TADF) activation via reducing the energy gap between the singlet charge-transfer and triplet locally excited states, ΔEST(LE). Relative to the ΔEST(LE) values for the CzBN derivatives in the low polarity solvent toluene (ϵ∼2), a reduction of ΔEST(LE) for the CzBN derivatives in the polar solvent acetonitrile (ϵ∼37) was confirmed while maintaining fairly constant ΔEST values. Notably, TADF activation was observed in acetonitrile for some CzBN derivatives that are TADF inactive in toluene. A numerical analysis of various rate constants revealed the cause of TADF activation as an increase in the reverse intersystem crossing rate and a suppression of the non-radiative decay rate of the triplet states. The positive effect of ΔEST(LE) was limited, however, as an excessive decrease in ΔEST(LE) facilitates the nonradiative deactivation of the triplet states, leading to a loss of the TADF efficiency. This paper shows that ΔEST(LE) provides a measure of TADF activation and that appropriate regulation of ΔEST(LE) is required to achieve high TADF efficiency.. |
| 375. | Youichi Tsuchiya, Koudai Ikesue, Hajime Nakanotani, Chihaya Adachi, Photostable and highly emissive glassy organic dots exhibiting thermally activated delayed fluorescence, Chemical Communications, 10.1039/c9cc01420a, 55, 36, 5215-5218, 2019.01, [URL], Organic nanoparticles (O-dots) with a high photoluminescence quantum yield (94%) and long-lived delayed emission (3.1 μs) originating from thermally activated delayed fluorescence (TADF) were developed as glassy state particles using an oil in water emulsion under high pressure ( |
| 376. | Kazuya Jinnai, Naohiro Nishimura, Ryota Kabe, Chihaya Adachi, Fabrication-method Independence of Organic Long-persistent Luminescence Performance, Chemistry Letters, 10.1246/cl.180949, 48, 3, 270, 2019.03, [URL]. |
| 377. | Afshin Shahalizad, Dae Hyeon Kim, Sanyasi Rao Bobbara, Youichi Tsuchiya, Anthony D'Aléo, Chantal Andraud, Jean Charles Maurice Ribierre, Jean Michel Nunzi, Chihaya Adachi, Enhanced near-infrared electroluminescence from a neodymium complex in organic light-emitting diodes with a solution-processed exciplex host, Applied Physics Letters, 10.1063/1.5054721, 114, 3, 2019.01, [URL], We report enhanced near-infrared (NIR) electroluminescence from a Nd 3+ -complex with thenoyltrifluoroacetone and 1,10-phenanthroline ligands. The NIR-emitting complex was blended into an exciplex-forming co-host system comprising 2,7-bis(diphenylphosphoryl)-9,9′-spirobifluorene as the electron transport material and 4,4′,4″-tris(carbazol-9-yl)triphenylamine as the hole transport material in solution-processed small molecule organic light-emitting diodes (OLEDs). This binary ambipolar host system favors direct charge trapping and exciton formation on the Nd 3+ -complex molecules. Efficient energy transfer from the singlet and triplet exciplexes formed between the host molecules to the Nd 3+ ions contributes to the enhanced luminescence efficiency. The photoluminescence quantum yield of this blend is 1.2%, and the optimized OLED shows a maximum electroluminescence external quantum efficiency of 0.034%. The device also exhibits a low efficiency roll-off of only 12% over a current density range of 100 mA/cm 2 , due to the reduced triplet-polaron annihilation.. |
| 378. | Harunobu Takeda, Michika Takeda, Hiroaki Yoshioka, Hiroaki Minamide, Yuji Oki, Chihaya Adachi, Fluorescence lifetime elongation of thermally activated delayed fluorescence 4CzIPN molecules with encapsulation into zeolitic imidazole frameworks ZIF-11, OPTICAL MATERIALS EXPRESS, 10.1364/OME.9.001150, 9, 3, 1150-1160, 2019.03, [URL], Encapsulation of fluorescent directives "thermally activated delayed fluorescence" molecules into a zeolitic imidazole frameworks was proposed, and 4CzIPN molecules were successfully encapsulated into ZIF-11 pores by one step process with a loading efficiency of 0.064 of the proportion of 4CzIPN/ZIF-11. Some Spectroscopic studies such as XRD, UV-Vis, FTIR, THz-TDS and time resolved streak measurement, and the suppression of intramolecular vibrational, rotational and librational motions of 4CzIPN molecules were confirmed. Interestingly, the florescence lifetime of 4CzIPN was considerably elongated from 2.37 ns to 14.8 ns, while the phosphorescence lifetime became a little bit short from 2.15 mu s to 1.65 mu s. The lifetime differences was thought to be due to the suppression of the 4CzIPN molecules' motion by the close ZIF-11 frameworks that affected the reverse intersystem crossing. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement. |
| 379. | Xing Li, Yi Zhong Shi, Kai Wang, Ming Zhang, Cai Jun Zheng, Dian Ming Sun, Gao Le Dai, Xiao Chun Fan, De Qi Wang, Wei Liu, Yan Qing Li, Jia Yu, Xue Mei Ou, Chihaya Adachi, Xiao Hong Zhang, Thermally Activated Delayed Fluorescence Carbonyl Derivatives for Organic Light-Emitting Diodes with Extremely Narrow Full Width at Half-Maximum, ACS Applied Materials and Interfaces, 10.1021/acsami.8b19635, 11, 14, 13472-13480, 2019.04, [URL], Two novel thermally activated delayed fluorescence (TADF) emitters, 3-phenylquinolino[3,2,1-de]acridine-5,9-dione (3-PhQAD) and 7-phenylquinolino[3,2,1-de]acridine-5,9-dione (7-PhQAD), were designed and synthesized based on a rigid quinolino[3,2,1-de]acridine-5,9-dione (QAD) framework. With the effective superimposed resonance effect from electron-deficient carbonyls and electron-rich nitrogen atom, both emitters realize significant TADF characteristics with small ΔE ST s of 0.18 and 0.19 eV, respectively. And, molecular relaxations were dramatically suppressed for both emitters because of their conjugated structure. In the devices, 3-PhQAD realizes superior performance with a maximum external quantum efficiency (EQE) of 19.1% and a narrow full width at half-maximum (FWHM) of 44 nm, whereas a maximum EQE of 18.7% and an extremely narrow FWHM of 34 nm are realized for 7-PhQAD. These superior results reveal that apart from nitrogen and boron-aromatic systems, QAD framework can also act as a TADF matrix with effective resonance effect, and QAD derivatives are ideal candidates to develop TADF emitters with narrow FWHMs for practical applications.. |
| 380. | Yanqiong Zheng, Junle Yu, Jie Tang, Fang Yang, Chao Wang, Bin Wei, Xifeng Li, Chihaya Adachi, Series of polar alcohol-additives assisted improvement in the PEDOT:PSS film property and bulk-heterojunction organic solar cell performance, Journal of Physics D: Applied Physics, 10.1088/1361-6463/ab04dc, 52, 25, 2019.04, [URL], Doping poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) by polar solvent is a promising approach to decrease the resistivity of pristine PEDOT:PSS film. In this work, properties of doped PEDOT:PSS films by a series of alcohol additives, including ethanol, glycerol, meso-erythritol, xylitol, and D-sorbitol, are comparatively studied for the first time. The absorption spectra, surface morphology, solvent contact angle, hole mobility, work function, and carrier transport properties via Hall measurement of these doped films were systematically investigated to find out the dopant dependent PEDOT:PSS film property. Then these low-resistivity PEDOT:PSS films were applied as the hole transport layer in 20 wt% poly(diketopyrro lopyrrole-terthiophene) (PDPP3T) based bulk heterojunctions (BHJs), and the highest power conversion efficiency (PCE) of 3.74% was achieved for the meso-erythritol doped PEDOT:PSS based BHJ, which is 21% higher than that (3.09%) of the pristine PEDOT:PSS based BHJ. Finally, the performance of all six BHJs is significantly improved by using lithium fluoride instead of bathocuproine, and the PCE for the meso-erythritol doped PEDOT:PSS based BHJ achieves 4.86%. Among these alcohol additives, meso-erythritol and D-sorbitol depict the optimum doping effect. Our results give important guidance to develop alcohol-additive doped PEDOT:PSS films in organic optoelectronic devices.. |
| 381. | Shin Hyung Choi, Chan Hee Lee, Chihaya Adachi, Sae Youn Lee, Molecular design of highly effective thermally activated delayed fluorescence emitters based on ortho-substituted donor-acceptor-donor pyridinecarbonitrile derivatives and their application for high-performance OLEDs, Dyes and Pigments, 10.1016/j.dyepig.2019.107775, 171, 2019.12, [URL], In this work, we designed and investigated two TADF molecules, AcCN and PxCN, introducing donor moieties into the 3,5-position of 4-pyridinecarbonitrile acceptor core. These D‒A‒D type compounds exhibit effective utilization of triplet excitons through a reverse intersystem crossing (RISC) process with relatively small singlet-triplet energy splitting (ΔEST) values less than 0.1 eV. With their high PL quantum yield (ΦPL) and sufficient rate constant for RISC process (kRISC), organic light-emitting diodes (OLEDs) employing AcCN and PxCN as emitters achieve a maximum external quantum efficiency (ηext) of 20.6% and 15.5%, respectively, with green emissions.. |
| 382. | Shin Hyung Choi, Chan Hee Lee, Chihaya Adachi, Sae Youn Lee, Highly effective nicotinonitrile-derivatives-based thermally activated delayed fluorescence emitter with asymmetric molecular architecture for high-performance organic light-emitting diodes, Dyes and Pigments, 10.1016/j.dyepig.2019.107849, 172, 2020.01, [URL], In this paper, we report a new molecular architecture for increasing the emission efficiency of nicotinonitrile-derivatives-based donor-acceptor-donor combined thermally activated delayed fluorescence (TADF) emitters with asymmetric molecular architecture. The proposed molecular design facilitates highly effective TADF emission through a relatively small singlet (S1) and triplet (T1) energy gap (ΔEST ≈ 0.1 eV) and provides an increased reverse intersystem crossing efficiency (ΦRISC) of up to 86% from T1 to S1 states. Organic light-emitting diodes (OLEDs) employing the proposed asymmetric nicotinonitrile derivatives as emitters exhibit external quantum efficiencies (ηext) of up to 18.5% in greenish-blue and green emissions.. |
| 383. | Youichi Tsuchiya, Keita Tsuji, Ko Inada, Fatima Bencheikh, Yan Geng, H. Shaun Kwak, Thomas J.L. Mustard, Mathew D. Halls, Hajime Nakanotani, Chihaya Adachi, Molecular Design Based on Donor-Weak Donor Scaffold for Blue Thermally-Activated Delayed Fluorescence Designed by Combinatorial DFT Calculations, Frontiers in Chemistry, 10.3389/fchem.2020.00403, 8, 2020.05, [URL], Quantum chemical calculations are necessary to develop advanced emitter materials showing thermally-activated delayed fluorescence (TADF) for organic light-emitting diodes (OLEDs). However, calculation costs become problematic when more accurate functionals were used, therefore it is judicious to use a multimethod approach for efficiency. Here we employed combinatorial chemistry in silico to develop the deep blue TADF materials with a new concept of homo-junction design. The homo-junction materials containing TADF candidates designed by calculation were synthesized and analyzed. We found that these materials showed the emission from charge transfer (CT) state, and the clear delayed emission was provided in solid state. Because the homo-junction TADF materials showed three exponential decayed emission in solid state, we employed novel four-state kinetic analysis.. |
| 384. | Petter Lundberg; Youichi Tsuchiya; E. Mattias Lindh; Shi Tang; Chihaya Adachi; Ludvig Edman, Thermally activated delayed fluorescence with 7% external quantum efficiency from a light-emitting electrochemical cell, Nature Communications, 10.1038/s41467-019-13289-w, 10, 5307, 2019.11. |
| 385. | Takahiko Yamanaka; Hajime Nakanotani; Chihaya Adachi, Slow recombination of spontaneously dissociated organic fluorophore excitons, Nature Communications, 10.1038/s41467-019-13736-8, 10, 5748, 2019.12, The harvesting of excitons as luminescence by organic fluorophores forms the basis of light-emitting applications. Although high photoluminescence quantum yield is essential for efficient light emission, concentration-dependent quenching of the emissive exciton is generally observed. Here we demonstrate generation and accumulation of concentration-dependent "long-lived" (i.e., over 1 h) photo-generated carriers and the successive release of their energy as electroluminescence in a solid-state film containing a polar fluorophore. While fluorophore excitons are generally believed to be stable because of their high exciton binding energies, our observations show that some of the excitons undergo spontaneous exciton dissociation in a solid-state film by spontaneous orientation polarization even without an external electric field. These results lead to the reconsideration of the meaning of "luminescence quantum yield" for the solid films containing polar organic molecules because it can differ for optical and electrical excitation.. |
| 386. | Ryota Ieuji; Kenichi Goushi; Chihaya Adachi, Triplet–triplet upconversion enhanced by spin–orbit coupling in organic light-emitting diodes, Nature Communications, 10.1038/s41467-019-13044-1, 10, 5283, 2019.11, Triplet-triplet upconversion, in which two triplet excitons are converted to one singlet exciton, is a well-known approach to exceed the limit of electroluminescence quantum efficiency in conventional fluorescence-based organic light-emitting diodes. Considering the spin multiplicity of triplet pairs, upconversion efficiency is usually limited to 20%. Although this limit can be exceeded when the energy of a triplet pair is lower than that of a second triplet excited state, such as for rubrene, it is generally difficult to engineer the energy levels of higher triplet excited states. Here, we investigate the upconversion efficiency of a series of new anthracene derivatives with different substituents. Some of these derivatives show upconversion efficiencies close to 50% even though the calculated energy levels of the second triplet excited states are lower than twice the lowest triplet energy. A possible upconversion mechanism is proposed based on the molecular structures and quantum chemical calculations.. |
| 387. | Masaki Tanaka; Hiroki Noda; Hajime Nakanotani; Chihaya Adachi, Molecular orientation of disk-shaped small molecule exhibiting thermally activated delayed fluorescence in host-guest films, Applied Physics Letters, 10.1063/1.5140210, 116, 2, 023302, 2020.01, Control of the molecular orientation in a glassy film is a crucial issue, not only for an understanding of the fundamental processes of organic amorphous film formation but also for enhancement of the performance of organic light-emitting diodes (OLEDs) by increasing their light-outcoupling efficiency. In this study, the molecular orientation in codeposited films composed of a host molecule and a disk-shaped emitter that exhibits thermally activated delayed fluorescence is investigated systematically. It is found that the orientation of the transition dipole moment (TDM) of the disk-shaped emitters is strongly dependent on the glass transition temperature and the polarization of the host molecules, and almost perfectly horizontal orientation of the TDM of the disk-shaped emitters can be realized. Our findings clarify the role of the host-guest dipole-dipole interaction in the molecular orientation, and it will enable the expansion of both the molecular design and the material combination rules for high-performance OLEDs.. |
| 388. | Sunbin Hwang; William J. Potscavage, Chihaya Adachi, Interplay among thermoelectric properties, atmospheric stability, and electronic structures in solution-deposited thin films of P(NaX[Niett]), Advanced Electronic Materials, 10.1002/aelm.201901172, 6, 3, 1901172, 2020.01. |
| 389. | Yuya Oyama; Masashi Mamada; Atul Shukla; Evan G. Moore; Shih-Chun Lo; Ebinazar B. Namdas; Chihaya Adachi, Design strategy for robust organic semiconductor laser dyes, ACS Materials Letters, 10.1021/acsmaterialslett.9b00536, 2, 2, 161-167, 2020.01. |
| 390. | Zesen Lin, Ryota Kabe, Kai Wang, Chihaya Adachi, Influence of energy gap between charge-transfer and locally excited states on organic long persistence luminescence, Nature Communications, 10.1038/s41467-019-14035-y, 2020.12. |
| 391. | Naoto Notsuka; Hajime Nakanotani; Hiroki Noda; Kenichi Goushi; Chihaya Adachi, Observation of Nonradiative Deactivation Behavior from Singlet and Triplet States of Thermally Activated Delayed Fluorescence Emitters in Solution, J. Phys. Chem. Lett., 10.1021/acs.jpclett.9b03302, 11, 2, 562-566, 2019.12, Excited states of emissive organic molecules undergo various kinds of quenching phenomena such as vibration-coupled quenching depending on their environmental conditions. Because bright singlet excitons in purely organic molecules exhibiting thermally activated delayed fluorescence (TADF) can access dark triplet excited states, photogenerated singlet excitons can decay nonradiatively through both singlet and triplet excited states. Here, we investigated nonradiative decay behavior, including internal and external exciton quenching processes, of various types of TADF materials in solution. Under air-saturated conditions, both the lowest singlet and triplet excited states of almost all of the TADF materials showed oxygen quenching. We considered the effect of oxygen quenching for both spin states to develop a method for determination of the triplet contribution to the total photoluminescence quantum yield from the transient photoluminescence profiles. Furthermore, we observed a clear energy gap law for the internal nonradiative processes.. |
| 392. | Shi-Bin Ruan; Chin-Yiu Chan; Hao Ye; Ko Inada; Fatima Bencheikh; Atula S. D. Sandanayaka; Toshinori Matsushima; Chihaya Adachi, A spirofluorene-end-capped bis-stilbene derivative with a low amplified spontaneous emission threshold and balanced hole and electron mobilities, Optical Materials, 10.1016/j.optmat.2019.109636, 100, 109636, 2020.02. |
| 393. | Zesen Lin; Ryota Kabe; Chihaya Adachi, Orange Organic Long-persistent Luminescence from an Electron Donor/Acceptor Binary System, Chemistry Letters, 10.1246/cl.190823, 49, 2, 203-206, 2019.12. |
| 394. | Kenta Yamaguchi; Toshinori Matsushima; Atula S. D. Sandanayaka; Yoko Homma; Naoki Uchida; Chihaya Adachi, Enhanced operational durability of thermally activated delayed fluorescence-based organic light-emitting diodes with a triazine electron transporter, Chemistry A European Journal, 10.1002/chem.201905345, 26, 25, 5598-5602, 2020.05. |
| 395. | Thanh Ba Nguyen; Hajime Nakanotani; Takuji Hatakeyama; Chihaya Adachi, The Role of reverse intersystem crossing using a TADF-type acceptor molecule on the device stability of exciplex based organic-light emitting diodes, Advanced Materials, 10.1002/adma.201906614, 32, 9, 1906614, 2020.01, Exciplex system exhibiting thermally activated delayed fluorescence (TADF) holds a considerable potential to improve organic light-emitting diode (OLED) performances. However, the operational lifetime of current exciplex-based devices, unfortunately, falls far behind the requirement for commercialization. Herein, rationally choosing a TADF-type electron acceptor molecule is reported as a new strategy to enhance OLEDs' operating lifetime. A comprehensive study of the exciplex system containing 9,9 ',9 ''-triphenyl-9H,9 ' H,9 '' H-3,3 ':6 ',3 ''-tercarbazole (Tris-PCz) and triazine (TRZ) derivatives clarifies the relationship between unwanted carrier recombination on acceptor molecules, TADF property of acceptors, and the device degradation event. By employing a proposed "exciton recycling" strategy, a threefold increased operational lifetime can be achieved while still maintaining high-performance OLED properties. In particular, a stable blue OLED that employs this strategy is successfully demonstrated. This research provides an important step for exciplex-based devices toward the significant improvement of operational stability.. |
| 396. | Takashi Kobayashi, Daisuke Kawate, Akitsugu Niwa, Takashi Nagase, Kenichi Goushi, Chihaya Adachi, Hiroyoshi Naito, Intersystem Crossing Rate in Thermally Activated Delayed Fluorescence Emitters, Physica Status Solidi (A) Applications and Materials Science, 10.1002/pssa.201900616, 217, 3, 2020.02, © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim For a better understanding of the exciton decay process in thermally activated delayed fluorescence (TADF) emitters, the intersystem crossing rate, kISC, is one of the important physical constants that have to be determined. Herein, a method to calculate the kISC value from photoluminescence (PL) measurements is reconsidered. The kISC value can be determined at very low temperatures where delayed fluorescence (DF) is completely suppressed, as well as around room temperature where triplet excitons mainly decay into the ground state by emitting DF. However, there is a temperature range where the kISC value cannot be determined accurately because the influences of nonradiative decay paths can be neither ignored nor corrected. For such a temperature range, an alternative approach, which utilizes the temperature dependence of an observed PL decay rate, is presented. In this way, kISC values from 300 to 10 K are determined for thin films of two TADF emitters, i.e., 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene, which are known as 4CzIPN and 2CzPN, respectively.. |
| 397. | Umamahesh Balijapalli; Masaki Tanaka; Morgan Auffray; Chin-Yiu Chan; Yi-Ting Lee; Youichi Tsuchiya; Hajime Nakanotani; Chihaya Adachi, Utilization of multi hetero-donors in thermally activated delayed fluorescence molecules and their high performance bluish-green OLEDs, ACS Appl. Mater. Interfaces, 10.1021/acsami.9b20020, 12, 8, 9498-9506, 2020.02. |
| 398. | Ganbaatar Tumen-Ulzii; Chuanjiang Qin; Dino Klotz; Matthew R. Leyden ; Pangpang Wang; Morgan Auffray; Takashi Fujihara; Toshinori Matsushima; Jin-Wook Lee; Sung-Joon Lee; Yang Yang; Chihaya Adachi, Detrimental Effect of Unreacted PbI2 on the Long-Term Stability of Perovskite Solar Cells, Advanced Materials, 10.1002/adma.201905035, 1905035, 2020.04. |
| 399. | Masaki Tanaka; Ryo Nagata; Hajime Nakanotani; Chihaya Adachi, Understanding degradation of organic lightemitting diodes from magnetic field effects, Communication Materials, 10.1038/s43246-020-0019-0, 1, 1, 18, 2020.04. |
| 400. | Hiroshi Fujimoto; Toshimitsu Nakamura; Kaori Nagayoshi; Kentaro Harada; Hiroshi Miyazaki; Takaomi Kurata; Junya Kiyota; Chihaya Adachi, Killer Impurities in Vacuum Chamber that Affect the Lifetime of Organic Light-Emitting Diodes, Applied Physics Letters, 10.1063/1.5141101, 116, 143301, 2020.04. |
| 401. | Naohiro Nishimura; Zesen Lin; Kazuya Jinnai; Ryota Kabe; Chihaya Adachi, Many exciplex systems exhibit organic long-persistent luminescence, Advanced Functional Materials, 10.1002/adfm.202000795, 30, 22, 2000795, 2020.04. |
| 402. | Jong Uk Kim; In Seob Park; Chin-Yiu Chan; Masaki Tanaka; Youichi Tsuchiya; Hajime Nakanotani; Chihaya Adachi, Nanosecond-Time-Scale Delayed Fluorescence Molecule for Deep-Blue OLEDs with Small Efficiency Rolloff, Nature Communications, 10.1038/s41467-020-15558-5, 11, 1965, 2020.04. |
| 403. | Tai Cheng; Chuanjiang Qin; Satoru Watanabe; Toshinori Matsushima; Chihaya Adachi, Stoichiometry control for the tuning of grain passivation and domain distribution in green quasi-2D metal halide perovskite films and light-emitting diodes, Advanced Functional Materials, 10.1002/adfm.202001816, 30, 24, 2001816, 2020.04. |
| 404. | Yun Long; Masashi Mamada; Chunyong Li; Paloma Lays dos Santos; Marco Colella; Andrew Danos; Chihaya Adachi; Andrew Monkman, Excited State Dynamics of Thermally Activated Delayed Fluorescence from an Excited State Intramolecular Proton Transfer System, The Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.0c00498, 11, 9, 3305-3312, 2020.04. |
| 405. | Monirul Hasan; Atul Shukla; Viqar Ahmad; Jan Sobus; Fatima Bencheikh; Sarah M. K. McGregor; Masashi Mamada; Chihaya Adachi ; Shih-Chun Lo; Ebinazar B. Namdas, Exciton-exciton annihilation in thermally activated delayed fluorescence emitter, Advanced Functional Materials, 10.1002/adfm.202000580, 2000580, 2020.06. |
| 406. | Masashi Mamada; Ryutaro Komatsu; Chihaya Adachi, F8BT Oligomers for Organic Solid-State Lasers, ACS Appl. Mater. Interfaces, 10.1021/acsami.0c05449, 12, 25, 28383-28391, 2020.05. |
| 407. | Ganbaatar Tumen-Ulzii; Toshinori Matsushima; Dino Klotz; Matthew R. Leyden; Pangpang Wang; Chuanjiang Qin; Jin-Wook Lee; Sung-Joon Lee; Yang Yang; Chihaya Adachi, Hysteresis-less and stable perovskite solar cells with a self-assembled monolayer, Communications Materials, 10.1038/s43246-020-0028-z, 1, 31, 2020.05. |
| 408. | Kenta Yamaguchi; Toshinori Matsushima; Chihaya Adachi, A 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) transport layer with high electron mobility for thick organic light-emitting diodes, AIP Advances, 10.1063/5.0007310, 10, 055304, 2020.05. |
| 409. | Buddhika S. B. Karunathilaka; Umamahesh Balijapalli; Chathuranganie A. M. Senevirathne; Yu Esaki; Toshinori Matsushima; Atula S. D. Sandanayaka; Chihaya Adachi, An organic laser dye having a small singlet-triplet energy gap makes the selection of a host material easier, Advanced Functional Materials, 10.1002/adfm.202001078, 30, 30, 2001078, 2020.06, Quenching of singlets by long-lived triplets is a serious issue for lasing from organic laser dyes, especially under long pulse excitation. As a strategy to scavenge or manage unnecessary triplets, an organic laser dye is dispersed into a host material having high singlet and low triplet energy levels [a large singlet-triplet energy gap (Delta E-ST)]. However, finding such a host material having a triplet scavenging capability is limited. In this study, an organic laser dye, 2,6-dicyano-1,1-diphenyl-lambda(5)sigma(4)-phosphinine (DCNP), having a small Delta E-ST of approximate to 0.44 eV is synthesized, and thus 4-4 '-bis[(N-carbazole)styryl] biphenyl (BSBCz) can be employed as a triplet scavenging host, i.e., the triplets formed on DCNP are easily transferred to BSBCz. A 1 wt%-DCNP-doped BSBCz film is formed on a mixed-order distributed feedback grating, showing lasing with a low threshold value of approximate to 0.86 mu J cm(-2) and a full-width-at-half-maximum value of approximate to 0.5 nm. Because of the suppressed singlet-triplet annihilation, DCNP-based laser devices operating under a continuous-wave regime, with a low threshold of 72 W cm(-2) and a long laser half-lifetime of approximate to 3 min, are demonstrated. These results indicate a possibility of the wider selection of host materials, easing a material design strategy of fabricating high-performance laser devices in future.. |
| 410. | Viqar Ahmad; Jan Sobus; Fatima Bencheikh; Masashi Mamada; Chihaya Adachi ; Shih-Chun Lo; Ebinazar B. Namdas, High EQE and high brightness solution-processed TADF light-emitting transistors and OLEDs, Viqar Ahmad; Jan Sobus; Fatima Bencheikh; Masashi Mamada; Chihaya Adachi ; Shih-Chun Lo; Ebinazar B. Namdas, 10.1002/adom.202000554, 8, 11, 2000554, 2020.07. |
| 411. | Paulius Baronas; Gediminas Kreiza; Masashi Mamada; Satoshi Maedera; Povilas Adomėnas; Ona Adomėnienė; Karolis Kazlauskas; Chihaya Adachi; Saulius Juršėnas, Enhanced Energy Transfer in Doped Bifluorene Single Crystals: Prospects for Organic Lasers, Advanced Optical Materials, 10.1002/adom.201901670, 1901670, 2019.12. |
| 412. | Ya-Kun Wang; Chen-Chao Huang; Hao Ye; Cheng Zhong; Aziz Khan; Sheng-Yi Yang; Man-Keung Fung; Zuo-Quan Jiang; Chihaya Adachi; Liang-Sheng Liao, Through Space Charge Transfer for Efficient Sky-Blue Thermally Activated Delayed Fluorescence (TADF) Emitter with Unconjugated Connection, Advanced Optical Materials, 10.1002/adom.201901150, 1901150, 2019.11. |
| 413. | Satoru Watanabe; Tai Cheng; Ganbaatar Tumen-Ulzii; Chuanjiang Qin; Toshinori Matsushima; Chihaya Adachi, Excited-state stability of quasi-two-dimensional metal halide perovskite films under optical and electrical excitations, Applied Physics Letters, 10.1063/1.5127308, 115, 23, 233502, 2019.11. |
| 414. | Fatima Bencheikh; Atula S. D. Sandanayaka; Toshiya Fukunaga; Toshinori Matsushima; Chinaya Adachi, Origin of external quantum efficiency roll-off in 4,4′-bis[(N-carbazole)styryl]biphenyl (BSBCz)-based inverted organic light emitting diode under high pulsed electrical excitation, Journal of Applied Physics, 10.1063/1.5121485, 126, 18, 185501, 2019.11. |
| 415. | Chuanjiang Qin, Toshinori Matsushima, William J. Potscavage, Atula S. D. Sandanayaka, Matthew R. Leyden, Fatima Bencheikh, Kenichi Goushi, Fabrice Mathevet, Benoit Heinrich, Go Yumoto, Yoshihiko Kanemitsu, Chihaya Adachi, Triplet management for efficient perovskite light-emitting diodes, NATURE PHOTONICS, 10.1038/s41566-019-0545-9, 14, 2, 70-+, 2020.02, Careful harvesting of triplet excitons allows the realization of efficient green-emitting quasi-2D perovskite LEDs.Perovskite light-emitting diodes are promising for next-generation lighting and displays because of their high colour purity and performance(1). Although the management of singlet and triplet excitons is fundamental to the design of efficient organic light-emitting diodes, the nature of how excitons affect performance is still not clear in perovskite(2-4) and quasi-two-dimensional (2D) perovskite-based devices(5-9). Here, we show that triplet excitons are key to efficient emission in green quasi-2D perovskite devices and that quenching of triplets by the organic cation is a major loss path. Employing an organic cation with a high triplet energy level (phenylethylammonium) in a quasi-2D perovskite based on formamidinium lead bromide yields efficient harvesting of triplets. Furthermore, we show that upconversion of triplets to singlets can occur, making 100% harvesting of electrically generated excitons potentially possible. The external quantum and current efficiencies of our green (527 nm) devices reached 12.4% and 52.1 cd A(-1), respectively.. |
| 416. | Dino Klotz; Ganbaatar Tumen-Ulzii; Chuanjiang Qin; Toshinori Matsushima; Chihaya Adachi, Detecting and identifying reversible changes in perovskite solar cells by electrochemical impedance spectroscopy, RSC Advances, 10.1039/C9RA07048F, 9, 33436-33445, 2019.10. |
| 417. | Jia-Xiong Chen; Wen-Wen Tao; Wen-Cheng Chen; Ya-Fang Xiao; Kai Wang; Chen Cao ; Jia Yu; Shengliang Li; Feng-Xia Geng; Chihaya Adachi; Chun-Sing Lee; Xiao-Hong Zhang, Red/Near-Infrared Thermally Activated Delayed Fluorescence OLEDs with Near 100% Internal Quantum Efficiency, Angewandte Chemie International Edition, 10.1002/anie.201906575, 58, 41, 14660-14665, 2019.06. |
| 418. | Hosokai Takuya; Nakanotani Hajime; Santou S.; Noda Hiroki ; Nakayama Yasuo; Adachi Chihaya, TADF activation by solvent freezing: The role of nonradiative triplet decayand spin-orbit coupling in carbazole benzonitrile derivatives, Synthetic Metals, 10.1016/j.synthmet.2019.04.005, 252, 62-68, 2019.06, © 2019 Elsevier B.V. Thermally activated delayed fluorescence (TADF) materials have attracted considerable attentions as a new kind of emitters in organic light-emitting diodes. While it is requisite to minimize an energy difference between the lowest excited triplet state (T 1 ) and lowest excited singlet state (S 1 ), so-called ΔE ST , a deeper understanding of the emission mechanism is desirable to clarify the comprehensive molecular design. In this paper, we present that the TADF ability and efficiency of (rare-)metal free organic molecules are surely influenced by both the nonradiative decay of T 1 and spin-orbit coupling. By investigating a temperature dependent photoluminescence of carbazole benzonitrile derivatives in toluene solutions using a newly developed liquid nitrogen cryostat, we demonstrate the activation of TADF by solvent freezing for room temperature-TADF inactive molecules. Transient photoluminescence measurements of the frozen samples show a significant increase of a lifetime of T 1 , probing the suppression of nonradiative decay path of T 1 . A magnitude of the TADF activation by the solvent freezing is closely related to the degree of spin-orbit coupling of the molecules. The present results emphasize the importance of suppression of nonradiative decay of T 1 and an increase of spin-orbit coupling together with reducing ΔE ST to achieve a high TADF emission efficiency.. |
| 419. | Xian-Kai Chen; Brandon W. Bakr; Morgan Auffray; Youichi Tsuchiya; C. David Sherrill; Chihaya Adachi; Jean-Luc Bredas, Intramolecular Noncovalent Interactions Facilitate Thermally Activated Delayed Fluorescence (TADF), The Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.9b01220, 10, 12, 3260-3268, 2019.05. |
| 420. | Rokas Skiasgiris; Tomas Serevisius; Karolis Kazlauskas; Yan Geng; Chihaya Adachi; Saulius Jursenas, Origin of dual emission in σ-bridged donor–acceptor TADF compounds, Journal of Materials Chemistry C, 10.1039/C9TC03548F, 7, 12601-12609, 2019.09. |
| 421. | Matthew R. Leyden; Toshinori Matsushima; Fatima Bencheikh; Chihaya Adachi, Film Transfer of Structured Organo-Lead-Halide Perovskite for Low-Cost Lasing Applications, Applied Physics Letters, 10.1063/1.5113647, 115, 14, 141106, 2019.10. |
| 422. | Hiroki Noda; Xian-Kai Chen; Hajime Nakanotani; Takuya Hosokai; Momoka Miyajima; Naoto Noutsuka; Yuuki Kashima; Jean-Luc Bredas; Chihaya Adachi, Critical role of intermediate electronic states for spin-flip processes in charge-transfer-type organic molecules with multiple donors and acceptors, Nature Materials, 10.1038/s41563-019-0465-6, 18, 10, 1084-1090, 2019.09, Spin-flip in purely organic molecular systems is often described as a forbidden process; however, it is commonly observed and utilized to harvest triplet excitons in a wide variety of organic material-based applications. Although the initial and final electronic states of spin-flip between the lowest singlet and lowest triplet excited state are self-evident, the exact process and the role of intermediate states through which spin-flip occurs are still far from being comprehensively determined. Here, via experimental photo-physical investigations in solution combined with first-principles quantum-mechanical calculations, we show that efficient spin-flip in multiple donor-acceptor charge-transfer-type organic molecular systems involves the critical role of an intermediate triplet excited state that corresponds to a partial molecular structure of the system. Our proposed mechanism unifies the understanding of the intersystem crossing mechanism in a wide variety of charge-transfer-type molecular systems, opening the way to greater control over spin-flip rates.. |
| 423. | Gang-Yuan Li; Hao Ye; Fu-Cheng Zhu; Yan Geng; Jian-Zhong Fan; Jian-Ping Ma; Chihaya Adachi; Yu-Bin Dong, Luminescent Cu(I) and Ag(I) Coordination Polymers: Fast Phosphorescence or Thermally Activated Delayed Fluorescence, Chinese Chemical Letters, 10.1016/j.cclet.2019.08.006, 30, 11, 1931-1934, 2019.09. |
| 424. | Patrik Ščajev; Ramunas Aleksiejunas; Paulius Baronas; Džiugas Litvinas; Marek Kolenda; Chuanjiang Qin; Takashi Fujihara; Toshinori Matsushima; Chihaya Adachi; Saulius Juršėnas, Carrier Recombination and Diffusion in Wet-Cast Tin Iodide Perovskite Layers Under High Intensity Photoexcitation, J. Phys. Chem. C, 10.1021/acs.jpcc.9b03226, 123, 32, 19275-19281, 2019.07. |
| 425. | Toshinori Matsushima; Matthew R. Leyden; Takashi Fujihara; Chuanjiang Qin; Atula S. D. Sandanayaka; Chihaya Adachi, Large metal halide perovskite crystals for field-effect transistor applications, Applied Physics Letters, 10.1063/1.5116411, 115, 120601, 2019.09. |
| 426. | Toshinori Matsushima; Fatima Bencheikh; Takeshi Komino; Matthew R. Leyden; Atula S. D. Sandanayaka; Chuanjiang Qin; Chihaya Adachi, High performance from extraordinarily thick organic light-emitting diodes, Nature, 10.1038/s41586-019-1435-5, 572, 502-506, 2019.07. |
| 427. | Jong Uk Kim; Michael Y. Wong; Shiv Kumar; Oliver G. Hayes; Finlay Duncan; Chin-Yiu Chan; Ben Yiu-Wing Wong; Hao Ye; Lin-Song Cui; Hajime Nakanotani; Eli Zysman-Colman; Chihaya Adachi, High-Triplet-Energy Bipolar Host Materials Based on Phosphine Oxide Derivatives for Efficient Sky-Blue Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes with Reduced Roll-off, Chemistry Letters, 10.1246/cl.190412, 48, 10, 1225-1228, 2019.09. |
| 428. | Patrik Scajev; Ramunas Aleksiejunas; Shinobu Terakawa; Chuanjiang Qin; Takashi Fujihara; Toshinori Matsushima; Chihaya Adachi; Saulius Jursenas, Anisotropy of Thermal Diffusivity in Lead Halide Perovskite Layers Revealed by Thermal Grating Technique, The Journal of Physical Chemistry C, 10.1021/acs.jpcc.9b02288, 123, 24, 14914-14920, 2019.05. |
| 429. | Toshinori Matsushima; Shinobu Terakawa; Matthew R. Leyden; Takashi Fujihara; Chuanjiang Qin; Chihaya Adachi, Toward air-stable field-effect transistors with a tin iodide-based hybrid perovskite semiconductor, Journal of Applied Physics, 10.1063/1.5097433, 125, 235501, 2019.06. |
| 430. | Atula S. D. Sandanayaka; Toshinori Matsushima ; Fatima Bencheikh; Shinobu Terakawa; William J. Potscavage Jr.; Chuanjiang Qin; Takashi Fujihara; Kenichi Goushi; Jean-Charles Ribierre; Chihaya Adachi, Indication of current-injection lasing from an organic semiconductor, Applied Physics Express, 10.7567/1882-0786/ab1b90, 12, 6, 061010, 2019.05, In this study, we investigate the lasing properties of 4,4'-bis[(N-carbazole) styryl] biphenyl thin films under electrical pumping. The electroluminescent devices incorporate a mixed-order distributed feedback SiO2 grating into an organic light-emitting diode structure and emit blue lasing. The results provide an indication of lasing by direct injection of current into an organic thin film through selection of a high-gain organic semiconductor showing clear separation of the lasing wavelength from significant triplet and polaron absorption and design of a proper feedback structure with low losses at high current densities. This study represents an important advance toward a future organic laser diode technology. (C) 2019 The Japan Society of Applied Physics. |
| 431. | Nidhi Sharma; Eduard Spuling; Cornelia M. Mattern; Wenbo Li; Olaf Fuhr; Youichi Tsuchiya; Chihaya Adachi; tefan Bräse; Ifor D. W. Samuel; Eli Zysman-Colman, Turn on of Sky-Blue Thermally Activated Delayed Fluorescence and Circularly Polarized Luminescence (CPL) via Increased Torsion by a Bulky Carbazolophane Donor, Chemical Science, 10.1039/C9SC01821B, 10, 6689-6696, 2019.05. |
| 432. | Yu Esaki; Toshinori Matsushima; Chihaya Adachi, Discussion on hole traps of amorphous films of N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (α-NPD) deposited at different substrate temperatures, Applied Physics Letters, 10.1063/1.5089269, 114, 173301, 2019.05. |
| 433. | Morgan Auffray; Dae Hyeon Kim; Jong Uk Kim; Fatima Bencheikh; David Kreher; Qisheng Zhang ; Anthony D’Aléo; Jean-Charles Ribierre; Fabrice Mathevet; Chihaya Adachi, Dithia[3.3]paracyclophane Core: a Versatile Platform for Fine Triplet State Tuning and Through Space TADF Emission, Chemistry - An Asian Journal, 10.1002/asia.201900401, 14, 11, 1921-1925, 2019.05. |
| 434. | Saigo Masaki, Miyata Kiyoshi, Tanaka Sei'ichi, Nakanotani Hajime, Adachi Chihaya, Onda Ken, Suppression of Structural Change upon S-1-T-1 Conversion Assists the Thermally Activated Delayed Fluorescence Process in Carbazole-Benzonitrile Derivatives, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 10.1021/acs.jpclett.9b00810, 10, 10, 2475-2480, 2019.05. |
| 435. | Brett Yurash; Hajime Nakanotani; Yoann Olivier; David Beljonne; Chihaya Adachi ; Thuc‐Quyen Nguyen, Photoluminescence Quenching Probes Spin Conversion and Exciton Dynamics in Thermally Activated Delayed Fluorescence Materials, Advanced Materials, 10.1002/adma.201804490, 31, 21, 1804490, 2019.05, Fluorescent materials that efficiently convert triplet excitons into singlets through reverse intersystem crossing (RISC) rival the efficiencies of phosphorescent state-of-the-art organic light-emitting diodes. This upconversion process, a phenomenon known as thermally activated delayed fluorescence (TADF), is dictated by the rate of RISC, a material-dependent property that is challenging to determine experimentally. In this work, a new analytical model is developed which unambiguously determines the magnitude of RISC, as well as several other important photophysical parameters such as exciton diffusion coefficients and lengths, all from straightforward time-resolved photoluminescence measurements. From a detailed investigation of five TADF materials, important structure-property relationships are derived and a brominated derivative of 2,4,5,6-tetrakis(carbazol-9-yl)isophthalonitrile that has an exciton diffusion length of over 40 nm and whose excitons interconvert between the singlet and triplet states approximate to 36 times during one lifetime is identified.. |
| 436. | Toshinori Matsushima; Chuanjiang Qin; Kenichi Goushi; Fatima Bencheikh; Takeshi Komino; Matthew Leyden; Atula S. D. Sandanayaka; Chihaya Adachi, Enhanced Electroluminescence from Organic Light-Emitting Diodes with an Organic-Inorganic Perovskite Host Layer, Advanced Materials, 10.1002/adma.201802662, 30, 38, 1802662, 2018.08, The development of host materials with high performance is essential for fabrication of efficient and stable organic light-emitting diodes (OLEDs). Although host materials used in OLEDs are typically organics, in this study, it is shown that the organic-inorganic perovskite CH3NH3PbCl3 (MAPbCl(3)) can be used as a host layer for OLEDs. Vacuum-evaporated MAPbCl(3) films have a wide band gap of about 3 eV and very high and relatively balanced hole and electron mobilities, which are suitable for the host material. Photoluminescence and electroluminescence take place through energy transfer from MAPbCl(3) to an organic emitter in films. Incorporation of an MAPbCl(3) host layer into OLEDs leads to a reduction of driving voltage and enhancement of external quantum efficiency as compared to devices with a conventional organic host layer. Additionally, OLEDs with an MAPbCl(3) host layer demonstrate very good operational stability under continuous current operation. These results can be extensively applied to organic- and perovskite-based optoelectronics.. |
| 437. | Fujimoto Hiroshi, Kobayashi Shin-ichiro, Mo Hin Wai, Yukiwaki Satoshi, Nagayoshi Kaori, Yasumatsu Mao, Harada Kentaro, Adachi Chihaya, Vacuum chamber considerations for improved organic light-emitting diode lifetime, AIP ADVANCES, 10.1063/1.5047542, 8, 8, 2018.08. |
| 438. | Chuanjiang Qin; Toshinori Matsushima; Dino Klotz; Takashi Fujihara; Chihaya Adachi, The relation of phase transition effects and thermal stability of planar perovskite solar cells, Advanced Science, 10.1002/advs.201801079, 6, 1, 1801079, 2018.10. |
| 439. | Hao Ye; Dae Hyeon Kim; Xiankai Chen; Atula S. D. Sandanayaka; Jong Uk Kim; Elena Zaborova; Gabriel Canard; Youichi Tsuchiya; Eun Young Choi; Jeong Weon Wu; Fr?d?ric Fages; Jean-Luc Bredas; Anthony D’Al?o; Jean-Charles Ribierre; Chihaya Adachi, Near-Infrared Electroluminescence and Low Threshold Amplified Spontaneous Emission above 800 nm from a Thermally Activated Delayed Fluorescent Emitter, Chemistry of Materials, 10.1021/acs.chemmater.8b02247, 30, 19, 6702-6710, 2018.08. |
| 440. | Van T, N. Mai, Atul Shukla, Masashi Mamada, Satoshi Maedera, Paul E. Shaw, Jan Sobus, Ilene Allison, Chihaya Adachi, Ebinazar B. Namdas, Shih-Chun Lo, Low ASE Threshold and Efficient Electroluminescence from a Carbazole Derivatized Excited State Intramolecular Proton Transfer (ESIPT) Dye, ACS Photonics, 10.1021/acsphotonics.8b00907, 2018.10. |
| 441. | Kara Kearney; Gabseok Seo; Toshinori Matsushima; Chihaya Adachi; Elif Ert; Angus Rockett, Computational Analysis of the Interplay between Deep Level Traps and Perovskite Solar Cell Efficiency, Journal of the American Chemical Society, 10.1021/jacs.8b06002, 140, 46, 15655-15660, 2018.10. |
| 442. | Chin-Yiu Chan; Masaki Tanaka; Hajime Nakanotani; Chihaya Adachi, Efficient and stable sky-blue delayed fluorescence organic light-emitting diodes with CIEy below 0.4, Nature Communications, 10.1038/s41467-018-07482-6, 9, 5036, 2018.11. |
| 443. | Hiroki Noda ; Hajime Nakanotani; Chihaya Adachi, Highly Efficient Thermally Activated Delayed Fluorescence with Slow Reverse Intersystem Crossing, Chemistry Letters, 10.1246/cl.180813, 48, 2, 126-129, 2018.11, We report an efficient luminescent molecule exhibiting thermally activated delayed fluorescence with a long-delayed fluorescence lifetime of 0.8 ms. Although the reverse intersystem crossing rate constant is small at 2.1 x 10(3) s(-1), the molecule shows a high photoluminescence quantum yield of 89 +/- 2%, indicating the suppression of nonradiative decay from the triplet state.. |
| 444. | Matthew R. Leyden; Shinobu Terakawa; Toshinori Matsushima; Shibin Ruan; Kenichi Goushi; Morgan Auffray; Atula S. D. Sandanayaka; Chuanjiang Qin; Fatima Bencheikh; Chihaya Adachi, Distributed Feedback Lasers and Light-Emitting Diodes Using 1-Naphthylmethylamnonium Low-Dimensional Perovskite, ACS Photonics, 10.1021/acsphotonics.8b01413, 6, 2, 460-466, 2019.01, This work investigates the feasibility of using low-dimensional perovskites for electrically driven lasers given the current status of perovskite light-emitting diodes and optically pumped lasers. In our progress toward electrically driven lasers, we performed a variety of measurements on bulk and low-dimensional perovskite films to give a baseline for expectations. This included the measurement of amplified spontaneous emission, lasing, and near-infrared light-emitting diodes operated at low and high current density. We considered power density thresholds needed for amplified spontaneous emission and lasing and compared this to light-emitting diodes operated at high current density to speculate on the future of electrically driven perovskite lasers. We concluded that our current perovskite devices will need current densities of similar to 4 to 10 kA/cm(2) to achieve lasing. Future devices will most significantly benefit from architectures that accommodate higher current, but meaningful reductions in threshold may also come from improved film quality and confinement.. |
| 445. | Toshinori Matsushima; Seiya Yoshida; Ko Inada; Yu Esaki; Toshiya Fukunaga; Hiroyuki Mieno; Nozomi Nakamura; Fatima Bencheikh; Matthew R. Leyden; Ryutaro Komatsu; Chuanjiang Qin; Atula S. D. Sandanayaka; Chihaya Adachi, Degradation Mechanism and Stability Improvement Strategy for an Organic Laser Gain Material 4,4′-Bis[(N-carbazole)styryl]biphenyl (BSBCz), Advanced Functional Materials, 10.1002/adfm.201807148, 29, 10, 1807148, 2019.01, Abstract The organic material 4,4′‐bis[(N‐carbazole)styryl]biphenyl (BSBCz) is an excellent gain medium for laser devices. However, BSBCz laser output quickly degrades during photoexcitation, which is an issue that must be overcome before it can be used for practical applications. In this study, the photodegradation mechanisms of BSBCz are investigated with the aim of enhancing its excited‐state stability. The photodegradation of BSBCz is attributed to instability of the triplet excited states that would occasionally decompose into other species. This decomposition reduces absorption and introduces exciton quenchers. Incorporating the triplet managing material 9,10‐di(naphtha‐2‐yl)anthracene (ADN) into BSBCz films greatly improves photoluminescence and amplified spontaneous emission stability because of the effective removal of the unstable triplets by ADN. This triplet managing method makes it possible to increase operational stability for BSBCz‐based organic light‐emitting diodes. Therefore, these results will contribute toward the fabrication of stable optically and electrically pumped organic laser diodes.. |
| 446. | Yu Esaki ; Toshinori Matsushima; Chihaya Adachi, Dependence of the amorphous structures and photoluminescence properties of tris(8-hydroxyquinolinato)aluminum films on vacuum deposition conditions, Organic Electronics, 10.1016/j.orgel.2019.01.032, 67, 237-241, 2019.01. |
| 447. | Masaki Tanaka; Hiroki Noda; Hajime Nakanotani; Chihaya Adachi, Effect of Carrier Balance on Device Degradation of Organic Light-Emitting Diodes based on Thermally Activated Delayed Fluorescence Emitters, Advanced Electronic Materials, 10.1002/aelm.201800708, 5, 5, 1800708, 2019.02, © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The relatively short device lifetime of blue organic light-emitting diodes (OLEDs) when compared with the lifetimes of green and red OLEDs is one of the crucial problems that must be overcome to enable practical application of these devices to full-color OLED displays. This work focuses on the degradation phenomena of OLEDs that are based on sky-blue thermally activated delayed fluorescence emitters and clarifies the degradation mechanisms based on spectral change of the electroluminescence, which indicates the formation of electromer emission from an electron transport layer. Additionally, it is determined that the change in the carrier balance that occurs during this degradation process can be ascribed to the formation of electron traps.. |
| 448. | Amir Mikaeili; Toshinori Matsushima; Yu Esaki; Sahar Alasvand Yazdani; Chihaya Adachi; Ezeddin Mohajerani, The origin of changes in electrical properties of organic films fabricated at various vacuum-deposition rates, Optical Materials, 10.1016/j.optmat.2019.03.012, 91, 93-100, 2019.03. |
| 449. | Sasabe,H, Sato,R, Suzuki,K, Watanabe,Y, Adachi C, Kaji, H, Kido,J, 【2018-9】Ultrahigh Power Efficiency Thermally Activated Delayed Fluorescent OLEDs by the Strategic Use of Electron‐Transport Materials, 10.1002/adom.201800376, 6, 17, 1800376, 2018.09. |
| 450. | Osada K, Goushi K, Kaji H, Adachi C, Ishii H, Noguchi Y, 2018-5】Observation of Spontaneous Orientation Polarization in Evaporated Films of Organic Light-Emitting Diode Materials, 10.1016/j.orgel.2018.04.026, 58, 313-317, 2018.04. |
| 451. | Patrik Ščajev, Chuanjiang Qin, Ramunas Aleksiejunas, Paulius Baronas, Saulius Miasojedovas, Takashi Fujihara, Toshinori Matsushima, Chihaya Adachi, Saulius Juršėnas, Diffusion Enhancement in Highly Excited MAPbI3 Perovskite Layers with Additives, Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.8b01155, 9, 12, 3167-3172, 2018.06, Carrier mobility is one of the crucial parameters determining the electronic device performance. We apply the light-induced transient grating technique to measure independently the carrier diffusion coefficient and lifetime, and to reveal the impact of additives on carrier transport properties in wet-cast CH3NH3PbI3 (MAPbI3) perovskite films. We use the high excitation regime, where diffusion length of carriers is controlled purely by carrier diffusion and not by the lifetime. We demonstrate a four-fold increase in diffusion coefficient due to the reduction of localization center density by additives however, the density dependence analysis shows the dominance of localization-limited diffusion regime. The presented approach allows us to estimate the limits of technological improvement - carrier diffusion coefficient in wet-cast layers can be expected to be enhanced by up to one order of magnitude.. |
| 452. | Mamada Masashi, Fukunaga Toshiya, Bencheikh Fatima, Sandanayaka Atula S. D, Adachi Chihaya, Low Amplified Spontaneous Emission Threshold from Organic Dyes Based on Bis-stilbene, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.201802130, 28, 32, 2018.08. |
| 453. | Toshinori Matsushima; Chuanjiang Qin; Kenichi Goushi; Fatima Bencheikh; Takeshi Komino; Matthew Leyden; Atula S. D. Sandanayaka; Chihaya Adachi, Enhanced Electroluminescence from Organic Light-Emitting Diodes with an Organic-Inorganic Perovskite Host Layer, Advanced Materials, 10.1002/adma.201802662, 30, 38, 1802662, 2018.08, The development of host materials with high performance is essential for fabrication of efficient and stable organic light-emitting diodes (OLEDs). Although host materials used in OLEDs are typically organics, in this study, it is shown that the organic-inorganic perovskite CH3NH3PbCl3 (MAPbCl(3)) can be used as a host layer for OLEDs. Vacuum-evaporated MAPbCl(3) films have a wide band gap of about 3 eV and very high and relatively balanced hole and electron mobilities, which are suitable for the host material. Photoluminescence and electroluminescence take place through energy transfer from MAPbCl(3) to an organic emitter in films. Incorporation of an MAPbCl(3) host layer into OLEDs leads to a reduction of driving voltage and enhancement of external quantum efficiency as compared to devices with a conventional organic host layer. Additionally, OLEDs with an MAPbCl(3) host layer demonstrate very good operational stability under continuous current operation. These results can be extensively applied to organic- and perovskite-based optoelectronics.. |
| 454. | Kazuya Jinnai, Ryota Kabe, Chihaya Adachi, Wide-Range Tuning and Enhancement of Organic Long-Persistent Luminescence Using Emitter Dopants, Advanced Materials, 10.1002/adma.201800365, 1800365, 2018.09. |
| 455. | Mamada M, Tian G, Nakanotani H, Su J, Adachi C, The Importance of Excited-State Energy Alignment for Efficient Exciplex Systems Based on a Study of Phenylpyridinato Boron Derivatives., Angewandte Chemie (International ed. in English), 10.1002/anie.201804218, 2018.07. |
| 456. | Akitsugu Niwa, Shota Haseyama, Takashi Kobayashi, Takashi Nagase, Kenichi Goushi, Chihaya Adachi, Hiroyoshi Naito, Triplet-triplet annihilation in a thermally activated delayed fluorescence emitter lightly doped in a host, Applied Physics Letters, 10.1063/1.5025870, 113, 8, 083301, 2018.08, © 2018 Author(s). Triplet-triplet annihilation (TTA) will change the ratio between fluorescence and phosphorescence in the photoluminescence spectrum of a thermally activated delayed fluorescence emitter at very low temperature. Using the resultant spectral blueshift, this study investigated the nature of TTA in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) doped in a host material. The spectral blueshift is not caused by singlet-triplet annihilation and the emitter saturation effect and is less influenced by the emitter aggregates, particularly for the case of a lower doping concentration. Using these features, it is possible to focus on TTA. For 4CzIPN, the spectral blueshift due to TTA is recognized even in samples with the doping concentration as low as 1 wt. %.. |
| 457. | Chuanjiang Qin; Toshinori Matsushima; Dino Klotz; Takashi Fujihara; Chihaya Adachi, The relation of phase transition effects and thermal stability of planar perovskite solar cells, Advanced Science, 10.1002/advs.201801079, 6, 1, 1801079, 2018.10. |
| 458. | Zesen Lin, Ryota Kabe, Naohiro Nishimura, Kazuya Jinnai, Chihaya Adachi, Organic Long-Persistent Luminescence from a Flexible and Transparent Doped Polymer, Advanced Materials, 10.1002/adma.201803713, 1803713, 2018.09. |
| 459. | Hao Ye; Dae Hyeon Kim; Xiankai Chen; Atula S. D. Sandanayaka; Jong Uk Kim; Elena Zaborova; Gabriel Canard; Youichi Tsuchiya; Eun Young Choi; Jeong Weon Wu; Fr?d?ric Fages; Jean-Luc Bredas; Anthony D’Al?o; Jean-Charles Ribierre; Chihaya Adachi, Near-Infrared Electroluminescence and Low Threshold Amplified Spontaneous Emission above 800 nm from a Thermally Activated Delayed Fluorescent Emitter, Chemistry of Materials, 10.1021/acs.chemmater.8b02247, 30, 19, 6702-6710, 2018.08. |
| 460. | Kara Kearney; Gabseok Seo; Toshinori Matsushima; Chihaya Adachi; Elif Ert; Angus Rockett, Computational Analysis of the Interplay between Deep Level Traps and Perovskite Solar Cell Efficiency, Journal of the American Chemical Society, 10.1021/jacs.8b06002, 140, 46, 15655-15660, 2018.10. |
| 461. | Chin-Yiu Chan; Masaki Tanaka; Hajime Nakanotani; Chihaya Adachi, Efficient and stable sky-blue delayed fluorescence organic light-emitting diodes with CIEy below 0.4, Nature Communications, 10.1038/s41467-018-07482-6, 9, 5036, 2018.11. |
| 462. | Ribierre Jean-Charles, Li Zhao, Liu Xiao, Lacaze Emmanuelle, Heinrich Benoit, Mery Stephane, Sleczkowski Piotr, Xiao Yiming, Lafolet Frederic, Hashizume Daisuke, Aoyama Tetsuya, Uchiyama Masanobu, Wu Jeong Weon, Zaborova Elena, Fages Frederic, D'Aleo Anthony, Mathevet Fabrice, Adachi Chihaya, A solvent-free and vacuum-free melt-processing method to fabricate organic semiconducting layers with large crystal size for organic electronic applications, JOURNAL OF MATERIALS CHEMISTRY C, 10.1039/c8tc04834g, 7, 11, 3190-3198, 2019.03. |
| 463. | Hiroki Noda ; Hajime Nakanotani; Chihaya Adachi, Highly Efficient Thermally Activated Delayed Fluorescence with Slow Reverse Intersystem Crossing, Chemistry Letters, 10.1246/cl.180813, 48, 2, 126-129, 2018.11, We report an efficient luminescent molecule exhibiting thermally activated delayed fluorescence with a long-delayed fluorescence lifetime of 0.8 ms. Although the reverse intersystem crossing rate constant is small at 2.1 x 10(3) s(-1), the molecule shows a high photoluminescence quantum yield of 89 +/- 2%, indicating the suppression of nonradiative decay from the triplet state.. |
| 464. | Hiroyuki Mieno; Ryota Kabe; Chihaya Adachi, Reversible control of triplet dynamics in metal-organic framework-entrapped organic emitters via external gases, Communications Chemistry, 10.1038/s42004-018-0027-x, 1, 27, 2018.01. |
| 465. | Naofumi Kobayashi, Hiroyuki Kuwae, Juro Oshima, Ryoichi Ishimatsu, Shuya Tashiro, Toshihiko Imato, Chihaya Adachi, Shuichi Shoji, Jun Mizuno, A wide-energy-gap naphthalene-based liquid organic semiconductor host for liquid deep-blue organic light-emitting diodes, Journal of Luminescence, 10.1016/j.jlumin.2018.03.072, 200, 19-23, 2018.08, We developed a novel naphthalene derivative to function as a wide-energy-gap liquid organic semiconductor (LOS) host material for the limited range of liquid deep-blue light-emitting materials that have been developed to date. The naphthalene derivative 1-naphthaleneacetic acid 2-ethylhexyl ester (NLQ), which shows a low viscosity of 20 mPa·s at 25 °C, was synthesized as a LOS by introducing an ethylhexyl group into naphthalene. We doped 9,10-diphenylanthracene (DPA) into NLQ as a guest deep-blue dye. The highest occupied molecular orbital (HOMO) energy level of NLQ was estimated to be − 6.40 eV from photoelectron spectroscopy measurements in air. The energy gap of NLQ was estimated to be 4.08 eV from its absorption spectrum, indicating that NLQ has the widest energy gap of any such host material to date. The lowest unoccupied molecular orbital energy level of NLQ was calculated to be − 2.31 eV. Deep-blue electroluminescence emission in a liquid state was obtained by doping DPA into NLQ. Light emission could be achieved by a combination of Förster resonance energy transfer and direct recombination of trapped holes and electrons because the energy gap of DPA is straddled by the wider energy gap of NLQ.. |
| 466. | Ribierre Jean-Charles, Tanaka Toshihiko, Zhao Li, Yokota Yuki, Matsumoto Shinya, Hashizume Daisuke, Takaishi Kazuto, Muto Tsuyoshi, Heinrich Benoit, Mery Stephane, Mathevet Fabrice, Matsushima Toshinori, Uchiyama Masanobu, Adachi Chihaya, Aoyama Tetsuya, Simultaneous Edge-on to Face-on Reorientation and 1D Alignment of Small pi-Conjugated Molecules Using Room-Temperature Mechanical Rubbing, Advanced Functional Materials, 10.1002/adfm.201707038, 28, 19, 2018.05. |
| 467. | Dae-Hyeon Kim, Anthony D'Aléo, Xian-Kai Chen, Atula D. S. Sandanayaka, Dandan Yao, Li Zhao, Takeshi Komino, Elena Zaborova, Gabriel Canard, Youichi Tsuchiya, Eunyoung Choi, Jeong Weon Wu, Frédéric Fages, Jean-Luc Brédas, Jean-Charles Ribierre, Chihaya Adachi, High-efficiency electroluminescence and amplified spontaneous emission from a thermally activated delayed fluorescent near-infrared emitter, Nature Photonics, 10.1038/s41566-017-0087-y, 12, 2, 98-104, 2018.02, Near-infrared organic light-emitting diodes and semiconductor lasers could benefit a variety of applications including night-vision displays, sensors and information-secured displays. Organic dyes can generate electroluminescence efficiently at visible wavelengths, but organic light-emitting diodes are still underperforming in the near-infrared region. Here, we report thermally activated delayed fluorescent organic light-emitting diodes that operate at near-infrared wavelengths with a maximum external quantum efficiency of nearly 10% using a boron difluoride curcuminoid derivative. As well as an effective upconversion from triplet to singlet excited states due to the non-adiabatic coupling effect, this donor-acceptor-donor compound also exhibits efficient amplified spontaneous emission. By controlling the polarity of the active medium, the maximum emission wavelength of the electroluminescence spectrum can be tuned from 700 to 780 nm. This study represents an important advance in near-infrared organic light-emitting diodes and the design of alternative molecular architectures for photonic applications based on thermally activated delayed fluorescence.. |
| 468. | Takashi Kobayashi, Akitsugu Niwa, Shota Haseyama, Kensho Takaki, Takashi Nagase, Kenichi Goushi, Chihaya Adachi, Hiroyoshi Naito, Emission properties of thermally activated delayed fluorescence emitters: Analysis based on a four-level model considering a higher triplet excited state, Journal of Photonics for Energy, 10.1117/1.JPE.8.032104, 8, 3, 2018.07, © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE). A four-level model consisting of a higher triplet excited state (T2), the lowest singlet and triplet excited states (S1 and T1), and the ground state was previously used to understand emission properties of a thermally activated delayed fluorescence (TADF) emitter, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN). In this report, we discuss the four-level model in more detail and apply to the other two TADF emitters, i.e., 1,2,4,5-tetrakis(carbazol-9-yl)-3,6-dicyanobenzene (4CzTPN) and 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN), in order to determine their excited-state structures. It is suggested that in all the emitters T2 lies between S1 and T1 and play an essential role in the emitting process. In 4CzTPN, phosphorescence from T2 is clearly observed around 100 K as in 4CzIPN. Compared to the other two emitters, 2CzPN has a wider energy gap between S1 and T1 so that delayed fluorescence at room temperature is thought to be mixed with phosphorescence. Because of this mixing, the spectrum characteristic of phosphorescence from T2 in 2CzPN cannot be identified.. |
| 469. | Nastaran Faraji, Chuanjiang Qin, Toshinori Matsushima, Chihaya Adachi, Jan Seidel, Grain Boundary Engineering of Halide Perovskite CH3NH3PbI3 Solar Cells with Photochemically Active Additives, Journal of Physical Chemistry C, 10.1021/acs.jpcc.8b00804, 122, 9, 4817-4821, 2018.03, In this study, we investigate the nanoscale effects of photochemically active additives of benzoquinone (BQ), hydroquinone (HQ), and tetracyanoquinodimethane (TCNQ) on grain boundaries in CH3NH3PbI3 solar cells. We employ scanning probe microscopy under light illumination, in particular Kelvin probe force microscopy, to study surface potential changes under laser light illumination. The recently found improvement in the efficiency of BQ added solar cells can be clearly seen in vanishing contact potential differences at grain boundaries under illumination, rendering the material more uniform under solar cell operating conditions. These effects are observed for BQ, but not for HQ and TCNQ. Our findings shed light onto halide perovskite materials and the functional additive design for improved solar cell performance.. |
| 470. | Y. Hasegawa, Y. Yamada, M. Sasaki, T. Hosokai, H. Nakanotani, C. Adachi, Well-Ordered 4CzIPN ((4s,6s)-2,4,5,6-Tetra(9-H-carbazol-9-yl)isophthalonitrile) Layers: Molecular Orientation, Electronic Structure, and Angular Distribution of Photoluminescence, Journal of Physical Chemistry Letters, 10.1021/acs.jpclett.7b03232, 9, 4, 863-867, 2018.02, We fabricated a well-ordered homogeneous monolayer of disk-shaped, carbazolyl dicyanobenzene (CDCB)-based thermally activated delayed fluorescence (TADF) molecule, i.e., 4CzIPN((4s,6s)-2,4,5,6-tetra(9Hcarbazol-9-yl)isophthalonitrile) at room temperature on flat Ag(111), Au(111), and Cu(111) surfaces. The second layer of the 4CzIPN was also found to be well ordered. The electronic states of the well-ordered monolayer and multilayer of 4CzIPN were found to be nearly unchanged from that of the isolated molecule calculated by the density functional theory (DFT), suggesting that the ordered layers retain the TADF properties. Indeed, we demonstrated the delayed fluorescence and the nearly perfect in-plane alignment of the transition dipole moment of a 4CzIPN thin film on glass substrate even in an ambient condition. These results indicate that the well-ordered films of the disc-shaped carbazole-based TADF molecules could potentially be utilized in organic light-emitting diode (OLED) devices with high light outcoupling efficiency.. |
| 471. | Paulius Baronas, Patrik Ščajev, Vladislavas Cerkasovas, Gediminas Kreiza, Povilas Adomenas, Ona Adomeniene, Karolis Kazlauskas, Chihaya Adachi, Saulius Juršenas, Exciton diffusion in bifluorene single crystals studied by light induced transient grating technique, Applied Physics Letters, 10.1063/1.5008376, 112, 3, 2018.01, Exciton diffusion is considered to be of prime importance for controlling the recombination zone in organic light emitting devices. This is particularly relevant for organic lasers based on single crystals, where undesirable exciton-exciton annihilation at high concentrations is inevitable. Here, exciton diffusion is studied in bifluorene single crystals specifically designed for organic laser applications, therefore featuring exceptionally low threshold of light amplification. The non-destructive light induced transient grating (LITG) technique capable of simultaneously evaluating the exciton lifetime and diffusion coefficient along different directions of the crystal was employed for this study. Highly anisotropic singlet exciton diffusion with the diffusion coefficient varying from < 0.05 up to 0.96 cm2/s (in a perpendicular direction) and the corresponding diffusion lengths changing from < 60 up to 300 nm, respectively, was revealed in ethylene-bridged bifluorene crystals. The LITG results on the directionality of exciton diffusion are anticipated to be essential for devising single crystal based organic lasers.. |
| 472. | Hao Ye, Linsong Cui, Toshinori Matsushima, Chuanjiang Qin, Chihaya Adachi, Deep-Red Amplified Spontaneous Emission from cis-Configured Squaraine, ACS Applied Materials and Interfaces, 10.1021/acsami.7b15562, 10, 1, 27-31, 2018.01, We report deep-red amplified spontaneous emission (ASE) from cis-configured squaraine (cis-DCSQ1) under optical pumping. Doping of cis-DCSQ1 into a 4,4′-bis(9-carbazolyl)-2,2′-biphenyl (CBP) host film at an appropriate concentration (0.5 wt % for this system) led to a marked increase of photoluminescence quantum yield because of efficient CBP-to-cis-DCSQ1 Förster resonance energy transfer and suppression of aggregation-caused quenching. Thus, this doped film showed clear ASE with a threshold of around 10 μJ cm-2 and peak wavelength of 687 nm. These results proved that cis-configured squaraine derivatives are promising as gain materials for future applications as deep-red organic lasers.. |
| 473. | Chin-Yiu Chan, Lin-Song Cui, Jong Uk Kim, Hajime Nakanotani, Chihaya Adachi, Rational Molecular Design for Deep-Blue Thermally Activated Delayed Fluorescence Emitters, Advanced Functional Materials, 10.1002/adfm.201706023, 28, 11, 2018.03, By simple modification of the functional groups on the donor unit, the thermally activated delayed fluorescence (TADF) properties of emitters can easily be manipulated. A series of deep blue to blue emissive TADF derivatives is developed, capable of deep-blue emissions from 403 to 460 nm in toluene. Deep-blue organic light-emitting diodes (OLEDs) based on this series of TADF emitters are fabricated, resulting in an electroluminescence peak at 428 nm and a high external quantum efficiency of up to 10.3%. One deep-blue OLED has achieved the commission internationale de l'eclairage (CIE) coordinates of (0.156, 0.063), which is among the best reported TADF performances for deep-blue OLEDs with CIEy < 0.07.. |
| 474. | Y. Olivier; B. Yurash; L. Muccioli; G. D’Avino; O. Mikhnenko; J. C. Sancho-García; C. Adachi; T.-Q. Nguyen; D. Beljonne, Nature of the singlet and triplet excitations mediating thermally activated delayed fluorescence, Physical Review Materials, 10.1103/PhysRevMaterials.1.075602, 1, 075602, 2017.05. |
| 475. | Paulius Baronas, Gediminas Kreiza, Povilas Adomenas, Ona Adomeniene, Karolis Kazlauskas, Jean-Charles Ribierre, Chihaya Adachi, Saulius Juršenas, Low-Threshold Light Amplification in Bifluorene Single Crystals: Role of the Trap States, ACS Applied Materials and Interfaces, 10.1021/acsami.7b14702, 10, 3, 2768-2775, 2018.01, Organic single crystals (SCs) expressing long-range periodicity and dense molecular packing are an attractive amplifying medium for the realization of electrically driven organic lasers. However, the amplified spontaneous emission (ASE) threshold (1-10 kW/cm2) of SCs is still significantly higher compared to those of amorphous neat or doped films. The current study addresses this issue by investigating ASE properties of rigid bridging group-containing bifluorene SCs. Introduction of the rigid bridges in bifluorenes enables considerable reduction of nonradiative decay, which, along with enhanced fluorescence quantum yield (72-82%) and short excited state lifetime (1.5-2.5 ns), results in high radiative decay rates (0.5 × 109 s-1) of the SCs, making them highly attractive for lasing applications. The revealed ASE threshold of 400 W/cm2 in acetylene-bridged bifluorene SCs is found to be among the lowest ever reported for organic crystals. Ultrafast transient absorption spectroscopy enabled one to disclose pronounced differences in the excited state dynamics of the studied SCs, pointing out the essential role of radiative traps in achieving a record low ASE threshold. Although the origin of the trap states was not completely unveiled, the obtained results clearly evidence that the crystal doping approach can be successful in achieving extremely low ASE thresholds required for electrically pumped organic laser.. |
| 476. | Lin-Song Cui, Shi-Bin Ruan, Fatima Bencheikh, Ryo Nagata, Lei Zhang, Ko Inada, Hajime Nakanotani, Liang-Sheng Liao, Chihaya Adachi, Long-lived efficient delayed fluorescence organic light-emitting diodes using n-type hosts, NATURE COMMUNICATIONS, 10.1038/s41467-017-02419-x, 8, 2017.12, Organic light-emitting diodes have become a mainstream display technology because of their desirable features. Third-generation electroluminescent devices that emit light through a mechanism called thermally activated delayed fluorescence are currently garnering much attention. However, unsatisfactory device stability is still an unresolved issue in this field. Here we demonstrate that electron-transporting n-type hosts, which typically include an acceptor moiety in their chemical structure, have the intrinsic ability to balance the charge fluxes and broaden the recombination zone in delayed fluorescence organic electroluminescent devices, while at the same time preventing the formation of high-energy excitons. The n-type hosts lengthen the lifetimes of green and blue delayed fluorescence devices by > 30 and 1000 times, respectively. Our results indicate that n-type hosts are suitable to realize stable delayed fluorescence organic electroluminescent devices.. |
| 477. | Yan Geng, Anthony D'Aleo, Ko Inada, Lin-Song Cui, Jong Uk Kim, Hajime Nakanotani, Chihaya Adachi, Donor-sigma-Acceptor Motifs: Thermally Activated Delayed Fluorescence Emitters with Dual Upconversion, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.201708876, 56, 52, 16536-16540, 2017.12, A family of organic emitters with a donor-sigma-acceptor (D-sigma-A) motif is presented. Owing to the weakly coupled D-sigma-A intramolecular charge-transfer state, a transition from the localized excited triplet state ((LE)-L-3) and charge-transfer triplet state ((CT)-C-3) to the charge-transfer singlet state ((CT)-C-1) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200-400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D-sigma-A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes.. |
| 478. | Yu Esaki, Takeshi Komino, Toshinori Matsushima, Chihaya Adachi, Enhanced Electrical Properties and Air Stability of Amorphous Organic Thin Films by Engineering Film Density, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 10.1021/acs.jpclett.7b02808, 8, 23, 5891-5897, 2017.12, The influences of film density and molecular orientation on the carrier conduction and air stability of vacuum-deposited amorphous organic films of N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (alpha-NPD) were investigated. The substrate temperature (T-sub) during vacuum deposition had different effects on the film density and molecular orientation of alpha-NPD. Film density was a concave function of T-sub; maximum density was attained at T-sub, = 270-300 K. alpha-NPD molecules were randomly oriented at T-sub, = 342 K, and their horizontal orientation on the substrate became dominant as T-sub:, decreased. Hole current and air stability were clearly raised by increasing the film density by 1 to 2%; these effects were, respectively, attributed to carrier hopping between neighboring alpha-NPD molecules and suppressed penetration of oxygen and water. These results imply that increasing film density is more effective to enhance the electrical performance of organic thin-film devices with alpha-NPD films than control of molecular orientation.. |
| 479. | Chuanjiang Qin, Toshinori Matsushima, Atula S. D. Sandanayaka, Youichi Tsuchiya, Chihaya Adachi, Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for Efficient and Stable Light-Emitting Diodes, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 10.1021/acs.jpclett.7b02371, 8, 21, 5415-5421, 2017.11, The optical, structural, and electroluminescent (EL) characteristics of pure quasi-2D CsPb2Br5 were reported. We fabricated continuous, compact, well-crystallized CsPb2Br5 films by centrifugal coating from a colloidal solution containing CsPb2Br5 nanoparticles. The centrifugal-coated CsPb2Br5 films have a photoluminescence quantum yield (PLQY) of similar to 35% because of its low-dimensional structure. Taking advantage of the high PLQY, we fabricated perovskite light-emitting diodes (PeLEDs) with a centrifugal coated CsPb2Br5 emitting layer exhibiting bright green EL, a maximum luminance of 7317 cd m(-2), an and external quantum efficiency of 1.1%. Additionally, the EL color could be changed easily from green to red using a halogen exchange method. The half lifetime of our CsPb2Br5 PeLEDs reached around 6 h under continuous operation at 10 mA cm(-2).. |
| 480. | Ryoichi Ishimatsu, Hirosato Shintaku, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Electrogenerated Chemiluminescence of a BODIPY Derivative with Extended Conjugation, CHEMISTRYSELECT, 10.1002/slct.201702449, 2, 32, 10531-10536, 2017.11, The electrochemical properties and electrogenerated chemiluminescence (ECL) of a borondipyrromethane (BODIPY) derivative, 2,8-bis(4-isopropylphenyl)-difuro[2,3-b][3,2-g]-5,5-difluoro-5-bora-3a,4a-diaza-s-indacene (Derivative 1, Figure) are described. Derivative 1 emitted ECL in the range of 650 similar to 800nm by using tripropylamine (TPA) as a coreactant. In the cyclic voltammogram, Derivative 1 showed a reversible oxidation wave, whereas the reduction wave was irreversible. Energetically, it is likely that triplet-triplet annihilation is the main pathway to emit ECL through the ion annihilation of the radical anions and cations of Derivative 1 whereas the lowest excited singlet state of Derivative 1 is directly produced with TPA. The maximum ECL wavelengths (670nm at 0.01mM) were red-shifted with increasing the concentration of Derivative 1 because of the self-absorption resulted from a small Stokes shift (similar to 10nm). Relative ECL efficiency of Derivative 1 was 0.13 compared to that of a Ru(bpy)(2+)/TPA system.. |
| 481. | Xian-Kai Chen, Youichi Tsuchiya, Yuma Ishikawa, Cheng Zhong, Chihaya Adachi, Jean-Luc Bredas, A New Design Strategy for Efficient Thermally Activated Delayed Fluorescence Organic Emitters: From Twisted to Planar Structures, ADVANCED MATERIALS, 10.1002/adma.201702767, 29, 46, 2017.12, In the traditional molecular design of thermally activated delayed fluorescence (TADF) emitters composed of electron-donor and electron-acceptor moieties, achieving a small singlet-triplet energy gap (Delta E-ST) in strongly twisted structures usually translates into a small fluorescence oscillator strength, which can significantly decrease the emission quantum yield and limit efficiency in organic light-emitting diode devices. Here, based on the results of quantum-chemical calculations on TADF emitters composed of carbazole donor and 2,4,6-triphenyl-1,3,5-triazine acceptor moieties, a new strategy is proposed for the molecular design of efficient TADF emitters that combine a small Delta E-ST with a large fluorescence oscillator strength. Since this strategy goes beyond the traditional framework of structurally twisted, charge-transfer type emitters, importantly, it opens the way for coplanar molecules to be efficient TADF emitters. Here, a new emitter, composed of azatriangulene and diphenyltriazine moieties, is theoretically designed, which is coplanar due to intramolecular H-bonding interactions. The synthesis of this hexamethylazatriangulene-triazine (HMAT-TRZ) emitter and its preliminary photophysical characterizations point to HMAT-TRZ as a potential efficient TADF emitter.. |
| 482. | Ryota Kabe, Chihaya Adachi, Organic long persistent luminescence, Nature, 10.1038/nature24010, 550, 7676, 384-387, 2017.10, Long persistent luminescence (LPL) materials - widely commercialized as 'glow-in-the-dark' paints - store excitation energy in excited states that slowly release this energy as light. At present, most LPL materials are based on an inorganic system of strontium aluminium oxide (SrAl 2 O 4) doped with europium and dysprosium, and exhibit emission for more than ten hours. However, this system requires rare elements and temperatures higher than 1,000 degrees Celsius during fabrication, and light scattering by SrAl 2 O 4 powders limits the transparency of LPL paints. Here we show that an organic LPL (OLPL) system of two simple organic molecules that is free from rare elements and easy to fabricate can generate emission that lasts for more than one hour at room temperature. Previous organic systems, which were based on two-photon ionization, required high excitation intensities and low temperatures. By contrast, our OLPL system - which is based on emission from excited complexes (exciplexes) upon the recombination of long-lived charge-separated states - can be excited by a standard white LED light source and generate long emission even at temperatures above 100 degrees Celsius. This OLPL system is transparent, soluble, and potentially flexible and colour-tunable, opening new applications for LPL in large-area and flexible paints, biomarkers, fabrics, and windows. Moreover, the study of long-lived charge separation in this system should advance understanding of a wide variety of organic semiconductor devices.. |
| 483. | Patrik Scajev, Ramunas Aleksiejunas, Saulius Miasojedovas, Saulius Nargelas, Munetomo Inoue, Chuanjiang Qin, Toshinori Matsushima, Chihaya Adachi, Saulius Jursenas, Two Regimes of Carrier Diffusion in Vapor-Deposited Lead-Halide Perovskites, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/acs.jpcc.7b04179, 121, 39, 21600-21609, 2017.10, Metal halide perovskites are attractive materials for the realization of cheap and effective solar cells, thin film transistors, and light emitters. Carrier diffusion at high excitations, however, is poorly addressed in perovskites, even though it governs the diffusion length and determines the efficiency of photonic devices. To fully understand the dependence of diffusion length on carrier density, we performed direct and independent measurements of the carrier diffusion coefficient and recombination rate in several methylammonium lead halide perovskite layers by applying the light-induced transient grating technique. We demonstrate the existence of two distinct carrier diffusion regimes within the density range of 10(18)-10(20) cm(-3). In the perovskite films of high compositional quality, diffusion is governed by a bandlike transport of free carriers. The diffusivity is high (0.28-0.7 cm(2)/s) in these samples, even at low carrier density, and further increases with excitation due to carrier degeneracy. The opposite scenario was observed in disordered perovskite layers, where diffusion is governed by hopping-like transport of localized carriers. The diffusion coefficient in latter layers is small (0.01-0.04 cm(2)/s at low densities) and increases with excitation due to local state filling and carrier delocalization. We show that carrier recombination can be well-described using the nonlinear radiative and nonradiative recombination coefficients that saturate with excitation due to phase space filling at high carrier densities. On the basis of these findings, we provide recommendations for the maximization of carrier diffusion length in different perovskites.. |
| 484. | Yan Geng, Lin-Song Cui, Jong Uk Kim, Hajime Nakanotani, Chihaya Adachi, Molecular Design for Blue Thermal Activated Delayed Fluorescence Materials: Substitution Position Effect, CHEMISTRY LETTERS, 10.1246/cl.170587, 46, 10, 1490-1492, 2017.10, Three emitters having a donor-phenyl-acceptor structure are considered as thermally activated delayed fluorescence (TADF) materials. They present different triplet excited-state energies depending on the substitution positions. Consequently, two materials exhibit blue emission with TADF properties. The OLEDs based on o-CzXTN provided a maximum EQE as high as 10.6%.. |
| 485. | Yan Qiong Zheng, Chao Wang, Jun Le Yu, Fang Yang, Bin Wei, Yang Lin, Xi Feng, Chihaya Adachi, Diindenoperylene (DIP) concentration dependent photovoltaic performance and dielectric properties for mixed heterojunctions, SYNTHETIC METALS, 10.1016/j.synthmet.2017.09.001, 233, 35-40, 2017.11, To find some intrinsic relevance between the photovoltaic performance and dielectric properties of diindenoperylene (DIP) mixed heterojunctions (MHJs), this work demonstrates both the photovoltaic performance and dielectric characteristic dependence on the DIP concentration. 5 wt%-DIP MHJ shows relatively higher performance compared to other MHJs with higher DIP ratio over the range of 5 wt%-90 wt%. The dielectric constant of blend layers decreases with the DIP ratio, thus results in larger Coulomb capture radius and exciton binding energy, which suppresses the exciton dissociation in MHJs with high DIP ratio. Then, the dielectric characteristic of capacitance-voltage (C-V) in dark and under illumination as well as of capacitance-frequency (C-f)at dc bias of 1.6 V for the DIP MHJs were measured. The geometric capacitance of the MHJs extracted from the C-V in dark indicates a positive dependence on the DIP concentration. C-V peak height decreases with the DIP concentration from 0 to 60 wt% implies that the hole drift becomes dominated at higher DIP content. The open circuit voltage (V-oc) of all the MHJs shows an identical trend with the normalized built-in potential. In dark condition, depletion width (W) gradually decreases with the DIP concentration from 5 wt% to 60 wt%. W becomes narrower under illumination, ascribed to the increased capacitance from photo-generated charge. The free carrier density (N-D) imposes a negative influence on fill factor of MHJs. The extracted electron mobility by C-f characteristic gradually decreases with the DIP ratio.. |
| 486. | Takeshi Komino, Yuji Oki, Chihaya Adachi, Dipole orientation analysis without optical simulation: application to thermally activated delayed fluorescence emitters doped in host matrix, SCIENTIFIC REPORTS, 10.1038/s41598-017-08708-1, 7, 2017.08, The dipole orientation of guest emitters doped into host matrices is usually investigated by angular dependent photoluminescence (PL) measurements, which acquire an out-of-plane PL radiation pattern of the guest-host thin films. The PL radiation patterns generated by these methods are typically analysed by optical simulations, which require expertise to perform and interpret in the simulation. In this paper, we developed a method to calculate an orientational order parameter S without the use of full optical simulations. The PL radiation pattern showed a peak intensity (I-sp) in the emission direction tilted by 40 degrees-60 degrees from the normal of the thin film surface plane, indicating an inherent dipole orientation of the emitter. Thus, we directly correlated I-sp with S. The S - I-sp relation was found to depend on the film thickness (d) and refractive indices of the substrate (n(sub)) and the organic thin film (n(org)). Hence, S can be simply calculated with information of I-sp, d, n(sub), and n(org). We applied our method to thermally activated delayed fluorescence materials, which are known to be highly efficient electroluminescence emitters. We evaluated S and found that the error of this method, compared with an optical simulation, was less than 0.05.. |
| 487. | Naoto Notsuka, Ryota Kabe, Kenichi Goushi, Chihaya Adachi, Confinement of Long-Lived Triplet Excitons in Organic Semiconducting Host-Guest Systems, Advanced Functional Materials, 10.1002/adfm.201703902, 27, 40, 1703902, 2017.10. |
| 488. | Masashi Mamada, Ko Inada, Takeshi Komino, William J. Potscavage, Hajime Nakanotani, Chihaya Adachi, Highly Efficient Thermally Activated Delayed Fluorescence from an Excited-State Intramolecular Proton Transfer System, ACS CENTRAL SCIENCE, 10.1021/acscentsci.7b00183, 3, 7, 769-777, 2017.07, Thermally activated delayed fluorescence (TADF) [GRAPHIC] materials have shown great potential for highly efficient organic light-emitting diodes (OLEDs). While the current molecular design of TADF materials primarily focuses on combining donor and acceptor units, we present a novel system based on the use of excited-state intramolecular proton transfer (ESIPT) to achieve efficient TADF without relying on the well-established donor-acceptor scheme. In an appropriately designed acridone-based compound with intramolecular hydrogen bonding, ESIPT leads to separation of the highest occupied and lowest unoccupied molecular orbitals, resulting in TADF emission with a photoluminescence quantum yield of nearly 60%. High external electroluminescence quantum efficiencies of up to 14% in OLEDs using this emitter prove that efficient triplet harvesting is possible with ESIPT-based TADF materials. This work will expand and accelerate the development of a wide variety of TADF materials for high performance OLEDs.. |
| 489. | Alessia Senes, Stefan C. J. Meskers, Horst Greiner, Katsuaki Suzuki, Hironori Kaji, Chihaya Adachi, Joanne S. Wilson, Rene A. J. Janssen, Increasing the horizontal orientation of transition dipole moments in solution processed small molecular emitters, JOURNAL OF MATERIALS CHEMISTRY C, 10.1039/c7tc01568b, 5, 26, 6555-6562, 2017.07, The efficiency of organic light emitting diodes (OLEDs) can be improved by controlling the orientation of the transition dipole moment of the emitters. Currently, no effective methods exist for orienting the transition dipole moments in solution processed active layers for OLEDs. We investigate the orientation of the transition dipole moment of small molecular emitters in a host matrix of poly(9,9-dioctylfluorene) (PFO) by means of angle dependent luminescence intensity measurements. The polymer chains of the host orient predominantly in the plane of the film. Fluorescent p-phenylenevinylene oligomers with 6 and 7 repeat units (OPV6, OPV7) are found to also orient preferentially horizontally. The orientation of the emitters can be improved by thermal annealing with up to 90% of transition dipole moments oriented in the plane of the film. The phosphorescent emitter Ir(MDQ)(2)(acac) shows a degree of horizontal orientation in the polymeric host matrix lower than that which is observed for oligomers, but as high as is observed for the same emitter in evaporated layers. A carbazole derivative capable of thermally activated delayed fluorescence shows a small preference for vertical orientation within the polymer host. The strong orientation of OPV6 and OPV7 in the oriented polymer host is rationalized in terms of their high aspect ratios. The use of PFO as host material in host/guest systems allows achieving horizontal orientation of transition dipole moments in solution processed oligomers and small molecular emitters.. |
| 490. | F. Bencheikh, A. S. D. Sandanayaka, T. Matsushima, J. C. Ribierre, C. Adachi, Influence of the organic film thickness on the second order distributed feedback resonator properties of an organic semiconductor laser, JOURNAL OF APPLIED PHYSICS, 10.1063/1.4986504, 121, 23, 2017.06, We report on the cavity numerical characterization of a second order one-dimensional distributed feedback organic laser. The gain medium containing 6wt. % of 4,4'bis[(N-carbazole) styryl] biphenyl) in a 4,4;-bis[9-dicarbazolyl]-2,2'-biphenyl) host is vacuum deposited to form an organic thin film on a SiO2 grating. The influence of the organic film thickness on the properties of the resonant cavity is investigated through numerical calculations of both the confinement factor Gamma and the Q-factor. The Q-factor is obtained using two methods, one by calculating the eigenmodes of the resonant cavity and the other by calculating the reflection spectrum. It was found that while the Gamma increases with the organic film thickness, the Q-factor shows a non-monotonic function with a maximum value for a thickness of 200 nm. Published by AIP Publishing.. |
| 491. | Jong Uk Kim, Saripally Sudhaker Reddy, Lin-Song Cui, Hiroko Nomura, Sunbin Hwang, Dae Hyeon Kim, Hajime Nakanotani, Sung-Ho Jin, Chihaya Adachi, Thermally activated delayed fluorescence of Bis(9,9-dimethy1-9,10-dihydroacridine) dibenzo [b,d]thiophene 5,5-dioxide derivatives for organic light-emitting diodes, JOURNAL OF LUMINESCENCE, 10.1016/j.jlumin.2017.06.006, 190, 485-491, 2017.10, Two luminescent dibenzo [b,d] thiophene 5,5-dioxide derivatives combined with 9,9-dimethyl-9,10-dihydroacridine were synthesized and the appearance of thermally activated delayed fluorescence was confirmed. Both 3,7- and 2,8-bis(9,9-dimethy1-9,10-dihydroacridine)dibenzo [b,d]thiophene 5,5-dioxide (3ASOA) and (4ASOA) showed prompt and delayed fluorescence with high total photoluminescence (PL) quantum efficiencies of 72% and 88% in their doped films, respectively. The maximum external electroluminescence (EL) efficiencies of 13.8% in 4ASOA and 10.4% in 3ASOA were obtained. Further, 4ASOA showed slightly relaxed rolloff behavior, indicating that 2,8-substitution of the donors appreciably improved both PL and EL characteristics.. |
| 492. | Kou Yoshida; Toshinori Matsushima; Yu Shiihara; Hiroyuki Kuwae; Jun Mizuno; Chihaya Adachi, Joule heat-induced breakdown of organic thin-film devices under pulse operation, J. Appl. Phys., 10.1063/1.4983456, 121, 195503, 2017.05. |
| 493. | Toshinori Matsushima, Sunbin Hwang, Shinobu Terakawa, Takashi Fujihara, Atula S. D. Sandanayaka, Chuanjiang Qin, Chihaya Adachi, Intrinsic carrier transport properties of solution-processed organic-inorganic perovskite films, APPLIED PHYSICS EXPRESS, 10.7567/APEX.10.024103, 10, 2, 2017.02, The true performance of field-effect transistors with spin-coated organic-inorganic perovskite (C6H5C2H4NH3)(2)Snl(4) semiconductor layers remains unknown because of the presence of contact resistance ( RC). To evaluate the intrinsic carrier mobility (mu), we fabricated perovskite transistors with large channel lengths (L). The field-effect mu gradually increased with increasing L and then became constant in the large-L region, because of the reduced contribution of RC relative to the total resistance. The intrinsic mu values estimated from this region reached 26 and 4.8 cm(2)V(-1) s(-1) for holes and electrons, respectively, which are the highest ever reported in any perovskite transistor. (C) 2017 The Japan Society of Applied Physics. |
| 494. | T. Fujihara, S. Terakawa, T. Matsushima, C. Qin, M. Yahiro, C. Adachi, Fabrication of high coverage MASnI(3) perovskite films for stable, planar heterojunction solar cells, JOURNAL OF MATERIALS CHEMISTRY C, 10.1039/c6tc05069g, 5, 5, 1121-1127, 2017.02, The development of lead-free organic-inorganic perovskite absorbers for solar cells is an important step toward commercializing this technology. Tin halide perovskites are a proposed alternative to lead perovskites; however, their performances show high levels of instability owing to the low quality of these perovskite films. In this work, we used a modified solvent bathing method to fabricate tin halide perovskite films. To control the formation speed of the perovskite films, we combined anti-solvents with miscibilities different to those of the precursor solvent in an appropriate ratio and at an appropriate temperature. Thus, we were able to significantly improve the coverage of the perovskite films. A planar perovskite solar cell with a film prepared using this method showed an efficiency of 2.14 +/- 0.35% with an open circuit voltage of 0.45 +/- 0.01 V, which is higher than that of solar cells with a conventionally prepared active layer. Additionally, we achieved a significant reproducibility in performance in comparison with previously reported devices. Further, the solar cells had unexpectedly long lifetimes of over 200 h under 1 Sun degradation conditions (AM1.5, 100 mW cm(-2)); generally, tin perovskites degrade quickly. We propose that the comparably high open circuit voltage and stable photovoltaic properties of our tin halide perovskite solar cells is the result of the high surface coverage of the perovskite film, which was achieved using the modified solvent bathing method.. |
| 495. | D. -H. Kim, A. S. D. Sandanayaka, L. Zhao, D. Pitrat, J. C. Mulatier, T. Matsushima, C. Andraud, J. C. Ribierre, C. Adachi, Extremely low amplified spontaneous emission threshold and blue electroluminescence from a spin-coated octafluorene neat film, APPLIED PHYSICS LETTERS, 10.1063/1.4974045, 110, 2, 2017.01, We report on the photophysical, amplified spontaneous emission (ASE), and electroluminescence properties of a blue-emitting octafluorene derivative in spin-coated films. The neat film shows an extremely low ASE threshold of 90 nJ/cm(2), which is related to its high photoluminescence quantum yield of 87% and its large radiative decay rate of 1.7 x 10(9) s(-1). Low-threshold organic distributed feedback semiconductor lasers and fluorescent organic light-emitting diodes with a maximum external quantum efficiency as high as 4.4% are then demonstrated, providing evidence that this octafluorene derivative is a promising candidate for organic laser applications. Published by AIP Publishing.. |
| 496. | D. H. Kim, K. Inada, L. Zhao, T. Komino, N. Matsumoto, J. C. Ribierre, C. Adachi, Organic light emitting diodes with horizontally oriented thermally activated delayed fluorescence emitters, JOURNAL OF MATERIALS CHEMISTRY C, 10.1039/c6tc04786f, 5, 5, 1216-1223, 2017.02, Horizontal orientation of the emission transition dipole of light-emitting molecules plays a critical role in the light outcoupling efficiency and the performance of organic light-emitting diodes. It is well established that linear and planar small molecules are generally preferred to achieve such a horizontal molecular orientation in vapor-deposited organic thin films. Here, we designed and synthesized four novel carbazole-based thermally-activated delayed fluorescence (TADF) molecules with different shapes and degrees of planarity in order to examine the influence of the emitter structure on the molecular orientation and the electroluminescence properties in TADF OLEDs. Molecular orientation of the TADF molecules in neat films and in blends was investigated using variable angle spectroscopic ellipsometry and angle dependent photoluminescence measurements, respectively. The results provide new important insights into the influence of the planarity of TADF molecules on their molecular orientation in vapor-deposited organic thin films. The photophysical and electroluminescence properties of these TADF molecules were then investigated to examine the influence of the molecular orientation on the performance of TADF OLEDs. The most efficient device was obtained using the TADF emitter showing a nearly perfect horizontal orientation of the emitting dipoles in the blend films. The maximum electroluminescence external quantum efficiency measured in this device was found to be 15.4%, which is about 1.75 times higher than the theoretical value calculated using an isotropic distribution of transition dipoles.. |
| 497. | Gediminas Kreiza, Paulius Baronas, Edvinas Radiunas, Povilas Adomenas, Ona Adomeniene, Karolis Kazlauskas, Jean-Charles Ribierre, Chihaya Adachi, Saulius Jursenas, Bifluorene Single Crystals with Extremely Low-Threshold Amplified Spontaneous Emission, ADVANCED OPTICAL MATERIALS, 10.1002/adom.201600823, 5, 5, 2017.03, Organic single crystals offering numerous advantages due to their long-range molecular order are considered a promising gain medium for realization of electrically-pumped organic lasers provided their amplified spontaneous emission (ASE) threshold is sufficiently low. Unfortunately, ASE thresholds of such crystals are typically more than one order of magnitude higher (in the range of tens of kW cm(-2)) as compared to those of amorphous neat/doped films. Here, this issue is addressed by rationally designing bifluorene-based compounds to express weak intermolecular coupling in the crystalline phase. The twisted molecular backbone as well as out-of-plane twisted dimethyl moieties attached at the fluorene end-groups additionally benefit with enhanced electron-vibronic coupling resulting in a large Stokes shift (0.5 eV) and reduced reabsorption of emission. Endowed with such features the bifluorenes exhibit similarly high radiative decay rates (approximate to 1.5 x 10(9) s(-1)) when doped in polystyrene matrix at low concentrations and in sublimation-grown single crystals. The high radiative rates accompanied by excellent waveguiding properties, favorable orientation of transition dipole moments as well as non-overlapping excited-state absorption and gain regions enable achieving extremely low ASE thresholds (approximate to 700 W cm(-2)) in the bifluorene single crystals. The achieved low threshold encourages employment of rationally designed molecules in organic crystals for lasing applications.. |
| 498. | Hideaki Komiyama, Chihaya Adachi, Takuma Yasuda, Tetrathienoanthracene-based pi-Extended Narrow-band-gap Molecules: Synthesis, Physicochemical, and Photovoltaic Properties, CHEMISTRY LETTERS, 10.1246/cl.160858, 46, 1, 29-31, 2017.01, New acceptor-donor-acceptor-structured pi-extended narrow-band-gap molecules based on tetrathienoanthracene were designed and synthesized. Organic solar cells based on bulk-heterojunction blends of these molecules with PC61BM showed high open-circuit voltages of up to 0.97V.. |
| 499. | Lin-Song Cui, Hiroko Nomura, Yan Geng, Jong Uk Kim, Hajime Nakanotani, Chihaya Adachi, Controlling Singlet-Triplet Energy Splitting for Deep-Blue Thermally Activated Delayed Fluorescence Emitters, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.201609459, 56, 6, 1571-1575, 2017.02, The development of efficient metal-free organic emitters with thermally activated delayed fluorescence (TADF) properties for deep-blue emission is still challenging. A new family of deep-blue TADF emitters based on a donor-acceptor architecture has been developed. The electronic interaction between donor and acceptor plays a key role in the TADF mechanism. Deep-blue OLEDs fabricated with these TADF emitters achieved high external quantum efficiencies over 19.2% with CIE coordinates of (0.148, 0.098).. |
| 500. | Jiyoung Lee, Naoya Aizawa, Masaki Numata, Chihaya Adachi, Takuma Yasuda, Versatile Molecular Functionalization for Inhibiting Concentration Quenching of Thermally Activated Delayed Fluorescence, ADVANCED MATERIALS, 10.1002/adma.201604856, 29, 4, 2017.01, Concentration quenching of thermally activated delayed fluorescence is found to be dominated by electron-exchange interactions, as described by the Dexter energy-transfer model. Owing to the short-range nature of the electronexchange interactions, even a small modulation in the molecular geometric structure drastically affects the concentration- quenching, leading to enhanced solid-state photoluminescence and electroluminescence quantum efficiencies.. |
| 501. | Nagata R, Nakanotani H, Adachi C, Near-Infrared Electrophosphorescence up to 1.1 µm using a Thermally Activated Delayed Fluorescence Molecule as Triplet Sensitizer., Advanced materials (Deerfield Beach, Fla.), 10.1002/adma.201604265, 29, 5, 2017.02. |
| 502. | Chuanjiang Qin, Toshinori Matsushima, Takashi Fujihara, Chihaya Adachi, Multifunctional Benzoquinone Additive for Efficient and Stable Planar Perovskite Solar Cells, ADVANCED MATERIALS, 10.1002/adma.201603808, 29, 4, 2017.01, Device stability of planar perovskite solar cells is improved by virtue of multifunctional BQ additive. The morphology and crystal quality of the perovskite films are improved because BQ slows the rate of perovskite crystal formation. Electron transfer from perovskite to BQ reduces charge-recombination losses, and the oxidizing ability of BQ effectively suppresses the formation of metallic lead and improves device lifetime.. |
| 503. | Rampal Pandey, Gabor Mehes, Ashish Kumar, Roop Shikha Singh, Amit Kumar, Chihaya Adachi, Daya Shankar Pandey, Strong luminescence behavior of mono- and dimeric imidazoquinazolines: Swift OLED degradation under electrical current, JOURNAL OF LUMINESCENCE, 10.1016/j.jlumin.2016.09.026, 181, 252-260, 2017.01, Design and synthesis of novel mono-and dimeric quinazoline derivatives (+)-6-methyl-6-pyridin-2-yl-5,6-dihydrobenzo[4,5]imidazo[1,2-c]quinazoline (1) and (+)-6-[(6-methyl-5,6-dihydrobenzo-[4,5]imidazo [1,2-c] quinazolin-6-yl)-pyridin-2-yl]-6-methyl-5,6-dihydro-benzo-[4,5]imidazo-[1,2-c] quinazoline (2) have been described. Both 1 and 2 have been characterized by elemental analyses, FT-IR, H-1 and C-13 NMR, HRMS spectroscopic studies and their structures authenticated by X-ray single crystal analyses. Photophysical properties of these compounds have been studied by UV/VIS absorption and fluorescence spectroscopy and transient photoluminescence analysis in solution, powder, and non-doped (neat) and doped vacuum-deposited films. A broad emission spectrum spanning most of the visible range and good thermal stability indicated promising application of 1 and 2 as OLED emitters. Unfortunately, under current flow we observed rapid device degradation, presumably to be related to free -NH moiety in these compounds. (C) 2016 Elsevier B.V. All rights reserved.. |
| 504. | Yanqiong Zheng, Fang Yang, Chao Wang, Jing Zhang, William J. Potscavage, Bin Wei, Chihaya Adachi, Wenhong Pu, Changzhu Yang, Jianhua Zhang, Effect of 3,4,9,10-perylenetetracarboxylic bisbenzimidazole (PTCBI) as well as bathocuproine (BCP) and Ag interlayer thickness on the performance of organic tandem solar cells, SYNTHETIC METALS, 10.1016/j.synthmet.2016.09.001, 221, 179-185, 2016.11, Firstly, multi-fold subphthalocyanine (SubPc) homo-tandem cells were fabricated. When complementary absorbing SubPc and chloroaluminum phthalocyanine (ClAlPc) were used to prepare tandem cells, both short circuit current (J(sc)) and fill factor (FF) are significantly improved relative to the SubPc double tandem cell. 3,4,9,10-perylenetetracarboxylic bisbenzimidazole (PTCBI) as electron transporting layer (ETL) in the charge recombination zone (CRZ) achieves a much higher FF than bathocuproine (BCP) thus higher power conversion efficiency (eta(PCE)) in both the normal and reverse tandem cells, ascribed to the matched energy levels, very smooth film surface, and ohmic contact with Ag interlayer. The effect of Ag interlayer thickness was also investigated. Ultrathin Ag layer with isolated clusters is helpful for obtaining higher photocurrent in both PTCBI and BCP based CRZs, originating from a flatter interface, less optical loss, and a plasmonic effect induced absorption enhancement of C-60 in bottom subcell. By optical modeling for current matching, the performance of normal tandem cell is improved, exhibiting a high open circuit voltage of 1.80 V and an overall eta(PCE) of 3.49%. (C) 2016 Elsevier B.V. All rights reserved.. |
| 505. | Harunobu Takeda, Cong Chen, Takeshi Komino, Hiroaki Yoshioka, Yuji Oki, Chihaya Adachi, 0.6-1.6 THz band spectroscopy of organic thermally activated delayed fluorescence materials, OPTICAL MATERIALS EXPRESS, 10.1364/OME.6.003045, 6, 10, 3045-3052, 2016.10, Newly developed thermally activated delayed fluorescence (TADF) materials are attractive for application in efficient displays. Five TADF materials, including PXZ-TRZ and four carbazolyl dicyanobenzene (CDCB) derivatives of 4CzTPN, 4CzTPN - Ph, 2CzPN, and 4CzIPN, were investigated using terahertz spectroscopy in the 0.60-1.60 THz range. While PXZ-TRZ was almost transparent, the carbazolyl dicyanobenzene (CDCB) derivatives, especially 4CzIPN, exhibited intrinsic absorption features. Comparing these results with density functional theorem calculations, each absorption feature was clarified to originate from the intramolecular motions of the carbazole units. (C) 2016 Optical Society of America. |
| 506. | Toshinori Matsushima, Munetomo Inoue, Takashi Fujihara, Shinobu Terakawa, Chuanjiang Qin, Atula S. D. Sandanayaka, Chihaya Adachi, High-coverage organic-inorganic perovskite film fabricated by double spin coating for improved solar power conversion and amplified spontaneous emission, CHEMICAL PHYSICS LETTERS, 10.1016/j.cplett.2016.08.067, 661, 131-135, 2016.09, We demonstrate that double spin coating, where a perovskite film is covered with another perovskite film, can increase substrate coverage from 81% to 97% along with an increase of film thickness from 151 +/- 17 to 246 +/- 18 nm. The increased substrate coverage by double coating improves the solar power conversion efficiency from 7.1 +/- 0.6 to 10.3 +/- 1.0%, an approximate 1.5-fold increase. Additionally, a double-coated film of higher substrate coverage exhibits amplified spontaneous emission (ASE) while a single-coated film of lower substrate coverage does not exhibit ASE. Double coating is an attractive method for increasing substrate coverage and improving solar power conversion and ASE. (C) 2016 Elsevier B.V. All rights reserved.. |
| 507. | Toshinori Matsushima, Sunbin Hwang, Atula S. D. Sandanayaka, Chuanjiang Qin, Shinobu Terakawa, Takashi Fujihara, Masayuki Yahiro, Chihaya Adachi, Solution-Processed Organic-Inorganic Perovskite Field-Effect Transistors with High Hole Mobilities, ADVANCED MATERIALS, 10.1002/adma.201603126, 28, 46, 10275-10281, 2016.12, A very high hole mobility of 15 cm(2) V-1 s(-1) along with negligible hysteresis are demonstrated in transistors with an organic-inorganic perovskite semiconductor. This high mobility results from the well-developed perovskite crystallites, improved conversion to perovskite, reduced hole trap density, and improved hole injection by employing a top-contact/top-gate structure with surface treatment and MoOx hole-injection layers.. |
| 508. | Nobuhiro Yanai; Mariko Kozue; Shogo Amemori; Ryota Kabe; Chihaya Adachi; Nobuo Kimizuka, Increased Vis-to-UV upconversion performance by energy level matching between a TADF donor and high triplet energy acceptors, J. Mater. Chem. C, 10.1039/C6TC01816E, 4, 27, 6447-6451, 2016.05. |
| 509. | Takuya Hosokai, Hiroyuki Matsuzaki, Hajime Nakanotani, Katsumi Tokumaru, Tetsuo Tsutsui, Akihiro Furube, Keirou Nasu, Hiroko Nomura, Masayuki Yahiro, Chihaya Adachi, Evidence and mechanism of efficient thermally activated delayed fluorescence promoted by delocalized excited states, SCIENCE ADVANCES, 10.1126/sciadv.1603282, 3, 5, 2017.05, The design of organic compounds with nearly no gap between the first excited singlet (S-1) and triplet (T-1) states has been demonstrated to result in an efficient spin-flip transition from the T-1 to S-1 state, that is, reverse intersystem crossing (RISC), and facilitate light emission as thermally activated delayed fluorescence (TADF). However, many TADF molecules have shown that a relatively appreciable energy difference between the S-1 and T-1 states (similar to 0.2 eV) could also result in a high RISC rate. We revealed from a comprehensive study of optical properties of TADF molecules that the formation of delocalized states is the key to efficient RISC and identified a chemical template for these materials. In addition, simple structural confinement further enhances RISC by suppressing structural relaxation in the triplet states. Our findings aid in designing advanced organic molecules with a high rate of RISC and, thus, achieving the maximum theoretical electroluminescence efficiency in organic light-emitting diodes.. |
| 510. | A. D'Aleo, M. H. Sazzad, D. H. Kim, E. Y. Choi, J. W. Wu, G. Canard, F. Fages, J. -C. Ribierre, C. Adachi, Boron difluoride hemicurcuminoid as an efficient far red to near-infrared emitter: toward OLEDs and laser dyes, CHEMICAL COMMUNICATIONS, 10.1039/c7cc01786c, 53, 52, 7003-7006, 2017.07, A hemicurcuminoid boron difluoride complex is used as an emitter in organic light-emitting diodes, showing far red/near-infrared electroluminescence with an external quantum efficiency as high as 2.1%. This dye blended in CBP thin films shows amplified spontaneous emission with a threshold of 22 mu J cm(-2) at 750 nm, making this compound attractive for organic semiconductor lasers operating in the near-infrared region.. |
| 511. | Atula S. D. Sandanayaka, Toshinori Matsushima, Fatima Bencheikh, Kou Yoshida, Munetomo Inoue, Takashi Fujihara, Kenichi Goushi, Jean-Charles Ribierre, Chihaya Adachi, Toward continuous-wave operation of organic semiconductor lasers, SCIENCE ADVANCES, 10.1126/sciadv.1602570, 3, 4, 2017.04, The demonstration of continuous-wave lasing from organic semiconductor films is highly desirable for practical applications in the areas of spectroscopy, data communication, and sensing, but it still remains a challenging objective. We report low-threshold surface-emitting organic distributed feedback lasers operating in the quasicontinuous-wave regime at 80 MHz as well as under long-pulse photoexcitation of 30 ms. This outstanding performance was achieved using an organic semiconductor thin film with high optical gain, high photoluminescence quantum yield, and no triplet absorption losses at the lasing wavelength combined with a mixed-order distributed feedback grating to achieve a low lasing threshold. A simple encapsulation technique greatly reduced the laser-induced thermal degradation and suppressed the ablation of the gain medium otherwise taking place under intense continuous-wave photoexcitation. Overall, this study provides evidence that the development of a continuous-wave organic semiconductor laser technology is possible via the engineering of the gain medium and the device architecture.. |
| 512. | Kou Yoshida; Toshinori Matsushima; Yu Shiihara; Hiroyuki Kuwae; Jun Mizuno; Chihaya Adachi, Joule heat-induced breakdown of organic thin-film devices under pulse operation, J. Appl. Phys., 10.1063/1.4983456, 121, 195503, 2017.05. |
| 513. | Kazuya Jinnai, Ryota Kabe, Chihaya Adachi, A near-infrared organic light-emitting diode based on an Yb(III) complex synthesized by vacuum co-deposition, CHEMICAL COMMUNICATIONS, 10.1039/c7cc01580a, 53, 39, 5457-5460, 2017.05, Yb(DBM)(3)(DPEPO), an emitter, was directly synthesized on a substrate by the vacuum co-deposition of the precursor Yb(DBM)(3)(H2O)(2) and the ligand DPEPO. OLEDs incorporating the co-deposited emitting layer (Yb(DBM)(3)(H2O)(2) : DPEPO molar ratio = 1 : 1) achieved an eta(EQE) value of 0.15% at 1.0 mA cm(-2).. |
| 514. | Shota Haseyama, Akitsugu Niwa, Takashi Kobayashi, Takashi Nagase, Kenichi Goushi, Chihaya Adachi, Hiroyoshi Naito, Control of the Singlet–Triplet Energy Gap in a Thermally Activated Delayed Fluorescence Emitter by Using a Polar Host Matrix, Nanoscale Research Letters, 10.1186/s11671-017-2012-1, 12, 1, 268, 2017.12, © 2017, The Author(s). The photoluminescence properties of a thermally activated delayed fluorescence emitter, 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN), doped in a host matrix consisting of 1,3-bis(9-carbazolyl)benzene and a polar inert molecule, camphoric anhydride (CA), in various concentrations have been investigated. It is found that the addition of CA stabilizes only the lowest singlet excited state (S1) of 2CzPN without changing the energy level of the lowest triplet excited state (T1), leading to a reduction in the energy gap between S1and T1. The maximum reduction of energy gap achieved in this work has been determined to be around 65 meV from the shift of the fluorescence spectrum and the temperature dependence of the photoluminescence decay rate.. |
| 515. | Hajime Nakanotani, Taro Furukawa, Takuya Hosokai, Takuji Hatakeyama, Chihaya Adachi, Light Amplification in Molecules Exhibiting Thermally Activated Delayed Fluorescence, Advanced Optical Materials, 10.1002/adom.201700051, 5, 12, 1700051-1700051, 2017.05. |
| 516. | Takashi Kobayashi, Akitsugu Niwa, Kensho Takaki, Shota Haseyama, Takashi Nagase, Kenichi Goushi, Chihaya Adachi, Hiroyoshi Naito, Contributions of a Higher Triplet Excited State to the Emission Properties of a Thermally Activated Delayed-Fluorescence Emitter, PHYSICAL REVIEW APPLIED, 10.1103/PhysRevApplied.7.034002, 7, 3, 2017.03, The temperature dependences of photoluminescence (PL) decay rates and the PL spectrum of a thermally activated delayed-fluorescence emitter, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), are investigated. It is found that not only the lowest singlet (S-1) and triplet ( T-1) excited states but also an additional triplet excited state ( T-n) lying between S-1 and T-1 play an important role in the exciton decay process, particularly around 100 K. At around this temperature, some of the triplet excitons are thermally activated into Tn but not up to S-1, and they then decay into the ground state (S-0) with phosphorescence emission. Therefore, two kinds of phosphorescence, originating from T-n and T-1, are observed. The temperature dependence of the PL decay rates of 4CzIPN can be explained by a four-level model consisting of S-1, T-1, T-n, and S-0, and its energy gaps between T-n and T-1 and between S-1 and T-1 are determined to be 45 +/- 5 meV and 135 +/- 10 meV, respectively.. |
| 517. | Moon, C, Suzuki, K, Shizu, K, Adachi, C, Kaji, H, Kim, J, 【2017-3】Combined Inter- and Intramolecular Charge-Transfer Processes for Highly Efficient Fluorescent Organic Light-Emitting Diodes with Reduced Triplet Exciton Quenching, Adv. Mater., 10.1002/adma.201606448, 29, 17, [1606448-1]-[1606448-5], 2017.03. |
| 518. | Afshin Shahalizad, Anthony D'Aleo, Chantal Andraud, Muhammad Hasnan Sazzad, Dae-Hyeon Kim, Youichi Tsuchiya, Jean-Charles Ribierre, Jean-Michel Nunzi, Chihaya Adachi, Near infrared electroluminescence from Nd(TTA)(3) phen in solution-processed small molecule organic light-emitting diodes, ORGANIC ELECTRONICS, 10.1016/j.orgel.2017.01.044, 44, 50-58, 2017.05, We report on the near infrared electroluminescence properties of a Nd3+ complex with thenoyltri-fluoroacetone and 1,10-phenantroline ligands in solution-processed organic light-emitting diodes. Spincoated blends containing a 1,3-bis(9-carbazolyl) benzene host doped with the Nd3+ complex were found to exhibit a photoluminescence quantum yield of about 0.5%, regardless of the doping concentration level. Electroluminescent devices based on these small molecule blends showed the characteristic emission of Nd3+ at 890, 1060 and 1330 nm with an external quantum efficiency as high as 0.022%. These improved performances were mainly attributed to direct charge trapping and exciton formation on the near infrared emitter. Importantly, the efficiency roll-off at high current densities due to triplet-triplet exciton annihilation in the device containing 20 wt% of the complex was lower than what is typically observed in lanthanide complex-based electroluminescent devices. This is presumably due to the high triplet energy of the host material, which prevents guest-to-host energy-back transfer and thus host-guest triplet-triplet exciton annihilation. (C) 2017 Elsevier B. V.. |
| 519. | T. Fujihara; S. Terakawa; T. Matsushima; C. Qin; M. Yahiro; C. Adachi, Fabrication of high coverage MASnI3 perovskite films for stable, planar heterojunction solar cells, J. Mater. Chem. C, 10.1039/C6TC05069G, 5, 1121-1127, 2017.01. |
| 520. | Hiroshi Fujimoto, Takashi Suekane, Katsuya Imanishi, Satoshi Yukiwaki, Hong Wei, Kaori Nagayoshi, Masayuki Yahiro, Chihaya Adachi, Influence of vacuum chamber impurities on the lifetime of organic light-emitting diodes, SCIENTIFIC REPORTS, 10.1038/srep38482, 6, 38482, 2016.12, We evaluated the influence of impurities in the vacuum chamber used for the fabrication of organic light-emitting diodes on the lifetime of the fabricated devices and found a correlation between lifetime and the device fabrication time. The contact angle of the ITO substrates stored the chamber under vacuum were used to evaluate chamber cleanliness. Liquid chromatography-mass spectrometry was performed on Si wafers stored in the vacuum chamber before device fabrication to examine the impurities in the chamber. Surprisingly, despite the chamber and evaporation sources being at room temperature, a variety of materials were detected, including previously deposited materials and plasticizers from the vacuum chamber components. We show that the impurities, and not differences in water content, in the chamber were the source of lifetime variations even when the duration of exposure to impurities only varied before and after deposition of the emitter layer. These results suggest that the impurities floating in the vacuum chamber significantly impact lifetime values and reproducibility.. |
| 521. | Toshinori Matsushima, Fabrice Mathevet, Benoit Heinrich, Shinobu Terakawa, Takashi Fujihara, Chuanjiang Qin, Atula S. D. Sandanayaka, Jean-Charles Ribierre, Chihaya Adachi, N-channel field-effect transistors with an organic-inorganic layered perovskite semiconductor, APPLIED PHYSICS LETTERS, 10.1063/1.4972404, 109, 25, 2016.12, Large electron injection barriers and electrode degradation are serious issues that need to be overcome to obtain n-channel operation in field-effect transistors with an organic-inorganic layered perovskite (C6H5C2H4NH3)(2)SnI4 semiconductor. By employing low-work-function Al source/drain electrodes and by inserting C-60 layers between the perovskite semiconductor and the Al electrodes to reduce the injection barrier and to suppress the electrode degradation, we demonstrate n-channel perovskite transistors with electron mobilities of up to 2.1 cm(2)/V s, the highest value ever reported in spin-coated perovskite transistors. The n-channel transport properties of these transistors are relatively stable in vacuum but are very sensitive to oxygen, which works as electron traps in perovskite and C-60 layers. In addition, grazing-incidence X-ray scattering and thermally stimulated current measurements revealed that crystallite size and electron traps largely affect the n-channel transport properties. Published by AIP Publishing.. |
| 522. | Matsushima Toshinori, Yasuda Takeshi, Fujita Katsuhiko, Adachi Chihaya, Field-effect transistors with vacuum-deposited organic-inorganic perovskite films as semiconductor channels, JOURNAL OF APPLIED PHYSICS, 10.1063/1.4972226, 120, 23, 2016.12. |
| 523. | Hiroshi Fujimoto, Masayuki Yahiro, Satoshi Yukiwaki, Keiko Kusuhara, Nozomi Nakamura, Takashi Suekane, Hong Wei, Katsuya Imanishi, Ko Inada, Chihaya Adachi, Influence of material impurities in the hole-blocking layer on the lifetime of organic light-emitting diodes, APPLIED PHYSICS LETTERS, 10.1063/1.4972055, 109, 24, 2016.12, We evaluated the influence of impurities in an organic material used for the fabrication of organic light-emitting diodes (OLEDs) on the lifetime of the fabricated devices. Despite no differences in the current-density-voltage characteristics and external quantum efficiencies of the devices, the lifetime was approximately nine times longer for devices with high-purity 2,4,6-tris(biphenyl-3-yl)-1,3,5-triazine (T2T), which was used as a hole-block layer. Chlorine-containing impurities derived from T2T had the greatest influence on the lifetime of the OLEDs even though the amount of halogen in the source material was at most 0.9 ppm. On the other hand, the lifetime was not greatly influenced by other impurities even with concentrations up to 0.2%. Therefore, the purities of materials other than the emitter must also be closely controlled. Published by AIP Publishing.. |
| 524. | Yuya Tanaka, Takehiro Takahashi, Junichi Nishide, Yasuhide Hiraga, Hajime Nakanotani, Chihaya Adachi, Application of wide-energy-gap material 3,4-di(9H-carbazol-9-yl)benzonitrile in organic light-emitting diodes, THIN SOLID FILMS, 10.1016/j.tsf.2016.11.016, 619, 120-124, 2016.11, A material with a wide energy gap, 3,4-di(9H-carbazol-9-yl) benzonitrile (2CzBN), was synthesized and applied in organic light-emitting diodes (OLEDs). Pure blue electroluminescence with a peak wavelength of 436 nm and Commission Internationale de l'Eclairage (CIE) coordinate of (0.160, 0.084) were obtained for an OLED containing 2CzBN as an emitter, although its external emission efficiency was limited to around 1% because of the lack of thermally activated delayed fluorescence (TADF) activity. In contrast, a highly efficient TADF-based OLED was obtained when 2CzBN was used as a host instead of an emitter by taking advantage of the high triplet energy (2.92 eV) and unexpected electron transport capability of 2CzBN. (C) 2016 Elsevier B.V. All rights reserved.. |
| 525. | Sunbin Hwang, William J. Potscavage, Yu Seok Yang, In Seob Park, Toshinori Matsushima, Chihaya Adachi, Solution-processed organic thermoelectric materials exhibiting doping-concentration-dependent polarity, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 10.1039/c6cp04572c, 18, 42, 29199-29207, 2016.11, Recent progress in conducting polymer-based organic thermoelectric generators (OTEGs) has resulted in high performance due to high Seebeck coefficient, high electrical conductivity (sigma), and low thermal conductivity obtained by chemically controlling the materials's redox levels. In addition to improving the properties of individual OTEGs to obtain high performance, the development of solution processes for the fabrication of OTEG modules is necessary to realize large thermoelectric voltage and low-cost mass production. However, the scarcity of good candidates for soluble organic n-type materials limits the use of pi-leg module structures consisting of complementary elements of p- and n-type materials because of unbalanced transport coefficients that lead to power losses. In particular, the extremely low s of n-type materials compared with that of p-type materials is a serious challenge. In this study, poly(pyridinium phenylene) (P(PymPh)) was tested as an n-type semiconductor in solution-processed OTEGs, and the carrier density was controlled by a solution-based chemical doping process using the dopant sodium naphthalenide, a well-known reductant. The electronic structures and doping mechanism of P( PymPh) were explored based on the changes in UV-Vis-IR absorption, ultraviolet photoelectron, and X-ray photoelectron spectra. By controlling the dopant concentration, we demonstrate a maximum n-type power factor of 0.81 mu W m(-1) K-2 with high s, and at higher doping concentrations, a switch from n-type to p-type TE operation. This is one of the first cases of a switch in polarity just by increasing the concentration of the reductant and may open a new route for simplified fabrication of complementary organic layers.. |
| 526. | Ryoichi Ishimatsu, Yuko Kirino, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Quenching Behavior of Thermally Activated Delayed Fluorescence from a Donor-Acceptor Molecule, 1,2,3,5-Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene by O-2, CHEMISTRY LETTERS, 10.1246/cl.160561, 45, 10, 1183-1185, 2016.10, We describe the quenching behavior of thermally activated delayed fluorescence (TADF) from 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) by O-2 in bis(2-ethylhexypsebacate (DOS). Importantly, the high quantum yield of photoluminescence (phi(PL) = 0.93) with efficient TADF was dramatically decreased by O-2. The quenching rate constants of the S-1 and T-1 states were estimated to be in the order of 10(9) and 10(8) s(-1)M(-1), respectively. A DOS-plasticized polystyrene film containing 4CzIPN was prepared for optical O-2 sensing to determine O-2 concentration.. |
| 527. | Lin-Song Cui, Ya-Li Deng, Daniel Ping-Kuen Tsang, Zuo-Quan Jiang, Qisheng Zhang, Liang-Sheng Liao, Chihaya Adachi, Controlling Synergistic Oxidation Processes for Efficient and Stable Blue Thermally Activated Delayed Fluorescence Devices, ADVANCED MATERIALS, 10.1002/adma.201602127, 28, 35, 7620-+, 2016.09, Efficient sky-blue organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) display a three orders of magnitude increase in lifetime, which is superior to those of controlled phosphorescent OLEDs used in this study. The combination of electro-oxidation and photo-oxidation of the TADF emitters in their triplet excited-states is suppressed through molecule design and device engineering.. |
| 528. | Gabor Mehes, Chengjun Pan, Fatima Bencheikh, Li Zhao, Kazunori Sugiyasu, Masayuki Takeuchi, Jean-Charles Ribierre, Chihaya Adachi, Enhanced Electroluminescence from a Thiophene-Based Insulated Molecular Wire, ACS MACRO LETTERS, 10.1021/acsmacrolett.6b00205, 5, 7, 781-785, 2016.07, We report on the realization of polymer light-emitting diodes (PLEDs) based on fluorescent polythiophene (PT)-based insulated molecular wires (IMWs). PLEDs using PT emitting layers traditionally have low external quantum efficiencies (eta(eqe)) below 0.1%. Moreover, IMWs lack a thorough exploitation for electroluminescent applications due to concerns about reduced charge transport between their chains. We constructed multilayer PLEDs containing PT IMW emitting layers that show the maximum eta(eqe) close to 1.4%, luminance at 3700 cd/m(2), and low turn on voltage at 2.5 V. We also show a strong influence of the thickness of electron transport layer on eta(eqe) through device optimization and optical simulations.. |
| 529. | Nobuhiro Yanai; Mariko Kozue; Shogo Amemori; Ryota Kabe; Chihaya Adachi; Nobuo Kimizuka, Increased Vis-to-UV upconversion performance by energy level matching between a TADF donor and high triplet energy acceptors, J. Mater. Chem. C, 10.1039/C6TC01816E, 4, 27, 6447-6451, 2016.05. |
| 530. | Takeshi Komino, Yuta Sagara, Hiroyuki Tanaka, Yuji Oki, Nozomi Nakamura, Hiroshi Fujimoto, Chihaya Adachi, Electroluminescence from completely horizontally oriented dye molecules, APPLIED PHYSICS LETTERS, 10.1063/1.4954163, 108, 24, 2016.06, A complete horizontal molecular orientation of a linear-shaped thermally activated delayed fluorescent guest emitter 2,6-bis(4-(10Hphenoxazin-10-yl)phenyl)benzo[1,2-d:5,4-d'] bis(oxazole) (cis-BOX2) was obtained in a glassy host matrix by vapor deposition. The orientational order of cis-BOX2 depended on the combination of deposition temperature and the type of host matrix. Complete horizontal orientation was obtained when a thin film with cis-BOX2 doped in a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) host matrix was fabricated at 200 K. The ultimate orientation of guest molecules originates from not only the kinetic relaxation but also the kinetic stability of the deposited guest molecules on the film surface during film growth. Utilizing the ultimate orientation, a highly efficient organic light-emitting diode with the external quantum efficiency of 33.4+/-2.0% was realized. The thermal stability of the horizontal orientation of cis-BOX2 was governed by the glass transition temperature (T-g) of the CBP host matrix; the horizontal orientation was stable unless the film was annealed above T-g. Published by AIP Publishing.. |
| 531. | Atula S. D. Sandanayaka, Li Zhao, Delphine Pitrat, Jean-Christophe Mulatier, Toshinori Matsushima, Chantal Andraud, Ju-Hyung Kim, Jean-Charles Ribierre, Chihaya Adachi, Improvement of the quasi-continuous-wave lasing properties in organic semiconductor lasers using oxygen as triplet quencher, APPLIED PHYSICS LETTERS, 10.1063/1.4952970, 108, 22, 2016.05, We demonstrate quasi-continuous-wave lasing in solvent-free liquid organic semiconductor distributed feedback lasers based on a blend containing a liquid 9-(2-ethylhexyl)carbazole host doped with a blue-emitting heptafluorene derivative. The liquid gain medium is bubbled with either oxygen or nitrogen in order to investigate the role of a triplet quencher such as molecular oxygen on the quasi-continuous-wave lasing properties of organic semiconductor lasers. The oxygenated laser device exhibits a low threshold of 2 mu J cm(-2), which is lower than that measured in the nitrogenated device and is independent of the repetition rate in a range between 0.01 and 4 MHz. Published by AIP Publishing.. |
| 532. | Hiroya Arai, Hajime Nakanotani, Kei Morimoto, Chihaya Adachi, Magnesium-gold binary alloy for organic light-emitting diodes with high corrosion resistance, JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B, 10.1116/1.4952408, 34, 4, 2016.07, The authors demonstrate a simple approach to obtain cathodes that have a high resistance against corrosion by water and oxygen and an air-stable work-function of similar to 3.7 eV by doping 10 at. % of gold (Au) into a magnesium (Mg) base metal layer. Organic light-emitting diodes (OLEDs) with the Mg-Au cathodes achieved electroluminescence characteristics that are comparable to those of devices with conventional cathodes such as aluminum (Al) and Mg-silver (Ag). Although OLEDs with Al or Mg-Ag cathodes exhibited a significant reduction of their emissive area when operated in air, the emissive area of the OLEDs with Mg-Au cathodes decreased only 10% after 10 days of operation in ambient air without any specific encapsulation. These results suggest that Mg-Au cathodes can loosen the strict requirements for encapsulation, reducing the number of process steps and cost of OLED fabrication. (C) 2016 American Vacuum Society.. |
| 533. | Satoshi Watanabe, Takuma Fujita, Jean-Charles Ribierre, Kazuto Takaishi, Tsuyoshi Muto, Chihaya Adachi, Masanobu Uchiyama, Tetsuya Aoyama, Mutsuyoshi Matsumoto, Microcrystallization of a Solution-Processable Organic Semiconductor in Capillaries for High-Performance Ambipolar Field Effect Transistors, ACS APPLIED MATERIALS & INTERFACES, 10.1021/acsami.5b12713, 8, 27, 17574-17582, 2016.07, We report on the use of microcrystallization in capillaries to fabricate patterned crystalline microstructures of the low-bandgap ambipolar quinoidal quaterthiophene derivative (QQT(CN)(4)) from a chloroform solution. Aligned needle -shaped QQT(CN)(4) crystals were formed in thin film microstructures using either open-or closed capillaries made of polydimethylsiloxane (PDMS). Their charge transport properties were evaluated in a bottom-gate top-contact 10(-5) transistor configuration. Hole and electron mobilities were found to be as high as 0.17 and 0.083 cm(2) V-1 s(-1), respectively, approaching the values previously obtained in individual QQT(CN)(4) single crystal microneedles. It was possible to control the size of the needle crystals and the microline arrays by adjusting the structure of the PDMS mold and the concentration of QQT(CN)(4) solution. These results demonstrate that the microcrystallization in capillaries technique can be used to simultaneously pattern organic needle single crystals and control the microcrystallization processes. Such a simple and versatile method should be promising for the future development of high-performance organic electronic devices.. |
| 534. | NIWA Akitsugu, TAKAKI Kensho, KOBAYASHI Takashi, NAGASE Takashi, GOUSHI Kenichi, ADACHI Chihaya, NAITO Hiroyoshi, Photoluminescence in a Thermally Activated Delayed Fluorescence Emitter for Organic Light-emitting Diodes (ICAI論文特集), 日本画像学会誌, 10.11370/isj.55.143, 55, 2, 143-148, 2016.04, Thermally activated delayed fluorescence (TADF) has attracted much attention for realization of highly-efficient and low-cost organic light emitting diodes (OLEDs). OLEDs based on 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), which is one of highly-efficient TADF emitters, have been demonstrated to exhibit external quantum efficiency more than 19%. To study the decay rates from excited states of 4CzIPN, the temperature dependence of photoluminescence quantum efficiency (PLQE) has been measured in the weak photoexcitation limit in 4CzIPN-doped 1,3-bis(9-carbazolyl)benzene thin films. Characteristic features of the temperature dependence of PLQE in the weak photoexcitation limit are found, and examined by using rate equations of singlet and triplet densities.. |
| 535. | Shuho Tanimoto, Takatsugu Suzuki, Hajime Nakanotani, Chihaya Adachi, Thermally Activated Delayed Fluorescence from Pentacarbazorylbenzonitrile, CHEMISTRY LETTERS, 10.1246/cl.160290, 45, 7, 770-772, 2016.07, A benzonitrile derivative substituted by five carbazoles (5CzBN), which emits thermally activated delayed fluorescence (TADF), was synthesized and evaluated. The organic light-emitting diode (OLED) containing 5CzBN demonstrated light-blue electro-luminescence and a high external quantum efficiency of 14.8%.. |
| 536. | Jinfeng Zhang, Wencheng Chen, Sergii Kalytchuk, King Fai Li, Rui Chen, Chihaya Adachi, Zhan Chen, Andrey L. Rogach, Guangyu Zhu, Peter K. N. Yu, Wenjun Zhang, Kok Wai Cheah, Xiaohong Zhang, Chun-Sing Lee, Self-Assembly of Electron Donor-Acceptor-Based Carbazole Derivatives: Novel Fluorescent Organic Nanoprobes for Both One- and Two-Photon Cellular Imaging, ACS APPLIED MATERIALS & INTERFACES, 10.1021/acsami.6b03259, 8, 18, 11355-11365, 2016.05, In this study, we report fluorescent organic nanoprobes with intense blue, green, and orange-red emissions prepared by self-assembling three carbazole derivatives into nanorods/nanoparticles. The three compounds consist of two or four electron-donating carbazole groups linked to a central dicyanobenzene electron acceptor. Steric hindrance from the carbazole groups leads to noncoplanar 3D molecular structures favorable to fluorescence in the solid state, while the donor acceptor structures endow the molecules with good two photon excited emission properties. The fluorescent organic nanoprobes exhibit good water dispersibility, low cytotoxicity, superior resistance against photodegradation and photo bleaching. Both one- and two-photon fluorescent imaging were shown in the A549 cell line. Two-photon fluorescence imaging with the fluorescent probes was demonstrated to be more effective in visualizing and distinguishing cellular details compared to conventional one-photon fluorescence imaging.. |
| 537. | Yoshiharu Ajiki, Tetsuo Kan, Masayuki Yahiro, Akiko Hamada, Junji Adachi, Chihaya Adachi, Kiyoshi Matsumoto, Isao Shimoyama, Silicon based near infrared photodetector using self-assembled organic crystalline nano-pillars, APPLIED PHYSICS LETTERS, 10.1063/1.4945690, 108, 15, 2016.04, We propose a silicon (Si) based near-infrared photodetector using self-assembled organic crystalline nano-pillars, which were formed on an n-type Si substrate and were covered with an Au thin-film. These structures act as antennas for near-infrared light, resulting in an enhancement of the light absorption on the Au film. Because the Schottky junction is formed between the Au/n-type Si, the electron excited by the absorbed light can be detected as photocurrent. The optical measurement revealed that the nano-pillar structures enhanced the responsivity for the near-infrared light by 89 (14.5 mA/W) and 16 (0.433 mA/W) times compared with those of the photodetector without nano-pillars at the wavelengths of 1.2 and 1.3 mu m, respectively. Moreover, no polarization dependency of the responsivity was observed, and the acceptable incident angle ranged from 0 degrees to 30 degrees. These broad responses were likely to be due to the organic nano-pillar structures' having variation in their orientation, which is advantageous for near-infrared detector uses. (C) 2016 AIP Publishing LLC.. |
| 538. | Munetomo Inoue, Toshinori Matsushima, Chihaya Adachi, Low amplified spontaneous emission threshold and suppression of electroluminescence efficiency roll-off in layers doped with ter(9,9 '-spirobifluorene), APPLIED PHYSICS LETTERS, 10.1063/1.4945596, 108, 13, 2016.03, We demonstrate that ter(9,9'-spirobifluorene) (TSBF) doped in a host matrix layer of 4,4'-bis (carbazol-9-yl) biphenyl (CBP) shows a low amplified spontaneous emission (ASE) threshold (E-th = 1.0 mu J cm(-2)) and suppressed electroluminescence efficiency roll-off at high current densities (no roll-off up to 100mAcm(-2)). One origin of the low ASE threshold is that the TSBF-doped CBP layer possesses a very large radiative decay constant (k(r) = 1.1 x 10(9) s(-1)). Singlet-triplet annihilation is almost suppressed in the TSBF-doped CBP layer, which can be ascribed to the small overlap between the emission and triplet absorption of TSBF. Also, the small energy level difference between TSBF and CBP minimizes carrier trapping in TSBF, leading to the suppression of singlet-polaron annihilation. TSBF showed one of the lowest Eth and the most suppressed efficiency rolloff among organic laser dyes investigated in this study and, therefore, is believed to be a promising candidate to realize electrically pumped organic semiconductor laser diodes in the future. (C) 2016 AIP Publishing LLC.. |
| 539. | Lin-Song Cui, Jong Uk Kim, Hiroko Nomura, Hajime Nakanotani, Chihaya Adachi, Benzimidazobenzothiazole-Based Bipolar Hosts to Harvest Nearly All of the Excitons from Blue Delayed Fluorescence and Phosphorescent Organic Light-Emitting Diodes, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.201601136, 55, 24, 6864-6868, 2016.06, Much effort has been devoted to developing highly efficient organic light-emitting diodes (OLEDs) that function through phosphorescence or thermally activated delayed fluorescence (TADF). However, efficient host materials for blue TADF and phosphorescent guest emitters are limited because of their requirement of high triplet energy levels. Herein, we report the rigid acceptor unit benzimidazobenzothiazole (BID-BT), which is suitable for use in bipolar hosts in blue OLEDs. The designed host materials, based on BID-BT, possess high triplet energy and bipolar carrier transport ability. Both blue TADF and phosphorescent OLEDs containing BID-BT-based derivatives exhibit external quantum efficiencies as high as 20%, indicating that these hosts allow efficient triplet exciton confinement appropriate for blue TADF and phosphorescent guest emitters.. |
| 540. | Wada, Y, Shizu, K, Kubo, S, Fukushima, T, Miwa, T, Tanaka, H, Adachi, C, Kaji, H, 【2016-2】Highly efficient solution-processed host-free organic light-emitting diodes showing an external quantum efficiency of nearly 18% with a thermally activated delayed fluorescence emitter, Appl. Phys. Express, 10.7567/APEX.9.032102, 9, 3, [032102-1]-[032102-3], 2016.03. |
| 541. | Daniel Ping-Kuen Tsang, Chihaya Adachi, Operational stability enhancement in organic light-emitting diodes with ultrathin Liq interlayers, SCIENTIFIC REPORTS, 10.1038/srep22463, 6, 22463, 2016.03, Organic light-emitting diodes (OLEDs) under constant current operation suffer from a decrease of luminance accompanied by an increase of driving voltage. We report a way to greatly improve the stability of OLEDs having a green emitter exhibiting thermally activated delayed fluorescence (TADF), (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl) isophthalonitrile (4CzIPN), by introducing ultrathin (1 to 3 nm) interlayers of 8-hydroxyquinolinato lithium (Liq) between hole-blocking layer and its surrounding emissive and electron-transport layers. Under constant current operation starting at a luminescence of 1,000 cd/m(2), the time to reach 90% of initial luminance (LT90) increased eight times, resulting in LT90 = 1,380 hours after insertion of the interlayers. Combining this new concept and mixed host system, LT95 was further extended to 1315 hours that is 16 times of reference device. This is the best value reported for TADF-based OLEDs and is comparable to the operational lifetimes of well-established phosphorescence-based OLEDs. Thermally stimulated current measurements showed that the number of deep charge traps was reduced with the insertion of the ultrathin Liq interlayer, indicating that reducing the number of deep traps is important for improving the operational lifetime and that exciton-polaron annihilation may be a source of the device degradation.. |
| 542. | Hajime Nakanotani, Taro Furukawa, Kei Morimoto, Chihaya Adachi, Long-range coupling of electron-hole pairs in spatially separated organic donor-acceptor layers, SCIENCE ADVANCES, 10.1126/sciadv.1501470, 2, 2, e1501470, 2016.02, Understanding exciton behavior in organic semiconductor molecules is crucial for the development of organic semiconductor-based excitonic devices such as organic light-emitting diodes and organic solar cells, and the tightly bound electron-hole pair forming an exciton is normally assumed to be localized on an organic semi-conducting molecule. We report the observation of long-range coupling of electron-hole pairs in spatially separated electron-donating and electron-accepting molecules across a 10-nm-thick spacer layer. We found that the exciton energy can be tuned over 100 meV and the fraction of delayed fluorescence can be increased by adjusting the spacer-layer thickness. Furthermore, increasing the spacer-layer thickness produced an organic light-emitting diode with an electroluminescence efficiency nearly eight times higher than that of a device without a spacer layer. Our results demonstrate the first example of a long-range coupled charge-transfer state between electron-donating and electron-accepting molecules in a working device.. |
| 543. | Sae Youn Lee, Chihaya Adachi, Takuma Yasuda, High-Efficiency Blue Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence from Phenoxaphosphine and Phenoxathiin Derivatives, ADVANCED MATERIALS, 10.1002/adma.201506391, 28, 23, 4626-4631, 2016.06, High-efficiency blue thermally activated delayed fluorescence (TADF) molecules, consisting of phenoxaphosphine oxide and phenoxathiin dioxide as acceptor units and 9,9-dimethylacridan as a donor unit, are reported. Maximum external electroluminescence quantum efficiencies of up to 20.5% are achieved in blue organic light-emitting diodes (OLEDs) by employing these materials as TADF emitters.. |
| 544. | Sae Youn Lee, Takuma Yasuda, Hideaki Komiyama, Jiyoung Lee, Chihaya Adachi, Thermally Activated Delayed Fluorescence Polymers for Efficient Solution-Processed Organic Light-Emitting Diodes, ADVANCED MATERIALS, 10.1002/adma.201505026, 28, 21, 4019-4024, 2016.06, Thermally activated delayed fluorescence (TADF) pi-conjugated polymers are developed for solution-processed TADF-OLEDs. Benzophenone-based alternating donor-acceptor structures contribute to the small Delta E-ST, enabling efficient exciton-harvesting through TADF. Solution-processed OLEDs using the TADF polymers as emitters can achieve high maximum external electroluminescence efficiencies of up to 9.3%.. |
| 545. | Atula S. D. Sandanayaka, Kou Yoshida, Munetomo Inoue, Chuanjiang Qin, Kenichi Goushi, Jean-Charles Ribierre, Toshinori Matsushima, Chihaya Adachi, Quasi-Continuous-Wave Organic Thin-Film Distributed Feedback Laser, ADVANCED OPTICAL MATERIALS, 10.1002/adom.201600006, 4, 6, 834-839, 2016.06. |
| 546. | Ju-Hyung Kim, Jean-Charles Ribierre, Yu Seok Yang, Chihaya Adachi, Maki Kawai, Jaehoon Jung, Takanori Fukushima, Yousoo Kim, Seamless growth of a supramolecular carpet, NATURE COMMUNICATIONS, 10.1038/ncomms10653, 7, 10653, 2016.02, Organic/metal interfaces play crucial roles in the formation of intermolecular networks on metal surfaces and the performance of organic devices. Although their purity and uniformity have profound effects on the operation of organic devices, the formation of organic thin films with high interfacial uniformity on metal surfaces has suffered from the intrinsic limitation of molecular ordering imposed by irregular surface structures. Here we demonstrate a supramolecular carpet with widely uniform interfacial structure and high adaptability on a metal surface via a one-step process. The high uniformity is achieved with well-balanced interfacial interactions and site-specific molecular rearrangements, even on a pre-annealed amorphous gold surface. Co-existing electronic structures show selective availability corresponding to the energy region and the local position of the system. These findings provide not only a deeper insight into organic thin films with high structural integrity, but also a new way to tailor interfacial geometric and electronic structures.. |
| 547. | Kou Yoshida, Hajime Nakanotani, Chihaya Adachi, Effect of Joule heating on transient current and electroluminescence in p-i-n organic light-emitting diodes under pulsed voltage operation, ORGANIC ELECTRONICS, 10.1016/j.orgel.2016.01.039, 31, 287-294, 2016.04, The transient current and electroluminescent characteristics of p-i-n organic light-emitting diodes driven using short voltage pulses with various amplitudes and pulse widths were investigated to understand high current behavior (>10 A/cm(2)). Even under short voltage pulse operation, Joule heating was found to strongly affect the transient characteristics and lead to temperature rises estimated to be over 100 K in the high current density region (>400 A/cm(2)). This results in a large increase in both current density and EL intensity within the pulse width. In addition, the Joule heating was found to have an effect on the external quantum efficiency. However its contribution was found to be limited compared with the other quenching mechanism, singlet-polaron quenching. (C) 2016 Elsevier B.V. All rights reserved.. |
| 548. | Kou Yoshida, Toshinori Matsushima, Hajime Nakanotani, Chihaya Adachi, Quantification of temperature rise in unipolar organic conductors during short voltage-pulse excitation using electrical testing methods, ORGANIC ELECTRONICS, 10.1016/j.orgel.2016.01.033, 31, 191-197, 2016.04, To quantify the rise in device temperature caused by Joule heating during short voltage-pulse excitation at high current densities (> 10 A/cm(2)), the device temperatures of unipolar organic conductors were measured using electrical testing methods. For a maximum voltage amplitude of 59 V at a current density of similar to 300 A/cm(2), temperature rose over 145 degrees C within a pulse duration of 5 mu s in an N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (alpha-NPD)-based single-carrier organic conductor. This result is in reasonable agreement with numerically calculated values. These findings indicate that suppressing the effects of Joule heating by carefully adjusting pulse width, substrate and organic materials, and device configuration is important to achieve further carrier injection in the ultra-high current density region (> 1 kA/cm(2)). (C) 2016 Elsevier B.V. All rights reserved.. |
| 549. | Yu Esaki, Toshinori Matsushima, Chihaya Adachi, Current Enhancement in Organic Films through Gap Compression by Cold and Hot Isostatic Pressing, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.201505190, 26, 17, 2940-2949, 2016.05, The spatial gaps in organic films are compressed using cold and hot isostatic pressing (CIP and HIP, respectively) with the aim of enhancing their electrical characteristics. The microscopic gaps formed in amorphous organic films by inefficient molecular packing are difficult to compress using CIP and HIP; however, the macroscopic gaps formed between grains and other grains or substrates in polycrystalline organic films can be compressed using CIP and HIP. The gap compression by CIP and HIP in polycrystalline films enhances their electrical characteristics. Conversely, the electrical characteristics of amorphous films remain unchanged after CIP and HIP. HIP gives almost the same results as CIP in terms of gap compression and current enhancement, probably because the expected activation of molecular motion at high temperature is suppressed under high applied pressure. CIP markedly improves the performance of organic light-emitting diodes, organic solar cells, and organic field-effect transistors containing polycrystalline films. These findings are important for understanding the carrier injection and transport mechanisms of organic films containing gaps as well as enhancing the performance of future organic devices, especially those with polycrystalline films.. |
| 550. | Ryoichi Ishimatsu, Tomohiko Edura, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Photophysical Properties and Efficient, Stable, Electrogenerated Chemiluminescence of Donor-Acceptor Molecules Exhibiting Thermal Spin Upconversion, CHEMISTRY-A EUROPEAN JOURNAL, 10.1002/chem.201600077, 22, 14, 4889-4898, 2016.03, The photophysical properties and electrogenerated chemiluminescence (ECL) of three donor-acceptor molecules composed of dicyanobenzene and methyl-, tert-butyl-, and phenyl-substituted carbazolyl groups, 1,2,3,5-tetrakis(3,6-disubstituted-carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN-Me, 4CzIPN-tBu, and 4CzIPN-Ph, respectively) are described. These molecules show delayed fluorescence as a result of thermal spin upconversion from the lowest triplet state to the lowest singlet state at room temperature. The three molecules showed yellow to yellowish-red ECL. Remarkably, the ECL efficiencies of 4CzIPN-tBu in dichloromethane reached almost 40%. Moreover, stable ECL was emitted from 4CzIPN-tBu and 4CzIPN-Ph. In case of 4CzIPN-Me, the ECL intensity decreased during voltage cycles because of polymerization. Quantum chemical calculations revealed that polymerization was inhibited by the steric hindrance of the bulky tert-butyl and phenyl groups on the carbazolyl moieties and lowered the spin density on the carbazolyl groups through electron conjugation for 4CzIPN-Ph.. |
| 551. | In Seob Park, Sae Youn Lee, Chihaya Adachi, Takuma Yasuda, Full-Color Delayed Fluorescence Materials Based on Wedge-Shaped Phthalonitriles and Dicyanopyrazines: Systematic Design, Tunable Photophysical Properties, and OLED Performance, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.201505106, 26, 11, 1813-1821, 2016.03, Purely organic light-emitting materials, which can harvest both singlet and triplet excited states to offer high electron-to-photon conversion efficiencies, are essential for the realization of high-performance organic light-emitting diodes (OLEDs) without using precious metal elements. Donor-acceptor architectures with an intramolecular charge-transfer excited state have been proved to be a promising system for achieving these requirements through a mechanism of thermally activated delayed fluorescence (TADF). Here, luminescent wedge-shaped molecules, which comprise a central phthalonitrile or 2,3-dicyanopyrazine acceptor core coupled with various donor units, are reported as TADF emitters. This set of materials allows systematic fine-tuning of the band gap and exhibits TADF emissions that cover the entire visible range from blue to red. Full-color TADF-OLEDs with high maximum external electroluminescence quantum efficiencies of up to 18.9% have been demonstrated by using these phthalonitrile and 2,3-dicyanopyrazine-based TADF emitters.. |
| 552. | Sunbin Hwang, William J. Potscavage, Ryosuke Nakamichi, Chihaya Adachi, Processing and doping of thick polymer active layers for flexible organic thermoelectric modules, ORGANIC ELECTRONICS, 10.1016/j.orgel.2016.01.007, 31, 31-40, 2016.04, While the majority of research on organic thermoelectric generators has focused on individual devices with organic films having thicknesses of several hundred nanometers (nano-films), films with micrometer-scale thicknesses (micro-films) provide a longer thermal conduction path that results in a larger temperature gradient and higher thermoelectric voltages in modules. In this study, the properties of solution-processed nano-and micro-films of the p-type semiconductor P3HT doped with two different dopants, F-4-TCNQ and Fe3+-tos(3)center dot 6H(2)O, were investigated. While doping with F-4-TCNQ resulted in high electrical conductivity only in nano-films, doping with Fe3+-tos(3)center dot 6H(2)O from a 25 mM solution yielded power factors of up to similar to 30 mu Wm(-1) K-2 with a conductivity of 55.4 Scm(-1) in micro-films. Changes in the molecular packing were compared based on X-ray diffraction, and the best operational stability in air was found for the Fe3+-tos(3)center dot 6H(2)O-doped micro-films. Using Fe3+-tos(3)center dot 6H(2)O as dopant, flexible thermoelectric modules with solution-processed micro-films patterned by a photo-etching technique that does not require alignment and assembly of individual devices were demonstrated, exhibiting a maximum power output of 1.94 nWK(-2) for a uni-leg module with 48 elements. Analysis of the flexible module performance showed that the performance is limited by the contact resistance, which must be taken into consideration when optimizing module structure. (c) 2016 Elsevier B.V. All rights reserved.. |
| 553. | Munetomo Inoue, Tomas Serevicius, Hajime Nakanotani, Kou Yoshida, Toshinori Matsushima, Saulius Jursenas, Chihaya Adachi, Effect of reverse intersystem crossing rate to suppress efficiency roll-off in organic light-emitting diodes with thermally activated delayed fluorescence emitters, CHEMICAL PHYSICS LETTERS, 10.1016/j.cplett.2015.11.042, 644, 62-67, 2016.01, Electroluminescence efficiency roll-off in organic light-emitting diodes with thermally activated delayed fluorescence emitters 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN) and 3-(9,9-dimethylacridin-10(9H)-yl)-9H-xanthen-9-one (ACRXTN) is investigated by considering intramolecular exciton relaxation processes. Electroluminescence efficiency roll-off at high current density is dramatically suppressed using ACRXTN as an emitter instead of 2CzPN because of suppressed bimolecular exciton annihilation processes such as singlet-triplet and triplet-triplet annihilation. The rate constant of reverse intersystem crossing from triplet to singlet excited states of ACRXTN is about 300 times higher than that of 2CzPN, decreasing triplet exciton density and suppressing exciton annihilation processes under optical and electrical excitation. (C) 2015 Elsevier B.V. All rights reserved.. |
| 554. | Chuanjiang Qin, Toshinori Matsushima, Takashi Fujihara, William J. Potscavage, Chihaya Adachi, Degradation Mechanisms of Solution-Processed Planar Perovskite Solar Cells: Thermally Stimulated Current Measurement for Analysis of Carrier Traps, ADVANCED MATERIALS, 10.1002/adma.201502610, 28, 3, 466-471, 2016.01, Degradation mechanisms of CH3NH3PbI3-based planar perovskite solar cells (PSCs) are investigated using a thermally stimulated current technique. Hole traps lying above the valence-band edge of the CH3NH3PbI3 are detected in PSCs degraded by continuous simulated solar illumination. One source of the hole traps is the photo-degradation of CH3NH3PbI3 in the presence of water.. |
| 555. | Ryota Kabe, Naoto Notsuka, Kou Yoshida, Chihaya Adachi, Afterglow Organic Light-Emitting Diode, ADVANCED MATERIALS, 10.1002/adma.201504321, 28, 4, 655-660, 2016.01, An afterglow organic light-emitting diode (OLED) that displays electroluminescence with long transient decay after it is turned off is demonstrated. This OLED exhibits blue and green dual emission originating from fluorescence and phosphorescence, respectively. A phosphorescence lifetime of 4.3 s is achieved.. |
| 556. | Hiroshi Fujimoto, Masayuki Yahiro, Takayuki Kawashima, Keisuke Konno, Qiang Chen, Kunio Sawaya, Shojiro Kawakami, Chihaya Adachi, Improvement in the light outcoupling efficiency of organic light-emitting diodes using a hemispherical lens and a multipatterned one-dimensional photonic crystal fabricated by autocloning, APPLIED PHYSICS EXPRESS, 10.7567/APEX.8.082102, 8, 8, 2015.08, The outcoupling efficiency of organic light-emitting diodes was improved using a photonic crystal fabricated by autocloning, which has potential advantages for mass production. By using layer thicknesses optimized by optical simulations, the experimental external quantum efficiency of a device with the photonic crystal and a hemispherical lens was 43.4%, which is 2.13 times that of a device on a flat substrate without the lens. Comparisons with the simulated distributions of the light modes in the devices show that the photonic crystal reduces the light loss from the waveguide and evanescent modes. The emission pattern was independent of substrate rotation. (C) 2015 The Japan Society of Applied Physics. |
| 557. | Yasuhide Hiraga, Jun-ichi Nishide, Hajime Nakanotani, Masaki Aonuma, Chihaya Adachi, High-Efficiency Sky-Blue Organic Light-Emitting Diodes Utilizing Thermally-Activated Delayed Fluorescence, IEICE TRANSACTIONS ON ELECTRONICS, 10.1587/transele.E98.C.971, E98C, 10, 971-976, 2015.10, A highly efficient sky-blue organic light-emitting diode (OLED) based on a thermally-activated delayed fluorescence (TADF) molecule, 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN), was studied. The sky-blue OLED exhibited a maximum external electroluminescence quantum efficiency (eta(EQE)) of over 24.0%. In addition, a white OLED using 2CzPN combined with green and orange TADF emitters showed a high eta(EQE) of 17.3% with a maximum power efficiency of 52.3 lm/W and Commission Internationale de l'Eclairage coordinates of (0.32, 0.43).. |
| 558. | Li Zhao, Munetomo Inoue, Kou Yoshida, Atula S. D. Sandanayaka, Ju-Hyung Kim, Jean-Charles Ribierre, Chihaya Adachi, Singlet-Triplet Exciton Annihilation Nearly Suppressed in Organic Semiconductor Laser Materials Using Oxygen as a Triplet Quencher, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, 10.1109/JSTQE.2015.2473138, 22, 1, 34, 2016.01, We report on the use of oxygen as triplet quencher to reduce singlet-triplet annihilation in light-emitting organic solid films and solvent-free molecular semiconducting liquids. For this purpose, a fluorescent heptafluorene derivative is dispersed either in a wide bandgap 4,4'-Bis (N-carbazolyl)-1,1'-biphenyl (CBP) host or in a solvent-free liquid matrix based on 9-(2-ethylhexyl) carbazole (EHCz). To introduce oxygen in the samples, a modified cold isostatic pressure technique is used in the case of spin-coated CBP blends while oxygen is bubbled in the liquids. The influence of the oxygenation on their photophysical and amplified spontaneous emission properties is examined. Both solid blend films and liquids showed before and after the introduction of oxygen a photoluminescence quantum yield higher than 80% and an amplified spontaneous emission threshold lower than 0.4 mu J/cm(2). While oxygen does not quench significantly the singlet excitons in these systems, singlet-triplet annihilation is strongly reduced in solid thin films and nearly suppressed in the liquid layers. This study demonstrates that liquid organic semiconductors are promising candidates for optically pumped continuous wave lasers and provides important insights for a more effective triplet management in organic semiconductor lasers.. |
| 559. | Atula S. D. Sandanayaka, Toshinori Matsushima, Chihaya Adachi, Degradation Mechanisms of Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence Molecules, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/acs.jpcc.5b07084, 119, 42, 23845-23851, 2015.10, Degradation of organic light-emitting diodes (OLEDs) operated continuously at a constant current density is investigated using photoluminescence techniques. The OLEDs contained the thermally activated delayed fluorescence emitting dopant (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN). OLED degradation proceeds mainly on the basis of excited-state instability of host molecules rather than processes related to 4CzIPN. Additionally, the electrochemical instability of radical cations and anions influences long-term OLED degradation. The formation of exciton quenchers and nonradiative carrier recombination centers acts to reduce OLED luminance. These findings highlight the need for new host material development to fabricate more stable TADF-OLEDs.. |
| 560. | Jinfeng Zhang, Rui Chen, Zelin Zhu, Chihaya Adachi, Xiaohong Zhang, Chun-Sing Lee, Highly Stable Near-Infrared Fluorescent Organic Nanoparticles with a Large Stokes Shift for Noninvasive Long-Term Cellular Imaging, ACS APPLIED MATERIALS & INTERFACES, 10.1021/acsami.5b08539, 7, 47, 26266-26274, 2015.12, Fluorescent organic nanoparticles based on small molecules have been regarded as promising candidates for bioimaging in recent years. In this study, we report a highly stable near-infrared (NIR) fluorescent organic nanoprobes based on nanoparticles of an anthraquinone derivate with strong aggregation-induced emission (AIR) characteristics and a large Stokes shift (>175 nm). These endow the nanoprobe with high fluorescent brightness and high signal-to-noise ratio. On the other hand, the nanoprobe also shows low cytotoxicity, good stability over a wide pH range, superior resistance against photodegradation and photobleaching comparing to typical commercial fluorescent organic dyes such as fluorescein sodium. Endowed with such merits in term of optical performance, biocompatibility, and stability, the nanoprobe is demonstrated to be an ideal fluorescent probe for noninvasive long-term cellular tracing and imaging applications. As an example, it is shown that strong red fluorescence from the nanoprobe can still be clearly observed in A549 human lung cancer cells after incubation for six generations over 15 days.. |
| 561. | Hironori Kaji, Hajime Suzuki, Tatsuya Fukushima, Katsuyuki Shizu, Katsuaki Suzuki, Shosei Kubo, Takeshi Komino, Hajime Oiwa, Furitsu Suzuki, Atsushi Wakamiya, Yasujiro Murata, Chihaya Adachi, Purely organic electroluminescent material realizing 100% conversion from electricity to light, NATURE COMMUNICATIONS, 10.1038/ncomms9476, 6, 8476, 2015.10, Efficient organic light-emitting diodes have been developed using emitters containing rare metals, such as platinum and iridium complexes. However, there is an urgent need to develop emitters composed of more abundant materials. Here we show a thermally activated delayed fluorescence material for organic light-emitting diodes, which realizes both approximately 100% photoluminescence quantum yield and approximately 100% up-conversion of the triplet to singlet excited state. The material contains electron-donating diphenylamin-ocarbazole and electron-accepting triphenyltriazine moieties. The typical trade-off between effective emission and triplet-to-singlet up-conversion is overcome by fine-tuning the highest occupied molecular orbital and lowest unoccupied molecular orbital distributions. The nearly zero singlet-triplet energy gap, smaller than the thermal energy at room temperature, results in an organic light-emitting diode with external quantum efficiency of 29.6%. An external quantum efficiency of 41.5% is obtained when using an out-coupling sheet. The external quantum efficiency is 30.7% even at a high luminance of 3,000 cdm(-2).. |
| 562. | Katsuyuki Shizu, Hiroki Noda, Hiroyuki Tanaka, Masatsugu Taneda, Motoyuki Uejima, Tohru Sato, Kazuyoshi Tanaka, Hironori Kaji, Chihaya Adachi, Highly Efficient Blue Electroluminescence Using Delayed-Fluorescence Emitters with Large Overlap Density between Luminescent and Ground States, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/acs.jpcc.5b07798, 119, 47, 26283-26289, 2015.11, The use of thermally activated delayed-fluorescence (TADF) allows the realization of highly efficient organic light-emitting diodes (OLEDs) and is a promising alternative to the use of conventional fluorescence and phosphorescence. Recent research interest has focused on blue TADF emitters. In this study, we use quantum mechanics to reveal the relationship between the molecular structures and the photophysical properties of TADF emitters and derive a direction for the molecular design of highly efficient blue TADF emitters. Theoretical analyses show that the luminescence efficiency of TADF emitters largely depends on the overlap density (rho(10)) between the electronic wave functions of the ground state and the lowest excited singlet state. By increasing rho(10), we develop an efficient sky-blue TADF emitter material, 9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9'-phenyl-9H,9'H-3,3'-bicarbazole (BCzT). When doped into a host layer, BCzT produces a high photoluminescence quantum yield of 95.6%. From the transient photoluminescence decays of the doped film, the efficiency of excited triplet state conversion into light is estimated to be 76.2%. An OLED using BCzT as a sky-blue emitter produces a maximum external quantum efficiency (EQE) of 21.7%, which is much higher than the EQE range of conventional fluorescent OLEDs (57.5%). The high EQE is a result of the high triplet-to-light conversion efficiency of BCzT. Our material design based on rho(10) distribution provides a rational approach for developing TADF emitters for high-efficiency blue OLEDs.. |
| 563. | Toshiya Yonehara, Kenichi Goushi, Tomoaki Sawabe, Isao Takasu, Chihaya Adachi, Comparison of transient state and steady state exciton-exciton annihilation rates based on Forster-type energy transfer, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.7567/JJAP.54.071601, 54, 7, 2015.07, We investigated differences between the transient state and steady state exciton-exciton annihilation rates based on Forster-type energy transfer. The exciton-exciton annihilation rate of an organic semiconductor is usually determined by transient state photoluminescence measurements using a pulsed laser or steady state photoluminescence measurements using a continuous wave laser. However, it is unclear that the respective annihilation rates determined by their rate equations are the same. In calculations with platinum-octaethylporphyrin (PtOEP) parameters, Monte Carlo simulations gave two different annihilation rates for the transient state and the steady state. The analytical models based on Forster-type energy transfer also showed the same result. These results indicate that the exciton-exciton annihilation rates in transient state and steady state are distinguished. (C) 2015 The Japan Society of Applied Physics. |
| 564. | Hiroyuki Kuwae, Atsushi Nitta, Kou Yoshida, Takashi Kasahara, Toshinori Matsushima, Munetomo Inoue, Shuichi Shoji, Jun Mizuno, Chihaya Adachi, Suppression of external quantum efficiency roll-off of nanopatterned organic-light emitting diodes at high current densities, JOURNAL OF APPLIED PHYSICS, 10.1063/1.4932139, 118, 15, 2015.10, We developed organic light-emitting diodes (OLEDs) with nanopatterned current flow regions using electron-beam lithography with the aim of suppressing singlet-polaron annihilation (SPA). Nanopatterns composed of lines and circles were used in the current flow regions of nano-line and nano-dot OLEDs, respectively. Excitons partially escape from the current flow regions where SPA takes place. As such, current densities where external quantum efficiencies were half of their initial values (J(0)) increased as line width and circle diameter were decreased to close to the exciton diffusion length. Circles were more efficient at enhancing exciton escape and increasing J(0) than lines. The J(0) increase in the nano-dot OLEDs containing nanopatterned circles with a diameter of 50 nm was approximately 41-fold that of a conventional OLED with a current flow region of 4 mm(2). The dependence of J(0) on the size and shape of the nanopatterns was well explained by an SPA model that considered exciton diffusion. Nanopatterning of OLEDs is a feasible method of obtaining large J(0). (C) 2015 AIP Publishing LLC.. |
| 565. | Toshinori Matsushima, Atula S. D. Sandanayaka, Yu Esaki, Chihaya Adachi, Vacuum-and-solvent-free fabrication of organic semiconductor layers for field-effect transistors, SCIENTIFIC REPORTS, 10.1038/srep14547, 5, 14547, 2015.09, We demonstrate that cold and hot isostatic pressing (CIP and HIP) is a novel, alternative method for organic semiconductor layer fabrication, where organic powder is compressed into a layer shape directly on a substrate with 200 MPa pressure. Spatial gaps between powder particles and the other particles, substrates, or electrodes are crushed after CIP and HIP, making it possible to operate organic field-effect transistors (OFETs) containing the compressed powder as the semiconductor. The CIP-compressed powder of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) had a hole mobility of (1.6 +/- 0.4) x 10(-2) cm(2)/Vs. HIP of C8-BTBT powder increased the hole mobility to an amorphous silicon-like value (0.22 +/- 0.07 cm(2)/Vs) because of the growth of the C8-BTBT crystallites and the improved continuity between the powder particles. The vacuum and solution processes are not involved in our CIP and HIP techniques, offering a possibility of manufacturing OFETs at low cost.. |
| 566. | Yan-Qiong Zheng, Jing Zhang, Fang Yang, Takeshi Komino, Bin Wei, Jianhua Zhang, Zixing Wang, Wenhong Pu, Changzhu Yang, Chihaya Adachi, Influence of deposition substrate temperature on the morphology and molecular orientation of chloroaluminum phthalocyanine films as well the performance of organic photovoltaic cells, NANOTECHNOLOGY, 10.1088/0957-4484/26/40/405202, 26, 40, 405202, 2015.10, The dependence of the morphology of neat chloroaluminum phthalocyanine (ClAlPc) films on substrate temperature (T-sub) during deposition is investigated by variable angle spectroscopic ellipsometry (VASE), x-ray diffraction (XRD), and atomic force microscopy (AFM) to obtain detailed information about the molecular orientation, phase separation, and crystallinity. AFM images indicate that both grain size and root mean square (RMS) roughness noticeably increase with T-sub both in neat and blend films. Increasing T-sub from room temperature to 420 K increases the horizontal orientation of the ClAlPc molecules with an increase of the mean molecular tilt angle from 60.13 degrees (300 K) to 65.86 degrees (420 K). The UV-vis absorption band of the corresponding films increases and the peak wavelength slightly red shifts with the T-sub increase. XRD patterns show a clear diffraction peak at T-sub over 390 K, implying the p-stacking of interconnected ClAlPc molecules at high T-sub. Planar and bulk heterojunction (BHJ) photovoltaic cells containing pristine ClAlPc films and ClAlPc: C-60 blend films fabricated at T-sub of 390 K show increases in the power conversion efficiency (eta(PCE)) of 28% (eta(PCE) = 3.12%) and 36% (eta(PCE) = 3.58%), respectively, relative to devices as-deposited at room temperature. The maximum short circuit current in BHJs is obtained at 390 K in the T-sub range from 300 K to 450 K.. |
| 567. | Tatsuya Fukushima, Junichi Yamamoto, Masashi Fukuchi, Shuzo Hirata, Heo Hyo Jung, Osamu Hirata, Yuki Shibano, Chihaya Adachi, Hironori Kaji, Material degradation of liquid organic semiconductors analyzed by nuclear magnetic resonance spectroscopy, AIP ADVANCES, 10.1063/1.4928515, 5, 8, 2015.08, Liquid organic light-emitting diodes (liquid OLEDs) are unique devices consisting only of liquid organic semiconductors in the active layer, and the device performances have been investigated recently. However, the device degradation, especially, the origin has been unknown. In this study, we show that material degradation occurs in liquid OLEDs, whose active layer is composed of carbazole with an ethylene glycol chain. Nuclear magnetic resonance (NMR) experiments clearly exhibit that the dimerization reaction of carbazole moiety occurs in the liquid OLEDs during driving the devices. In contrast, cleavages of the ethylene glycol chain are not detected within experimental error. The dimerization reaction is considered to be related to the device degradation. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.. |
| 568. | Toshinori Matsushima; Takashi Fujihara; Chuanjiang Qin; Shinobu Terakawa; Yu Esaki; Sunbin Hwang; Atula S. D. Sandanayaka; William J. Potscavage, Jr.; Chihaya Adachi, Morphological control of organic-inorganic perovskite layers by hot isostatic pressing for efficient planar solar cells, J. Mater. Chem. A, 10.1039/C5TA03796D, 3, 17780-17787, 2015.07. |
| 569. | Hirofumi Nakamura, Seong-Hee Noh, Miki Kuribayashi, Chihaya Adachi, Influence of the atmosphere on organic-organic interfacial layers and deterioration in organic light-emitting diodes, JOURNAL OF THE SOCIETY FOR INFORMATION DISPLAY, 10.1002/jsid.318, 23, 3, 129-137, 2015.03, The influence of organic-organic interfacial contaminants and deterioration in organic light-emitting diodes (OLEDs) was investigated. There was deterioration of the device characteristics when atmospheric contamination was introduced to the emission site. We simultaneously observed a decrease of the maximum capacitance, C-max, of the OLEDs, implying that there was charge accumulation at the interface. Our study demonstrates that maintaining the interface adjacent to emission site free from contaminants is crucial to protect the device from deterioration.. |
| 570. | Tomohiko EDURA, Kohei TSUGITA, Chihaya ADACHI, Large-Area Deposition Technology of High Purity Organic Thin Film by Gas Flow Deposition, Journal of the Vacuum Society of Japan, 10.3131/jvsj2.58.79, 58, 3, 79-85, 2015.05. |
| 571. | Myung Eun Jang, Takuma Yasuda, Jiyoung Lee, Sae Youn Lee, Chihaya Adachi, Organic Light-emitting Diodes Based on Donor-substituted Phthalimide and Maleimide Fluorophores, CHEMISTRY LETTERS, 10.1246/cl.150454, 44, 9, 1248-1250, 2015.09, Highly luminescent phthalimide- and maleimide-based molecules having donor acceptor donor electronic configurations have been developed. A phthalimide-based material exhibited highly efficient green delayed fluorescence owing to its small singlet triplet energy gap. An organic light-emitting diode using the molecules as an emitter exhibited a high maximum external electroluminescence quantum efficiency of 11.5%, which exceeds those obtained with common fluorescent emitters.. |
| 572. | Hajime Nakanotani, Taro Furukawa, Chihaya Adachi, Light Amplification in an Organic Solid-State Film with the Aid of Triplet-to-Singlet Upconversion, ADVANCED OPTICAL MATERIALS, 10.1002/adom.201500236, 3, 10, 1381-1388, 2015.10, Organic laser dyes can be optically excited to achieve light amplification. The buildup of an excessive population of triplets is generally believed to limit the duration of the light amplification because of optical losses through excited-state absorption, so triplet excitons are usually eliminated by using a triplet quencher. However, destroying the triplets limits the electroluminescence efficiency of organic materials under electrical pumping and is counterproductive to realizing electrically pumped organic laser devices. Herein, light amplification is reported which constructively uses triplet states in an optically pumped organic film. In this system, the triplets are converted into singlets by reverse intersystem crossing in a "triplet harvester," and then the singlets are resonantly transferred to the singlet state of the laser dye. Since this approach permits the constructive use of triplets, not only gain-narrowed emission but also enhanced electroluminescence efficiency was observed, indicating that the threshold current density for lasing might be reduced.. |
| 573. | Katsuyuki Shizu, Jiyoung Lee, Hiroyuki Tanaka, Hiroko Nomura, Takuma Yasuda, Hironori Kaji, Chihaya Adachi, Highly efficient electroluminescence from purely organic donor-acceptor systems, PURE AND APPLIED CHEMISTRY, 10.1515/pac-2015-0301, 87, 7, 627-638, 2015.07, Thermally activated delayed fluorescence (TADF) emitters are third-generation electroluminescent materials that realize highly efficient organic light-emitting diodes (OLEDs) without using rare metals. Here, after briefly reviewing the principles of TADF and its use in OLEDs, we report a sky-blue TADF emitter, 9-(4-(benzo[d] thiazol-2-yl) phenyl)-N-3, N-3, N-6, N-6-tetraphenyl-9H-carbazole-3,6-diamine (DAC-BTZ). DAC-BTZ is a purely organic donor-acceptor-type molecule with a small energy difference between its lowest excited singlet state and lowest triplet state of 0.18-0.22 eV according to fluorescence and phosphorescence spectra of a DAC-BTZ-doped film. In addition, the doped film exhibits a high photoluminescence quantum yield of 0.82. Time-resolved photoluminescence measurements of the doped film confirm that DAC-BTZ emits TADF. An OLED containing DAC-BTZ as an emitter exhibits a maximum external quantum efficiency (EQE) of 10.3 %, which exceeds those obtained with conventional fluorescent emitters (5-7.5 %). TADF from DAC-BTZ makes a large contribution to the high EQE of its OLED.. |
| 574. | J. C. Ribierre; L. Zhao; S. Furukawa; T. Kikitsu; D. Inoue; A. Muranaka; K. Takaishi; T. Muto; S. Matsumoto; D. Hashizume; M. Uchiyama; P. André; C. Adachi; T. Aoyama, Ambipolar organic field-effect transistors based on solution-processed single crystal microwires of a quinoidal oligothiophene derivative, Chem. Comm., 10.1039/C4CC09608H, 51, 27, 5836-5839, 2015.02. |
| 575. | Masaki Numata; Takuma Yasuda; Chihaya Adachi, High efficiency pure blue thermally activated delayed fluorescence molecules having 10H-phenoxaborin and acridan units, Chem. Comm., 10.1039/C5CC00307E, 51, 46, 9443-9446, 2015.04. |
| 576. | Yan-qiong Zheng, William J. Potscavage, Jing Zhang, Takuma Yasuda, Bin Wei, Chihaya Adachi, Tetraphenyldibenzoperiflanthene as sensitizer for enhancing the performance in dinaphthothienothiophene-based photovoltaics with and without fullerene, SYNTHETIC METALS, 10.1016/j.synthmet.2015.04.002, 205, 121-126, 2015.07, In this work, various interlayers were inserted between the donor and acceptor in a dinaphthothienothiophene (DN'FF)/C-60 planar heterojunction (PHJ) to sensitize the performance. The power conversion efficiency is enhanced from 1.16% for the DNTT/C-60 PHJ cell to 2.23% by inserting a 5-nm-thick tetraphenyldibenzoperifianthene (DBP) interlayer because of the greatly improved photocurrent and open-circuit voltage (Voc). To achieve high Voc, fullerene-free PHJs of DNTT/boron subphthalocyanine chloride (SubPc) (donor/acceptor) were fabricated, and Voc is further improved by doping various fractions of DBP into the SubPc layer. The Voc clearly increases from 0.82V to 1.24V by 70 wt%-DBP doping and is accompanied by a slight increase in photocurrent. The bipolar transfer characteristics of SubPc and DBP are investigated by field-effect transistors and show that both can transport electrons, indicating their potential as acceptors in photovoltaic devices. When another 5-nm-thick SubPc layer was included in the fullerene-free DNTF/SubPc:DBP PHJ cell, the power conversion efficiency further increases to 1.32%. These results indicate that DBP is a promising sensitizer for enhancing the performance of DNIT-based photovoltaics. (C) 2015 Elsevier B.V. All rights reserved.. |
| 577. | Jeffrey G. Tait, Ewelina Witkowska, Masaya Hirade, Tung-Huei Ke, Pawel E. Malinowski, Soeren Steudel, Chihaya Adachi, Paul Heremans, Uniform Aerosol Jet printed polymer lines with 30 mu m width for 140 ppi resolution RGB organic light emitting diodes, ORGANIC ELECTRONICS, 10.1016/j.orgel.2015.03.034, 22, 40-43, 2015.07, We demonstrate the patterning of top emitting organic light emitting diodes (OLEDs) by direct-write Aerosol Jet printing in air from non-halogenated solvents. Indane was determined to be a suitable single solvent to dissolve the archetypal host poly(N-vinylcarbazole) and guest emitting dopants complexes for red, green, and blue OLEDs, and to print on both PEDOT:PSS and MoO3 transport layers. The Aerosol Jet deposition parameters were studied, including: atomization flow rate, exhaust flow rate, focusing sheath flow rate, nozzle-to-substrate distance, nozzle speed, and substrate temperature. A line width of 30 mu m and thickness of 30 nm was achieved, resulting in RGB OLEDs fabricated side-by-side with a pixel density of 140 ppi. (C) 2015 Elsevier B.V. All rights reserved.. |
| 578. | Miho Tsuwaki, Takashi Kasahara, Tomohiko Edura, Juro Oshima, Eri Kunisawa, Ryoichi Ishimatsu, Shigeyuki Matsunami, Toshihiko Imato, Chihaya Adachi, Shuichi Shoji, Jun Mizuno, Fabrication of a Portable Electrochemiluminescence-induced Fluorescence Detection Chip with Microfluidic Excitation Source for Point-of-care Diagnostics, IEEJ Transactions on Sensors and Micromachines, 10.1541/ieejsmas.135.230, 135, 6, 230-235, 2015.06. |
| 579. | Shuzo Hirata, Hyo Jung Heo, Yuki Shibano, Oamu Hirata, Masayuki Yahiro, and Chihaya Adachi, Improved Device Lifetime of Organic Light Emitting Diodes with an Electrochemically Stable-Conjugated Liquid Host in the Liquid Emitting Layer, Jpn. J. Appl.Phys., in press. |
| 580. | Hajime Nakanotani, CHIHAYA ADACHI, Amplified spontaneous emission and electroluminescence from thiophene/phenylene co-oligomer-doped p-bis(p-styrylstyryl)benzene crystals, Adv. Opt. Mater.. |
| 581. | Shuzo Hirata, Kentaro Totani, Hironori Kaji, Martin Vacha, Toshiyuki Watanabe, CHIHAYA ADACHI, Reversible thermal recording media using time-dependent persistent room temperature phosphorescence, Adv. Opt. Mater.. |
| 582. | Keigo Sato, Katsuyuki Shizu, Kazuaki Yoshimura, Atsushi Wada, Hiroshi Miyazaki, CHIHAYA ADACHI, Organic luminescent molecule with energetically equivalent singlet and triplet excited states for organic light-emitting diodes, Phys. Rev. Lett. |
| 583. | N. Suganuma, C.Adachi, T. Koyama, Y. Taniguchi and H. Shiraishi, A 200nm x 2mm array of organic light-emitting diodes and their anisotropic electroluminescence, Appl. Phys. Lett., 74, 1206-1208, 1999.03. |
| 584. | G. Sakamoto, C. Adachi, T. Koyama, Y. Taniguchi, C. D. Merritt, H. Murata and Z. H. Kafafi, Significant improvement of device durability in organic light-emitting diodes by doping both hole transport and emitter layers with rubrene molecules, Appl. Phys. Lett., 75, 766-768, 1999.08. |
| 585. | M. Uchida, C. Adachi, T. Koyama and Y. Taniguchi, Charge carrier trapping effect by luminescent dopant molecules in single-layer organic light emitting diodes, J. Appl. Phys., 86, 1680-1687, 1999.08. |
| 586. | A. Yamamori, C. Adachi, T. Koyama and Y. Taniguchi, Electroluminescence of organic light emitting diodes with a thick hole transport layer composed of a triphenylamine based polymer doped with an antimonium compound, J. Appl. Phys., 86, 4369-4376, 1999.10. |
| 587. | Y. Okumura, M. Nagawa, C. Adachi, M. Satsuki, S. Suga, T. Koyama and Y. Taniguchi, Low Threshold Gain-Narrowing Characteristics of Fluorescent Styrylbenzene Derivatives as a Guest Molecule in an Organic Thin-Film Optical Waveguide, Chem. Lett., 754-755, 2000.03. |
| 588. | G. Parthasarathy, C. Adachi, P. E. Burrows and S. R. Forrest, High-efficiency transparent organic light-emitting devices, Appl. Phys. Lett., 76, 2128, 2000.04. |
| 589. | C. Adachi, M. A. Baldo and S. R. Forrest, Electroluminescence mechanisms in organic light emitting devices employing a europium chelate doped in a wide energy gap bipolar conducting host, J. Appl. Phys., 87、8049-8055, 2000.06. |
| 590. | C. Adachi, M. A. Baldo, S. R. Forrest and M. E. Thompson, High-efficiency organic electrophosphorescent devices with tris(2-phenylpyridine)iridium doped into electron-transporting materials, Appl. Phys. Lett, 77, 904-906, 2000.08. |
| 591. | H. Mochizuki, T. Hasui, M, T. Shiono, T. Ikeda, C. Adachi, Y. Taniguchi, and Y. Shirota, Emission behavior of molecularly doped electroluminescent device using liquid-crystalline matrix, Appl. Phys. Lett., 77, 1587, 2000.09. |
| 592. | H. Mochizuki, T. Hasui, M. Kawamoto, M, T. Shiono, T. Ikeda, C. Adachi, Y. Taniguchi, and Y. Shirota, Novel liquid-crystalline and amorphous materials containing oxadiazole and amine moieties for electroluminescent devices, Chem. Commun., (19) 1923, 2000.09. |
| 593. | M. A. Baldo, C. Adachi and S. R. Forrest, Transient analysis of organic electrophosphorescence. Ⅱ. Transient analysis of triplet-triplet annihilation, Phys. Rev. B, 62, 10967, 2000.10. |
| 594. | H. Mochizuki, T. Hasui, O. Tsutsumi, A. Kanazawa, T. Shiono, T. Ikeda, C. Adachi, Y, Taniguchi and Y. Shirota, Electroluminescent Behavior of Oxadiazole Derivatives in Liquid-Crystalline Media, Mol. Cryst. and Liq. Cryst., 365, 129-138, 2001.01. |
| 595. | R. Naito, M. Ichikawa, T. Suzuki, C. Adachi, T. Koyama and Y. Taniguchi, Energy Relay Systems for Efficient Organic Light-Emitting Devices: Influence of Formation of Exciplex as Revealed by Photoexcitation, Mol. Cryst. and Liq. Cryst., 370, 31-34, 2001.01. |
| 596. | C. Adachi, R. Kwong and S. R. Forrest, Efficient electrophosphorescence using a doped ambipolar conductive molecular organic thin film, Organic Electronics, 2, 37-43, 2001.02. |
| 597. | S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq, Hae-Eun Lee, C. Adachi, P. E. Burrows, S. R. Forrest and M. E. Thompson, Highly Phosphorescent Bis-Cyclometalated Iridium Complexes: Synthesis, Photophysical Characterization, and Use in Organic Light Emitting Diodes, J. Am. Chem. Soc., 123, 4304-4312, 2001.04. |
| 598. | B. W. D’Andrade, M. A. Baldo, C. Adachi, J. Brooks, M. E. Thompson and S. R. Forrest, High-efficiency yellow double-doped organic light-emitting devices based on phosphor-sensitized fluorescence, Appl. Phys. Lett., 79, 1045-1047, 2001.08. |
| 599. | C. Adachi, Raymond C. Kwong, P. Djurovich, V. Adamovich, M. A. Baldo, M. E. Thompson and S. R. Forrest, Endothermic energy transfer: A mechanism for generating very efficient high-energy phosphorescent emission in organic materials, Appl. Phys. Lett., 79, 2082, 2001.09. |
| 600. | C. Adachi, M. A. Baldo, M. E. Thompson and S. R. Forrest, Nearly 100% internal phosphorescence efficiency in an organic light emitting device, J. Appl. Phys., 90, 5048-5051, 2001.11. |
| 601. | C. Adachi, M. E. Thompson and S. R. Forrest, Architectures for Efficient Electrophosphorescent Organic Light-Emitting Devices, IEEE, J Selected Topics Quan. Elec., 8, 372, 2002.03. |
| 602. | D. Kolosov, V. Adamovich, P. Djurovich, M. E. Thompson and C. Adachi, 1,8-Naphthalimides in Phosphorescent Organic LEDs : The Interplay between Dopant, Exciplex, and Host Emission, J. Am. Chem. Soc., 124, 9945-9954, 2002.07. |
| 603. | V. Adamovich, J. Brooks, A. Tamayo, A. M. Alexander, P. I. Djurovich, B. W. D’Andrade, C. Adachi, S. R. Forrest and M. E. Thompson, High efficiency single dopant white electrophosphorescent light emitting diodes, New J. Chem., 26, 1171-1178, 2002.08. |
| 604. | H. Yamamoto, T. Oyamada, H. Sasabe, and C. Adachi, Amplified spontaneous emission under optical pumping from an organic semiconductor laser structure equipped with transparent carrier injection electrodes, Appl. Phys. Lett., 84, 1401-1403, 2003.02. |
| 605. | H. Mochizuki, T. Hasui, M. Kawamoto, T. Ikeda, C. Adachi, Y. Taniguchi and Y. Shirota, A Novel Class of Photo- and Electroactive Polymers Containing Oxadiazole and Amine Moieties in a Side Chain, Macromolecules, 36, 3457-3464, 2003.04. |
| 606. | T. Oyamada, C. Maeda, H. Sasabe and C. Adachi, Efficient Electron Injection Characteristics of Tetra-2-pyridinylpyrazine (TPP) in Organic Light Emitting Diodes, Chem. Lett., 32, 388-389, 2003.04. |
| 607. | T. Oyamada, H. Tanaka, K. Matsushige, H. Sasabe and C. Adachi, Switching effect in Cu:TCNQ charge transfer-complex thin films by vacuum codeposition, Appl. Phys. Lett., 83, 1252-1254, 2003.08. |
| 608. | W. Yokoyama, H. Sasabe and C. Adachi, Carrier Injection and Transport of Steady-State High Current Density Exceeding 1000A/cm2 in Organic Thin Films, Jpn. J. Appl. Phys., (Express Letter), 42, L1353-1355, 2003.11. |
| 609. | T. Oyamada, C. Maeda, H. Sasabe and C. Adachi, Efficient Electron Injection Mechanism in Organic Light-Emitting Diodes Using an Ultra Thin Layer of Low-Work-Function Metals, Jpn. J. Appl. Phys., 42, L1535-1538, 2003.12. |
| 610. | X. F. Ren, B. D. Alleyne, P. I. Djurovich, C. Adachi, I. Tsyba, R. Bau and M. E. Thompson, Organometallic Complexes as Hole-Transporting Materials in Organic Light-Emitting Diodes, Inorg. Chem., 43, 1697-1707, 2004.02. |
| 611. | H. Inomata, K. Goushi, T. Masuko, T. Konno, T. Imai, H. Sasabe, J. J. Brown and C. Adachi, High-Efficiency Organic Electrophosphorescent Diodes Using 1, 3, 5-Triazine Electron Transport Materials, Chem. Mat., 16, 1285-1291, 2004.03. |
| 612. | Y. Kawamura, H. Yamamoto, K. Goushi, H. Sasabe and C. Adachi, Ultraviolet amplified spontaneous emission from thin films of 4,4’-bis(9-carbazolyl)-2,2’-biphenyl and the derivatives, Appl. Phys. Lett., 84, 2724-2726, 2004.04. |
| 613. | M. Ohkita, C. Adachi, M. Kawano, and T. Suzuki, Synthesis and characterization of hexakis(4-pyridylethynyl)benzene and hexakis(5-pyrimidylethynyl) benzene, Heterocycles, 63, 1537-1540, 2004.05. |
| 614. | T. Oyamada, H. Yoshizaki, H. Sasabe, and C. Adachi, Efficient Electron Injection Characteristics of Triazine Derivatives for Transparent OLEDs (TOLEDs), Chem. Lett., 33, 1034, 2004.05. |
| 615. | O. Karthaus, C. Adachi, S. Kurimura, and T. Oyamada, Electroluminescence from self-organized “microdomes”, Appl. Phys. Lett., 84, 4696, 2004.05. |
| 616. | 佐藤喜郎，合志憲一，雀部博之，Julie J. Brown，斉藤正美，安達千波矢, ２つのリン光性ドーパントを含有する白色リン光デバイスの発光機構, 電気学会論文誌Ａ, Vol.124, 414-420, 2004.05. |
| 617. | K. Goushi, Y. Kawamura, H. Sasabe, and C. Adachi, Unusual Phosphorescence Characteristics of Ir(ppy)3 in a Solid Matrix at Low Temperatures, Jpn. J. Appl. Phys., (Express Letter), 43, L937-939, 2004.06. |
| 618. | 小山田崇人，雀部博之，安達千波矢, フォトリソグラフィー法によるMgAu合金電極の形成と有機LED・有機FETへの適用, 電気学会論文誌C, 124, 1219-1223, 2004.06. |
| 619. | K. Goushi, R. Kwong, J. J. Brown, H. Sasabe and C. Adachi, Triplet exciton confinement and unconfinement by adjacent hole-transport layers, J. Appl. Phys., 95, 7798, 2004.06. |
| 620. | T. Oyamada, Y. Kawamura, T. Koyama, H. Sasabe and C. Adachi, Formation of Europium Chelate Complexes by Vacuum Co-Deposition and Their Application in Organic Light-Emitting Diodes, Adv. Mat., 16, 1082, 2004.07. |
| 621. | K. Hirata, T. Oyamada, T. Imai, H. Sasabe, C. Adachi, and T. Koyama, Electroluminescence as a probe for elucidating electrical conductivity in a deoxyribonucleic acid-cetyltrimethylammonium lipid complex layer, Appl. Phys. Lett., 85, 1627-1629, 2004.08. |
| 622. | Y. Kawamura, H. Sasabe, and C. Adachi, Simple Accurate System for Measuring Absolute Photoluminescence Quantum Efficiency in Organic Solid-State Thin Films, Jpn. J. Appl. Phys., 43, 7729-7730, 2004.11. |
| 623. | 安藤暢宏，河村祐一郎，Julie. J. Brown，雀部博之，安達千波矢, 複数のリン光発光層を含有する白色発光デバイス, 電気学会論文誌Ａ, 124, 1053-1058, 2004.11. |
| 624. | T. Oyamada, H. Sasabe, C. Adachi, S. Murase, T. Tominaga, and C. Maeda, Extremely low-voltage driving of organic light-emitting diodes with a Cs-doped phenyldipyrenylphosphine oxide layer as an electron-injection layer, Appl. Phys. Lett., 86, 033503, 2005.01. |
| 625. | M. Yoshida, T. Tsuchida, T. Kurata, M. Ikeda, H. Sasabe, and C. Adachi, High-Efficiency Carrier Injection Characteristics of Dixanthene Derivatives in Organic Light- Emitting Diodes, Jpn. J. Appl. Phys., 44, 410-411, 2005.01. |
| 626. | Takahito Oyamada, Hiroyuki Uchiuzo, Hiroyuki Sasabe and Chihaya Adachi, Blue-to-red electroluminescence from organic light-emitting field-effect transistor using various organic semiconductor materials, J. SID, 13, 869, 2005.02. |
| 627. | T. Oyamada, H. Sasabe, C. Adachi, S. Okuyama, N. Shimoji, and K. Matsushige, Electroluminescence of 2,4-bis(4-(2’-thiophene-yl)phenyl)thiophene in organic light-emitting field-effect transistors, Appl. Phys. Lett., 86, 093505-1-093505-3, 2005.02. |
| 628. | T. Aimono, Y. Kawamura, K. Goushi, H. Yamamoto, H. Sasabe, and C. Adachi, 100% fluorescence efficiency of 4,4’-bis[(N-carbazole)styryl]biphenyl in a solid film and the very low amplified spontaneous emission threshold, Appl. Phys. Lett., 86, 071110, 2005.02. |
| 629. | H. Yamamoto, H. Kasajima, W. Yokoyama, H. Sasabe, and C. Adachi, Extremely-high-density carrier injection and transport over 12000A/cm2 into organic thin films, Appl. Phys. Lett., 86, 083502-1-083502-3, 2005.02. |
| 630. | Y. Kawamura, K. Goushi, J. Brooks, J. J. Brown, H. Sasabe and C. Adachi, 100% phosphorescence quantum efficiency of Ir(III) complexes in organic semiconductor films, Appl. Phys. Lett., 86, 071104, 2005.02. |
| 631. | K. Goushi, H. Sasabe, and C. Adachi, Phosphorescence Decay Mechanism of Ir(ppy)3 in a Solid Matrix, J. Photopolymer Sci. & Tech., 18, 47-50, 2005.05. |
| 632. | H. Nakanotani, H. Sasabe, and C. Adachi, Singlet-singlet and singlet-heat annihilations in fluorescence-based organic light-emitting diodes under steady-state high current density, Appl. Phys. Lett., 86, 213506-1-213506-3, 2005.05. |
| 633. | H. Nakanotani, T. Oyamada, Y. Kawamura, H. Sasabe, and C. Adachi, Injection and Transport of High Current Density over 1000 A/cm2 in Organic Light Emitting Diodes under Pulse Excitation, Jpn. J. Appl. Phys., 44, 3659-3662, 2005.06. |
| 634. | Takahito Oyamada, Hiroyuki Uchiuzo, Seiji Akiyama, Yoshiaki Oku, Noriyuki Shimoji, Kazumi Matsushige, Hiroyuki Sasabe, and Chihaya Adachi, Lateral organic light-emitting diode with field-effect transistor characteristics, J. Appl. Phys., 98, 074506, 2005.10. |
| 635. | Toshinori Matsushima, Hiroyuki Sasabe, and Chihaya Adachi, Carrier injection and transport characteristics of copper phthalocyanine thin films under low to extremely high current densities, Appl. Phys. Lett., 88, 033508, 2006.01. |
| 636. | Yuichiro Kawamura, Jason Brooks, Julie J. Brown, H. Sasabe, and C. Adachi, Intermolecular Interaction and a Concentration-Quenching Mechanism of Phosphorescent Ir(III) Complexes in a Solid Film, Phys. Rev. Lett., 96, 017404, 2006.01. |
| 637. | O. Karthaus, C. Adachi, S. Arakaki, A. Endo and T. Wada, Preparation of Micropatterned Organic Light Emitting Diodes by Self-Organization, Molecular Crystals and Liquid Crystals, 444, 87-94, 2006.01. |
| 638. | 安達千波矢, 発光型有機ＦＥＴ, Molecular Electronics & Bioelectronics, Vol.17, 35-38, 2006.02. |
| 639. | Takahito Oyamada, Seiji Akiyama, Masayuki Yahiro, Mari Saigou, Motoo Shiro, Hiroyuki Sasabe, and Chihaya Adachi, Unusual photoluminescence characteristics of tetraphenylpyrene (TPPy) in various aggregated morphologies, Chem. Phys. Lett., 421, 295-299, 2006.02. |
| 640. | Hidetoshi Yamamoto, Takahito Oyamada, William Hale, Shoichi Aoshima, Hiroyuki Sasabe, and Chihaya Adachi, Low-Damage Indium Tin Oxide Formation on Organic Layers Using Unique Cylindrical Sputtering Module and Application in Transparent Organic Light-Emitting Diodes, Jpn. J. Appl. Phys., 45, L213-216, 2006.02. |
| 641. | Takahito Oyamada, Hiroyuki Sasabe, Yoshiaki Oku , Noriyuki Shimoji, and Chihaya Adachi, Estimation of carrier recombination and electroluminescence emission regions in organic light-emitting field-effect transistors using local doping method, Appl. Phys. Lett., 88, 093514, 2006.03. |
| 642. | Kenichi Goushi, Jason Brooks, Julie. J. Brown, Hiroyuki Sasabe, and Chihaya Adachi, Spin-relaxation Process of Excited Triplet States of Ir(ppy)3, J. Photopolymer Sci. & Tech., 19, 181-186, 2006.05. |
| 643. | John A. Mikroyannidis, Helen A. Moshopoulou, John A. Anastasopoulos, Minas M. Stylianakis, Larysa Fenenko, and Chihaya Adachi, Novel Blue-Greenish Electroluminescent Poly(Fluorenevinylene-alt-Dibenzothiophenevinylene)s and their Model Compounds, J. Poly. Sci., A: Poly. Chem., 44, 6790-6800, 2006.07. |
| 644. | 小山田崇人，安達千波矢, 低電圧駆動を目指した低分子有機ＥＬ素子, 日本画像学会誌, Vol. 45 (2006), No.1, 59-65, 2006.08. |
| 645. | J. A. Mikroyannidis, L. Fenenko, and C. Adachi, Synthesis and Photophysical Characteristics of 2,7-Fluorenevinylene-based Trimers and their Electroluminescence, J. Phys. Chem. B, 110, 20317-26, 2006.09. |
| 646. | 遠藤礼隆，J. Brooks，J. J. Brown，雀部博之，安達千波矢, シロキサン化合物を発光層のホスト材料として用いた青色有機ELデバイスの素子特性, 高分子論文集, 63, 686-689, 2006.10. |
| 647. | 古酒慎也，丸山純夫，雀部博之，安達千波矢, 可溶性トリス（8-キノリノレート）アルミニウム含有デンドリマーの発光特性, 高分子論文集, 63, 675-680, 2006.10. |
| 648. | K. S. Son, T. Mishina, S. Yamamoto, J. Nakahara, C. Adachi, and Y.Kawamura, Topological change of 4, 4’-bis[9-dicarbazolyl]-2,2’-biphenyl (CBP) by intermolecular rearrangement, Proceeding of the international symposium on TOP, World Scientific Publishing, 124-128 (2006), 2006.11. |
| 649. | 安達千波矢，松島敏則，中野谷一, 有機発光ダイオードから有機レーザーへの応用展開, 光学, 第35巻, 11号, 556-563, 2006.11. |
| 650. | Takahito Oyamada, Chihaya Adachi, Chung-Chih Wu, Chih-Hao Chang, Ken-Tsung Wong, Teng-Chih Chao, and Fu-Chuan Fang, Optical properties of oligo(9,9-diaryfluorene) derivatives in thin films and their application for organic light-emitting field-effect transistors, J. Phys. Chem. C, 111 , 108-115 (2007), 2006.12. |
| 651. | 安達千波矢，河村祐一郎，合志憲一，遠藤礼隆, 強リン光性分子薄膜の開発と発光デバイスへの応用, 応用物理, Vol.75, No.12, 1465-1470, 2006.12. |
| 652. | 松島敏則, 安達千波矢, 有機薄膜への高電流密度の注入と低電流密度から高電流密度域におけるキャリア輸送特性, Molecular Electronics and Bioelectronics, Vol.17, No.4 (2006.12), 245-250 (1-6), 2006.12. |
| 653. | T. Matsushima and C. Adachi, Extremely low-voltage organic light-emitting diodes with p-doped alpha-sexithiophene hole transport and n-doped phenyldipyrenylphosphine oxide electron transport layers, Appl. Phys. Lett., 89, 253506, 2006.12. |
| 654. | Takahito Oyamada, Guang Shao, Hiroyuki Uchiuzou, Hajime Nakanotani, Akihiro Orita, Junzo Otera, Masayuki Yahiro, and Chihaya Adachi, Optical and electrical properties of quinqueacetylphenyl derivatives and the application for organic field-effect transistors, Jpn. J. Appl. Phys., 45, L1331-1333, 2006.12. |
| 655. | Atsushi Takahashi, Ayataka Endo and Chihaya Adachi, Novel Electron-transporting Carbazolylphenylquinolines for the Phosphorescent Organic Light Emitting Diodes, Jpn. J. Appl. Phys., 45, 9228-9230, 2006.12. |
| 656. | L. Fenenko and C. Adachi, Influence of heat treatment on indium-tin-oxide anodes and copper phthalocyanine hole injection layers in organic light-emitting diodes, Thin Solid Films, 515, 4812-4818, 2007.01. |
| 657. | Toshinori Matsushima, Kenichi Goushi, and Chihaya Adachi, Charge-carrier injection characteristics at organic/organic heterojunction interfaces in organic light-emitting diodes, Chem. Phys. Lett., 435, 327-330, 2007.01. |
| 658. | 安達千波矢, 小山田崇人, 松島敏則, キャリア注入・輸送層ドーピングによる有機LEDの特性向上, Molecular Electronics and Bioelectronics, Vol.18, No.1, (2007.2), 25-30, 2007.02. |
| 659. | Hiroshi Kanno, Kaori Ishikawa, Yoshitakta Nishio, Ayataka Endo, Chihaya Adachi, Kenichi Shibata, Highly efficient and stable red phosphorescent organic light-emitting device using bis[2-(2-benzothiazoyl)phenolato]zinc(II) as host material, Appl. Phys. Lett., 90, 123509, 2007.03. |
| 660. | Yuhki Terao, Hiroyuki Sasabe and Chihaya Adachi, Correlation of hole mobility, exciton diffusion length, and solar cell characteristics in phthalocyanine/fullerene organic solar cells, Appl. Phys. Lett., 90, 103515, 2007.03. |
| 661. | John A. Mikroyannidis, Larysa Fenenko, Masayuki Yahiro, and Chihaya Adachi, Altarnating Copolyfluorenevinyles with Polynuclear Aromatic Moieties: Synthesis, Photophysics, and Electroluminescence, J. Poly. Sci.,A: Poly. Chem., 45, 4661-4670 (2007), 2007.04. |
| 662. | Hajime Nakanotani, Seiji Akiyama, Dai Ohnishi, Masato Moriwake, Masayuki Yahiro, Toshitada Yoshihara, Seiji Tobita and Chihaya Adachi, Extremely Low-Threshold Amplified Spontaneous Emission of 9,9'-Spirobifluorene Derivatives and Electroluminescence from Field-Effect Transistor Structure, Advanced Functional Materials, 17,2328-2335 (2007), 2007.04. |
| 663. | Makoto Nakahara, Masahiro Minagawa, Takahito Oyamada, Toyoyasu Tadokoro, Hiroyuki Sasabe and Chihaya Adachi, Analysis of Carrier Traps in Continuously Operated 4,4'-bis [N-(1-naphthyl)-N-phenyl-amino]-biphenyl/tris(8-gydroxyquinoline) aluminum-Based Organic Light-Emitting Diodes by Thermally Stimulated Current Measurement, Jpn.J.Applied.Physics, Part Ⅱ、46、L636-639 (2007), 2007.04. |
| 664. | H. Nakanotani, C. Adachi, S. Watanabe, and R. Katoh, Spectrally Narrow Emission from Organic Films Under Continuous-Wave Excitation, Appl.Pys.Lett., 90,231109, 2007.04. |
| 665. | Satria Zulkarnaen Bisri, Tetsuo Takahashi, Taishi Takenobu, Masayuki Yahiro, Chihaya Adachi, and Yoshihiro Iwasa, Ambipolar Field-Effect Transistor of High Photoluminescent Material Tetraphenylpyrene(TTPy) Single Crystal, Jpn.J.Appl.Phys., L596-L598, 2007.04. |
| 666. | Takahito Oyamada, Chih-Hao Chang, Teng-Chih Chao, Fu-Chuan Fang, Chung-Chih Wu, Ken-Tsung Wong, Hiroyuki Sasabe, and Chihaya Adachi, Optical Properties of Oligo(9,9-diarylfluorene) Derivatives in Thin Films and Their Application for Organic LIght-Emitting Field-Effect Transistors, J. Phys. Chem., 108-115, 2007.04. |
| 667. | M. Aonuma, T. Oyamada, T. Miki, H. Sasabe and C. Adachi, Material design of hole transport materials capable of thick film formation in organic light emitting diodes, Appl. Phys. Lett., 90, 183503 (2007), 2007.04. |
| 668. | Tomo Sakanoue, Masayuki Yahiro, Chihaya Adachi, Hiroyuki Uchiuzou, Takahashi Takayoshi and Akio Toshimitsu, Ambipolar light-emitting organic field-effect transistors using a wide-band-gap blue-emitting small molecule, Appl. Phys. Lett., 90, 171118 (2007), 2007.04. |
| 669. | Takahito Oyamada, Yusuke Sugawara, Yuhki Terao, Hiroyuki Sasabe and Chihaya Adachi, Top Light-Harvesting Organic Solar Cell Using Ultrathin Ag / MgAg Layer as Anode, Jpn. J. Appl. Phys., 46, 1734-1735 (2007), 2007.04. |
| 670. | Toshinori Matsushima and Chihaya Adachi, Observation of Extremely High Current Densities on Order of MA/cm2 in Copper Phthalocyanine Thin-Film Devices with Submicron Active Areas, Jpn. J. Appl. Phys., 46, L1179-L1181 (2007), 2007.07. |
| 671. | Larysa Fenenko, Guoliang Mao, Akihiro Orita, Junzo Otera, Petro Smertenko, Georgi Svechnikov, Jun-ichi Nishide, Hiroyuki Sasabe, and Chihaya Adachi, 1,4-bis(2,2-diphenylethenyl) benzene as an efficient emitting material for organic light emitting diodes, Semiconductor Physics, Quantum Electronics & Optoelectronics, 10,77-82 (2007), 2007.07. |
| 672. | 安達千波矢、 小山田崇人、松島敏則, 化学ドーピングによる有機ＥＬ素子の低駆動電圧化 Lowering the Driving Voltage of Organic Lihgt Emitting Diodes by Chemical Doping, 表面科学, 28, 2636-241 (2007), 2007.07. |
| 673. | L. Fenenko, C. Adachi, Y. Nakanishi, P. Smertenko, and S. Svechinikov, Features of conductivity and electroluminescence of new poly (9,9-dioctylfluorenyl-2,7-diyl) - End capped with polyhedral oligomeric silsesquioxanes, Mol. Cryst. LIq. Cryst., 467, 303-309 (2007), 2007.07. |
| 674. | Daisuke Yokoyama, Hajime Nakanotani, Yousuke Setoguchi, Masato Moriwake, Dai Ohnishi, Masayuki Yahiro, and Chihaya Adachi, Spectally Narrow Emission at Cutoff Wavelength from Edge of Electrically Pumped Organic Light-Emitting Diodes, Jpn. J. Appl. Phys., 46, L826-L829 (2007), 2007.07. |
| 675. | Toshinori Matsushima, Masayuki Yahiro, and Chihaya Adachi, Estimation of electron traps in carbon-60 field-effect transistors by a thermally stimulated cureent technique, Appl. Phys. Lett., 91, 103505 (2007), 2007.07. |
| 676. | Toshinori Matsushima and Chihaya Adachi, High-current Injection and Transport on Order of kA/cm2 in Organic Light-emitting Diodes Having Mixed Organic/Organic Heterojunction Interfaces, Jpn. J. Appl.Phys., 46, L861-L863 (2007), 2007.07. |
| 677. | Hajime Nakanotani, Naoki Matsumoto, Hiroyuki Uchiuzou, Masakazu Nishiyama, Masayuki Yahiro and Chihaya Adachi, Very low amplified spontaneous emission threshold and electroluminescence characteristics of 1,1'-diphenyl substituted fluorene derivatives, Optical Materials, 30, 630-636 (2007), 2007.07. |
| 678. | Kyung Soo Son, Masayuki Yahiro, Toshiro Imai, Hiroki Yoshizaki and Chihaya Adachi, Blue Organic Electrophosphorescence Diodes using Diarylamino-substituted Heterocyclic Compounds as Host Material, J. Photopolymer Sci. & Tech., 20, 47-51(2007), 2007.07. |
| 679. | Hajime Nakanotani, Masayuki Yahiro, Koki Yano and Chihaya Adachi, Ambipolar field-effect transistor based on organic-inorganic hybrid structure, Appl. Phys. Lett., 90, 262104 (2007), 2007.07. |
| 680. | Kinoshita Shohei, Sakanoue Tomo, Yahiro Masayuki, Takimiya Kazuo, Ebata Hideaki, Ikeda Masaaki, Kuwabara Hirokazu, Adachi Chihaya, A high mobility ambipolar field effect transistor using a 2,6-diphenylbenzo[1,2-b : 4,5-b']diselenophene/fullerene double layer, SOLID STATE COMMUNICATIONS, 10.1016/j.ssc.2007.10.017, 145, 3, 114-117, 2008.01. |
| 681. | 八尋 正幸、坂上 知、内生蔵 広幸、小山田 崇人、年光 昭夫、安達 千波矢, 発光性有機トランジスタ用材料の分子設計とデバイス特性, 有機合成化学協会誌, 66,493(2008), 2008.02. |
| 682. | Toshinori Matsushima and Chihaya Adachi, Suppression of exciton annihilation at high current densities in organic light-emittingdiode resulting from energy-level alignments of carrier transport layers, Appl.Phys. Lett., 92,063306(2008), 2008.02. |
| 683. | Tatsushi Baba, Hisashi Shimakoshi, Ayataka Endo, Chihaya Adachi, Yoshio Hisaeda, Photophysical and photocatalytic properties of beta-sulfonatoporphycenes, CHEMISTRY LETTERS, 10.1246/cl.2008.264, 37, 3, 264-265, 37,264-265(2008), 2008.03, The photophysical properties and photooxidation ability of the beta-sulfonatoporphycenes are reported. The photophysical parameters depend on the number of substitutions. The disulfonated porphycene 2 is expected to be a new photosensitizer due to its high catalytic activity and photostability.. |
| 684. | Tomo Sakanoue, Masayuki Yahiro, Chihaya Adachi, Jeremy H. Burroughes, Yoshiaki Oku, Noriyuki Shimoji, Takayoshi Takahashi, Akio Toshimitsu, Alignment-free process for asymmetric contact electrodes and their application in light-emitting organic field-effect transistors, APPLIED PHYSICS LETTERS, 10.1063/1.2839895, 92, 5, 92,053505(2008), 2008.02, We developed an alignment-free process for asymmetric contacts of Au and Al and applied it to light-emitting organic field-effect transistors. Because electrons were injected efficiently from Al contacts, the emission intensity and onset voltages for light were significantly better than those in a device with conventional Au/Cr contacts. Moreover, a device with 1 mu m channel length asymmetric contacts of Au and Al showed about 50 times higher current than that of the device with conventional Au/Cr contacts. This significant improvement can be ascribed to both dual space-charge formation of holes and electrons and low carrier injection barriers. (c) 2008 American Institute of Physics.. |
| 685. | Toshinori Matsushima, Chihaya Adachi, Enhanced hole injection and transport in molybdenum-dioxide-doped organic hole-transporting layers, JOURNAL OF APPLIED PHYSICS, 10.1063/1.2836972, 103, 3, 103,034501(2008), 2008.02, We have found that molybdenum dioxide (MoO(2)) is an excellent dopant for enhancing electrical conductivities in organic hole-transporting layers. We fabricated hole-only devices with an alpha-sexithiophene (alpha-6T) layer doped with MoO(2) at various concentrations to investigate how doping MoO(2) into the alpha-6T layers influences the hole-injection and hole-transport characteristics of these layers. We observed a marked increase in electrical conductivity as a result of the MoO(2) doping. The 30-mol % MoO(2)-doped alpha-6T layer had a high electrical conductivity of 8.9 +/- 1.3x10(-6) S/cm. From the results of our visible/near-infrared absorption spectra study of these doped layers, we confirmed that this increase in electrical conductivity is caused by a charge transfer between MoO(2) and alpha-6T, which leads to an increase in free hole concentration in the doped layers and the formation of an ohmic contact at an electrode/alpha-6T interface. In the latter part of this paper, we discuss current flow and electroluminescence (EL) characteristics of organic light-emitting diodes (OLEDs) with a 30-mol % MoO(2)-doped alpha-6T hole-transporting layer and a 30-mol % Cs-doped phenyldipyrenylphosphine oxide (POPy(2)) electron-transporting layer. We achieved an extremely low driving voltage of 3.1 V required for a current density of 100 mA/cm(2) in the doped OLEDs owing to the use of the alpha-6T and POPy(2) layers with high carrier mobilities and the excellent p-type MoO(2) and n-type Cs dopants. We demonstrated the enhancement of power efficiencies by approximate to 2 times in the doped OLEDs compared with undoped OLEDs and observed bright EL at low driving voltages in the doped OLEDs, for example, 100 cd/m(2) at 2.3 V, 1000 cd/m(2) at 2.7 V, and 10 000 cd/m(2) at 3.3 V. (c) 2008 American Institute of Physics.. |
| 686. | Taishi Takenobu, Satria Zulkarnaen Bisri, Tetsuo Takahashi, Masayuki Yahiro, Chihaya Adachi, Yoshihiro Iwasa, High current density in light-emitting transistors of organic single crystals, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.100.066601, 100, 6, 066601, 100, 066601(2008), 2008.02, We measured the external electroluminescence quantum efficiency (eta(ext)) in light-emitting field-effect transistors (LETs) made of organic single crystals and found that, in the ambipolar transport region, eta(ext) is not degraded up to several hundreds A/cm(2) current-density range, which is 2 orders of magnitude larger than that achieved in conventional organic light-emitting diodes. The present result indicates the single-crystal organic LET is a promising device structure that is free from various kinds of nonradiative losses such as exciton dissociation near electrodes and exciton annihilations.. |
| 687. | Toshinori Matsushima, Chihaya Adachi, Evaluating origin of electron traps in tris(8-hydroxyquinoline) aluminum thin films using thermally stimulated current technique, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.1143/JJAP.47.1748, 47, 3, 1748-1752, 47,1748(2008), 2008.03, We measured the energy distributions and concentrations of electron traps in O(2)-unexposed and O(2)-exposed tris(8-hydroxyquinoline) aluminum (Alq(3)) films using a thermally stimulated current (TSC) technique to investigate how doping O(2) molecules in Alq(3) films affect the films' electron trap and electron transport characteristics. The results of our TSC studies revealed that Alq(3) films have an electron trap distribution with peak depths ranging from 0.075 to 0.1 eV and peak widths ranging from 0.06 and 0.07 eV. Exposing the Alq3 films to O(2) atmosphere induced a marked increase in electron trap concentration, indicating that electron traps with an energy distribution originate from O(2) molecules absorbed in Alq(3) films. We measured the current density-voltage characteristics of these films. The driving and turn-on voltages of the O(2)-exposed Alq(3) film became higher than those of the O(2)-unexposed Alq(3) film owing to the increase in electron trap concentration caused by the O(2) doping of the Alq(3) films.. |
| 688. | Hisashi Shimakoshi, Tatsushi Baba, Yusuke Iseki, Isao Aritome, Ayataka Endo, Chihaya Adachi and Yoshio Hisaeda, Photophysical and Photosensitizing properties of brominated porphycenes, Chem.Comm., 2882(2008), 2008.04. |
| 689. | Toshinori Matsushima, Chihaya Adachi, Highly efficient organic light-emitting diodes doped with thiophene/phenylene co-oligomer, CHEMISTRY OF MATERIALS, 10.1021/cm80009817, 20, 9, 2881-2883, 20, 2881-2883(2008), 2008.05. |
| 690. | Naoki Matsumoto, Masakazu Nishiyama, Chihaya Adachi, Exciplex formation between Alq3 and hole transport materials and their photo-and electroluminescence characteristics, J.Phys.Chem.C., 112, 7735-7741(2008), 2008.04. |
| 691. | Toshinori Matsushima, Chihaya Adachi, Bright electroluminescence from single-layer organic light-emitting diodes comprising an ambipolar carrier transport layer of phenyldipyrenylphosphine oxide, THIN SOLID FILMS, 10.1016/j.tsf.2007.09.038, 516, 12, 4288-4292, 516, 4288-4292 (2008), 2008.04, We investigated the carrier transport and recombination characteristics of single-layer organic light-emitting diodes (SLOLEDs) composed of a phenyldipyrenylphosphine oxide (POPy2) layer doped with orange fluorescent molecules of 2,5-bis-[bis-(4-methoxy-phenyl)-amino}-styryl]-terephthalonitrile (BST). The SLOLEDs achieved a high external quantum efficiency of 1.6% and a high luminance of 24,000 cd/m(2) at a low driving voltage of 8 V These very good electrolummescence characteristics originate from factors that include our use of the following: (1) the ambipolar POPy2 layer, which can transport balanced amounts of electrons and holes, (2) a high BST-doping concentration that traps injected carriers on BST molecules, and (3) insertion of an undoped POPy2 layer next to a metallic cathode to prevent exciton quenching. (c) 2007 Elsevier B.V. All rights reserved.. |
| 692. | Larysa Fenenko, Guang Shao, Akihiro Orita, Masayuki Yahiro, Funzo Otera, Sergei Svechnikov, and Chihaya Adachi, Electrical Properties of 1,4-bis(4-(phenylethynyl)Phenylethynyl)Benzene and its Application for Organic Light Emitting Diodes, Chem.Commin, 2278-2280, 2008.04. |
| 693. | Ayataka Endo, Kengo Suzuki, Toshitada Yoshihara, Seiji Tobita, Masayuki Yahiro, Chihaya Adachi, Measurement of photoluminescence efficiency of Ir(III) phenylpyridine derivatives in solution and solid-state films, CHEMICAL PHYSICS LETTERS, 10.1016/j.cplett.2008.05.064, 460, 1-3, 155-157, 460,155-157(2008), 2008.07, We compared the photoluminescence efficiency (Phi(PL)) of fac-tris(2-phenylpyridine) iridium (Ir(ppy)(3)) and derivatives of it in solution and in doped solid-state films and estimated their radiative and nonradiative decay rates. The green phosphor of Ir(ppy)(3) and blue phosphors of FIrpic, Ir(Fppy)(3), FIr6 showed high Phi(PL) values approaching to 100% in both solution and doped solid-state films. On the other hand, the red phosphor of Btp(2)Ir(acac) showed lower Phi(PL) value less than 40% in both environments. Photoacoustic spectroscopy results indicated that for Btp(2)Ir(acac) nonradiative decay from the triplet state to the ground states is 64 +/- 8%. (C) 2008 Elsevier B.V. All rights reserved.. |
| 694. | Tomo Sakanoue, Masayuki Yahiro, Chihaya Adachi, Kazuo Takimiya, Akio Toshimitsu, Electrical characteristics of single-component ambipolar organic field-effect transistors and effects of air exposure on them, JOURNAL OF APPLIED PHYSICS, 10.1063/1.2919738, 103, 9, 103, 094509(2008), 2008.05, We investigated the electrical characteristics of single-component ambipolar organic field-effect transistors (OFETs) by controlling the device structure and preparation and the measurement conditions. Six organic semiconductor materials (copper-phthalocyanine, tris-(8-hydroxyquinoline)aluminum (Alq(3)), alpha-sexithiophene, 4-4'-bis-styrylphenyl, 2,7-diphenyl[1]benzothieno[3,2-b]benzothiophene, or a photopolymerized polydiacethylene derivative (PDA) were used as the active layer, and all were found to transport both holes and electrons. The PDA-based FETs had the highest hole and electron mobilities (0.12 and 0.025 cm(2)/V s, respectively). We also investigated the effect of air exposure on the OFETs. The hole mobility was barely affected by the exposure while the electron mobility was significantly affected. The threshold voltage for p-channel operation was shifted by the exposure while that for n-channel operation was not, indicating that the hole density in the active layer is increased by air exposure whereas the electron density is independent of air exposure. Furthermore, we prepared an Alq(3)-based p-channel OFET and investigated the effect of air exposure on it. While its operation was stable in vacuum, air exposure degraded its characteristics. These behaviors indicate that irreversible chemical reactions occur between cationic Alq(3) species and oxygen or water molecules. (C) 2008 American Institute of Physics.. |
| 695. | Kyung Soo Son, Masayuki Yahiro, Toshiro Imai, Hiroki Yoshizaki, Chihaya Adachi, Analyzing bipolar carrier transport characteristics of diarylamino-substituted heterocyclic compounds in organic light-emitting diodes by probing electroluminescence spectra, CHEMISTRY OF MATERIALS, 10.1021/cm8004985, 20, 13, 4439-4446, 20,4439-4446(2008), 2008.07, We analyzed bipolar carrier transport characteristics of diarylamino-substituted heterocyclic compounds (DAHCs) having benzene, pyridine, pyrimidine, or triazine electron-accepting core units and carbazole or beta-naphthylamine as electron-donating substituents. The highest occupied molecular and lowest unoccupied molecular orbital levels, carrier injection, and transport characteristics were systematically controlled by changing combinations of the core and substituent units. By analyzing electroluminescence spectra as a probe in four kinds of organic light emitting diode (OLED) structures, we found that the carrier transport characteristics of DAHCs significantly change depending on device structure. We concluded that all DAHCs have bipolar carrier transport characteristics, that is, DAHCs intrinsically possess both hole and electron mobilities that are based on unique molecular structures having both electron -donating and -accepting units. We also demonstrated that carrier injection barriers between DAHCs and adjacent carrier transport layers virtually control the appearance of bipolar characteristics in OLEDs.. |
| 696. | Toshinori Matsushima and Chihaya Adachi, Temperature-independent current density voltage characteristics in tris(8-hydroxyquinoline)aluminum thin films, Thin Solid Films, 516, 5069(2008), 2008.06. |
| 697. | Hajime Nakanotani, Ryota Kabe, Masayuki Yahiro, Taishi Takenobu, Yoshihiro Iwasa, Chihaya Adachi, Blue-light-emitting ambipolar field-effect transistors using an organic single crystal of 1,4-Bis(4-methylstyryl)benzene, APPLIED PHYSICS EXPRESS, 10.1143/APEX.1.091801, 1, 9, 1, 091801, 2008.09, An ambipolar light-emitting organic field-effect transistor (LE-OFET) based on a 1,4-Bis(4-methylstyryl)benzene (BSB-Me) single crystal was developed. The BSB-Me single crystal has very high photoluminescence quantum efficiency (phi(PL)) of 89 +/- 2%, while phi(PL) of the BSB-Me vapor-deposited film is limited to a much lower value of 54 +/- 2%. Ambipolar operation with successive blue electroluminescence from the FETs based on the BSB-Me single crystals was demonstrated by realizing nearly equal electron and hole mobilities [about 0.005 cm(2)/(V s)] with asymmetric gold-calcium contacts. Since BSB-Me single crystals can perform light amplification, the BSIB-Me-based ambipolar LE-OFET is a promising candidate for future electrically driven organic blue-emitting solid-state lasers. (C) 2008 The Japan Society of Applied Physics.. |
| 698. | Kyung Soo Son, Masayuki Yariro, Toshiro Imai, Hiroki Yoshizaki, Junichi Nishide, Hiroyuki Sasabe, Chihaya Adachi, Roll-off characteristics of electroluminescence efficiency of organic blue electrophosphorescence diodes, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.1143/JJAP.47.7363, 47, 9, 7363-7365, 47, 7363(2008), 2008.09, We studied the relaxation of electroluminescence roll-off characteristics by changing the dopant concentration and thickness of the emitting layer in organic blue electrophosphorescence diodes composed of 2,6-dicarbozolo-1.5-pyridine host doped with iridium(III)-bis[(4,6-di-fluorophenyl)-pyridinato-NC(2)]picolinate. Analyzing the roll-off characteristics using the theoretical models of triplet-triplet annihilation and triplet-polaron annihilation (TPA). We found that the roll-off characteristics of these devices were determined primarily by TPA.. |
| 699. | Daisuke Yokoyama, Akio Sakaguchi, Michio Suzuki, Chihaya Adachi, Horizontal molecular orientation in vacuum-deposited organic amorphous films of hole and electron transport materials, APPLIED PHYSICS LETTERS, 10.1063/1.2996258, 93, 17, 93, 173302(2008), 2008.10, Using wide-range variable angle spectroscopic ellipsometry, the authors demonstrate large optical uniaxial anisotropy of vacuum-deposited organic amorphous films of hole and electron transport materials having long or planar molecular structures. The ordinary refractive indices and extinction coefficients were higher than the extraordinary ones, revealing that the molecules in the amorphous films are horizontally oriented. The horizontal orientation requires significant modifications in the understanding of both the electrical and optical characteristics of amorphous films when we use materials having long or planar molecular structures. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2996258]. |
| 700. | Hisashi Shimakoshi, Tatsushi Baba, Yusuke Iseki, Ayataka Endo, Chihaya Adachi, Midori Watanabe, Yoshio Hisaeda, Photosensitizing properties of the porphycene immobilized in sol-gel derived silica coating films, TETRAHEDRON LETTERS, 10.1016/j.tetlet.2008.08.003, 49, 43, 6198-6201, 49,6198-6201(2008), 2008.10, Porphycene was covalently immobilized in a sol-gel silica film deposited on a glass plate, and the immobilized porphycene showed a photosensitizing property with recycling for the photo-oxidation of 1,5-dihydroxynaphthalene. (C) 2008 Elsevier Ltd. All rights reserved.. |
| 701. | Hsiao-Wen Hung, Norimasa Yokoyama, Masayuki Yahiro, Chihaya Adachi, Low driving voltage organic light emitting diode using phenanthrene oligomers as electron transport layer, THIN SOLID FILMS, 10.1016/j.tsf.2008.05.047, 516, 23, 8717-8720, 516, 8717(2008), 2008.10, We demonstrate that an electron transport material, 2-(phenanthren-10-yl)-7-(phenanthren-9-yl)phenanthrene (Phen-A), significantly lowers the driving voltage in organic light emitting diodes. In a device structure of indium tin oxides (110 nm)/N,N'-di(alpha-naphtyl)-N,N'-diphenyl-benzidine (50 nm)/tris-(8-hydroxy quinoline)aluminum (20 nm)/Phen-A (30 nm)/MgAg(100 nm)/Ag (10 nm), a very low driving voltage of 5.8 V was obtained at a current density of 100 mA/cm(2). We clarified that Phen-A has a preferred the lowest unoccupied molecular orbital level and a characteristic polycrystalline texture, which are ascribed to the reason for the improved electron injection efficiency at the Phen-A/cathode interface. (C) 2008 Elsevier B.V. All rights reserved.. |
| 702. | Toshinori Matsushima, Chihaya Adachi, Enhancing hole transports and generating hole traps by doping organic hole-transport layers with p-type molecules of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, THIN SOLID FILMS, 10.1016/j.tsf.2008.07.008, 517, 2, 874-877, 517, 874-877(2008), 2008.11, We investigated the relationship between the hole-transport and hole-trap characteristics of N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (alpha-NPD) doped with p-type molecules of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)-TCNQ) at various concentrations. The results of our current density-voltage, field-effect transistor, and thermally stimulated current studies revealed that the current densities of hole-only alpha-NPD devices at a certain driving voltage increased in the F(4)-TCNQ concentration region between 0 mol% and 3 mol% due to the generation of free holes while the hole mobilities of the alpha-NPD layers decreased due to an increase in hole-trap concentration and deepened hole-trap energy levels, which were caused by the F(4)-TCNQ doping. The optimized doping concentration of F(4)-TCNQ was 3 mol%, which provided the highest current density for the hole-only device. On the other hand, since the increase in free-hole concentration was overcome by the decrease in hole mobility, the current density of the hole-only device decreased at the F(4)-TCNQ concentration of 4 mol% when compared with the optimized concentration. (C) 2008 Elsevier B.V. All rights reserved.. |
| 703. | Ryuhei Nishiyabu, Nozomi Hashimoto, Ten Cho, Kazuto Watanabe, Takefumi Yasunaga, Ayataka Endo, Kenji Kaneko, Takuro Niidome, Masaharu Murata, Chihaya Adachi, Yoshiki Katayama, Makoto Hashizume, Nobuo Kimizuka, Nanoparticles of Adaptive Supramolecular Networks Self-Assembled from Nucleotides and Lanthanide Ions, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja8058843, 131, 6, 2151-2158, 131, 2151-2158(2009), 2009.02, Amorphous nanoparticles of supramolecular coordination polymer networks are spontaneously self-assembled from nucleotides and lanthanide ions in water. They show intrinsic functions such as energy transfer from nucleobase to lanthanide ions and excellent performance as contrast enhancing agents for magnetic resonance imaging (MRI). Furthermore, adaptive inclusion properties are observed in the self-assembly process: functional materials such as fluorescent dyes, metal nanoparticles, and proteins are facilely encapsulated. Dyes in these nanoparticles fluoresce in high quantum yields with a single exponential decay, indicating that guest molecules are monomerically wrapped in the network. Gold nanoparticles and ferritin were also wrapped by the supramolecular shells. In addition, these nucleotide/lanthanide nanoparticles also serve as scaffolds for immobilizing enzymes. The adaptive nature of present supramolecular nanoparticles provides a versatile platform that can be utilized in a variety of applications ranging from material to biomedical sciences. As examples, biocompatibility and liver-directing characteristics in in vivo tissue localization experiments are demonstrated.. |
| 704. | Masaya Hirade,Hajime Nakanotani ,Reiji Hattori,Akihiro Ikeda,Masayuki Yahiro,Chihaya Adachi, Low threshold blue emission from first-order organic DFB laser using 2,7-bis[4-(N-carbazole)phenylvinyl]-9,9`-spirobifluorene as active gain medium, Mol.Cryst.Liq.Cryst, 504, 1-8, 2009.01. |
| 705. | Tomo Sakanoue,Toru Irie,Chihaya Adachi, Charge separation and transport behavior of a two-dimensional charge sheet at organic donor-acceptor heterointerface, J.Appl.Phys.., 105, 114502, 2009.01. |
| 706. | Daisuke Yokoyama, Akio Sakaguchi, Michio Suzuki, Chihaya Adachi, Horizontal orientation of linear-shaped organic molecules having bulky substituents in neat and doped vacuum-deposited amorphous films, ORGANIC ELECTRONICS, 10.1016/j.orgel.2008.10.010, 10, 1, 127-137, 10、127-137（2009）, 2009.02, Organic amorphous films fabricated by vacuum deposition have been widely used in organic light-emitting devices, making use of their high-performance optical and electrical characteristics and taking advantage of the easy fabrication of pinhole-free thin smooth layers of a desired thickness. However, random orientation in amorphous films often makes it difficult to utilize their best optical and electrical potential. Here the authors demonstrate that the linear-shaped molecules of fluorescent styrylbenzene derivatives are horizontally oriented in organic amorphous films fabricated by conventional vacuum deposition even when the molecules are doped in an isotropic host matrix film. The longer the molecular length is, the larger the anisotropy of the molecular orientation becomes. The weak interaction between adjacent molecules and the linear-shaped molecular structure probably cause the horizontal orientation. The fact that the horizontal molecular orientation occurs on any underlying layers shows the high versatility of the horizontal orientation for various applications. Their findings will provide a new guideline for molecular designs that can be used to improve optical and electrical characteristics of organic optoelectronic devices, such as organic light-emitting diodes and organic laser devices. (C) 2008 Elsevier B.V. All rights reserved.. |
| 707. | Daisuke Yokoyama,Akio Sakaguchi,MIchio Suzuki,Chihaya Adachi, Horizontal orientation of linear-shaped organic molecules having bulky substituents in near and doped vacuum-deposited amorphous films, Org.Electron.., 2009.02. |
| 708. | R.Nishiyabu,N.Hashimoto,T.Cho,K.Watanabe,T.Yasunaga,A.Endo,K.Kaneko,T.Niidome,M.Murata,C.Adachi,Y.Katayama,M.Hashizume,N.Kimuzuka, Nanoparticles of adaptive supramolecular networks self-assembled from nucleotides and lanthanide irons, J.Am.Chem.Soc.., 131, 2151-2158, 2009.03. |
| 709. | Kenji Kawano, Jun Sakai, Masayuki Yahiro, Chihaya Adachi, Effect of solvent on fabrication of active layers in organic solar cells based on poly(3-hexylthiophene) and fullerene derivatives, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 10.1016/j.solmat.2008.11.003, 93, 4, 514-518, 93、514-518（2009）, 2009.04, Investigating the effect of solvent on the fabrication of photo-active layers in bulk heterojunction organic solar cells based on poly(3-hexylthiophene) and [6,6]-phenyl C(61)-butyric acid methyl ester, we found the short-circuit current density (J(SC)) and fill factor (FF) of a cell with a photo-active layer made using materials dissolved in a mixture of o-dichlorobenzene with chloroform to be slightly higher than those of a cell made using the same materials dissolved only in chlorobenzene. Evaluating the absorption spectra, surface morphology, charge mobility, and solubility of photo-active films made using different solvents, we concluded that the higher J(SC) and FF were due to a larger interfacial area between the photo-active materials in the layer. (C) 2008 Elsevier B.V. All rights reserved.. |
| 710. | Tung-Huei Ke,Robert Gehlhaar,Chih-Hsin Chen,Jiann-T'suen Lin,Chung-Chih Wu,Chihaya Adachi, High efficiency blue light emitting unipolar transistor incorporating multifunctional electrodes, Appl.Phys.Lett.., 94, 153307, 2009.04. |
| 711. | Kenji kawano,Jun Sakai,Masyuki Yahiro,Chihaya Adachi, Efffect of solvent on fabrication of active layers in organic solar cells based on poly(3-hexylthiophene)and fullerene derivatives, Sol.Energy Mater.Sol.Cells., 2009.04. |
| 712. | Hajime Kubota,Msatoshi Saito,Hiroaki Nakamura, Chihaya Adachi, Tunig of threshold voltage by interfacial carrier doping in organic single crystal ambipolar light-emittting transistors and their bright electroluminescence, Appl.Phys.Lett.., 95, 103307, 2009.05. |
| 713. | Ayataka Endou,Chihaya Adachi, Photoluminescence characteristics of tris(2-phenylquinoline)iridium (Ⅲ)dispersed in an iridium complex host layer, Chem.Phys.Lett.., 483, 224-226, 2009.05. |
| 714. | Ayataka Endou,Chihaya Adachi, Photoluminescence characteristics of tris(2-phenylquinoline)iridium (Ⅲ)dispersed in an iridium complex host layer, Chem.Phys.Lett.., 483, 224-226, 2009.05. |
| 715. | Ayataka Endou,Chihaya Adachi, Photoluminescence characteristics of tris(2-phenylquinoline)iridium (Ⅲ)dispersed in an iridium complex host layer, Chem.Phys.Lett.., 483, 224-226, 2009.05. |
| 716. | Ryota Kabe,Hajime Nakanotani,Tomo Sakanoue,Masayuki Yahiro,Chihaya Adachi, Effect of molecular morpholgy on amplified spontaneous emission of bis-styrylbenzene derivatives, Adv.Mater.., 40, 4034-4038, 2009.05. |
| 717. | Guoliang Mao, Akihiro Orita, Larysa Fenenko, Masayuki Yahiro, Chihaya Adachi, Junzo Otera, Blue emitting fluorophores of phenyleneethynylenes substituted by diphenylethenyl terminal groups for organic light-emitting diodes, MATERIALS CHEMISTRY AND PHYSICS, 10.1016/j.matchemphys.2008.12.015, 115, 1, 378-384, 115, 378-384(2009), 2009.05, Phenyteneethynylene motifs substituted by diphenylethenyl groups at both ends were prepared successfully by use of double elimination protocol of P-substituted sulfones for introducing phenyleneethynylene arrays followed by Wittig-Horner reaction for introducing diphenylethenyl moiety. The hybrid blue fluorophores exhibited strong emission even in the solid-state films (Phi(F) >= 0.60) while, in CHCl3 solution, incorporation of substituents on the central phenylene unit significantly enhanced emission efficiency UP to Phi(F) = 0.57. The OLED devices with use of these blue fluorophores as an emitting material provided maximum external quantum efficiency of eta(ext) = 2.4%. (C) 2009 Elsevier B.V. All rights reserved.. |
| 718. | N.Matsumoto,T.Miyazaki,M.Nishiyama,C.Adachi, Efficient deep-blue organic light-emitting diodes based on 9,9-bis(4-biphenyly)fluorene derivatives, J.Phys.Chem.C., 113, 6261-6266, 2009.05. |
| 719. | Gouliang Mao,Akihiro Orita,Larysa Feneko,Masayuki Yahiro, Chihaya Adachi,Junzo Otera, Blue emitting fluorophores of phenyleneethnylense substituted by diphenylethenyl terminal groups for organic light emitting diodes, Mat.Chem.Phys.., 115, 378-384, 2009.05. |
| 720. | Daisuke Yokoyama, Masato Moriwake, Chihaya Adachi, Spectrally narrow emissions at cutoff wavelength from edges of optically and electrically pumped anisotropic organic films, JOURNAL OF APPLIED PHYSICS, 10.1063/1.2942401, 103, 12, J.Appl.Phys.103,123104(2008) J.Appl.Phys.104,039909(2008), 2008.06, The authors investigated the characteristics of spectrally narrow emissions at the cutoff wavelength from the edges of optically and electrically pumped organic semiconductor films. They estimated the optical properties of 4,4(')-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) films using variable angle spectroscopic ellipsometry, revealing that the BSB-Cz films have uniaxial anisotropy and that BSB-Cz molecules lie nearly parallel to substrate surfaces. The authors discuss here the spectral changes in the edge emissions from neat BSB-Cz and tris(8-hydroxyquinoline)aluminum (Alq(3)) films of 15 different thicknesses under continuous-wave (cw) optical excitation. The spectrally narrow emissions of transverse electric (TE) and transverse magnetic (TM) modes were observed. The authors showed that the peak wavelengths of these emissions varied according to the cutoff wavelengths of asymmetric slab waveguides and that their spectral widths changed depending on the angular dispersion of the Fabry-Perot interferometer composed of the organic film and its interfaces. The edge emissions from the BSB-Cz films had narrower bands than those from the Alq(3) films and increased with a superlinear dependence on the stripe length of the excitation area, indicating the occurrence of light amplification under cw optical excitation. Finally, the authors demonstrate spectrally narrow emissions from the edges of electrically pumped organic light-emitting diodes (OLEDs) having a fine line-shaped waveguide structure with a silver metal cladding layer. Narrow emissions of TE mode were observed, and the peak wavelengths of the emission spectra corresponded well to the cutoff wavelength of the waveguide with the silver cladding layer. In addition to the narrow emissions, the authors observed some intriguing phenomena suggestive of the occurrence of light amplification in OLEDs under electrical pumping. (C) 2008 American Institute of Physics.. |
| 721. | Y.Shibano,H.Imahori,C.Adachi, Organic Thin-Film Solar Cell Using Electron-Donating Perylene Tetracarboxylic Acid Derivatives, J.Phys.Chem.C., 113, 15454-15466, 2009.07. |
| 722. | Takafumi Izawa, Hiroki Mori, Yusuke Shinmura, Masahito Iwatani, Eigo Miyazaki, Kazuo Takimiya, Hsio-Wen Hung, Masayuki Yahiro, Chihaya Adachi, Molecular Modification of 2,7-Diphenyl[1]benzothieno[3,2-b]benzothiophene (DPh-BTBT) with Diarylamino Substituents: From Crystalline Order to Amorphous State in Evaporated Thin Films, CHEMISTRY LETTERS, 10.1246/cl.2009.420, 38, 5, 420-421, 38,420-421, 2009.05, Introduction of diarylamino substituents on 2,7-diphenyl[1]-benzothieno[3,2-b]benzothiophene (DPh-BTBT) caused morphological change in the evaporated thin-film state: from highly crystalline films with edge-on molecular orientation for DPh-BTBT to amorphous films for the diarylamino derivatives. The former was unsuitable as a hole-transporting layer in organic light-emitting diodes (OLEDs), whereas the latter acted as a superior hole-transporting layer in multilayered OLEDs.. |
| 723. | Hajime Nakanotani,Masatoshi Saito,Hiroaki nakamura,Chihaya Adachi, Highly balanced ambipolar mobilities with intense electroluminescence in field-effect transistors based on organic single crystal oligo(p-phenylenevinylene)derivatives, Appl.Phys.Lett.., 95, 033308, 2009.07. |
| 724. | Denghui Xu Ke,Chihaya Adachi, Organic light-emitting diode having liquid emitting layer, Appl.Phys.Lett.., 95, 053304, 2009.08. |
| 725. | Tung-Huei Ke,Robert Gehlhaar,Chih-Hsin Chen,Jiaan-T Lin,Chung-Chih Wu,Chihaya Adachi, Single molecule color controllable light emitting organic field effect transistors for white light emission with high color stability, Appl.Phys.Lett.., 95, 063303, 2009.08. |
| 726. | Korefumi Kubota,Takuji Kato, Chihaya Adachi, Control of the molecular orientation of a 2,2`-bithiophene-9,9`-dioctylfluorene copolymer by laser-annealing and subsequent enhancement of FET characteristics, Appl.PHys.Lett.., 95, 073303, 2009.08. |
| 727. | Ayataka Endo,Mai Ogasawara,Atsushi Takahashi,Disuke Yokoyama,Yoshimine Katou,Chihaya Adachi, Thermally activated delayed fluorescence from Sn4+-porphyrin comlexes and their application to organic light emitting diodes-a novel mechanism for electroluminescence, Adv.Mater, 21, 4802-4906, 2009.08. |
| 728. | Robert Gehlhaar, Masayuki Yahiro, Chihaya Adachi, Finite difference time domain analysis of the light extraction efficiency in organic light-emitting field-effect transistors, JOURNAL OF APPLIED PHYSICS, 10.1063/1.2968132, 104, 3, 104,033116(2008), 2008.08, The authors report on three-dimensional numerical optical simulations of the emission outcoupling efficiency in light-emitting devices with a field-effect carrier transport. The finite difference time domain method is applied to organic thin film structures on a silicon substrate with metal and metal oxide electrodes. Simulations are performed for Au, Ag, and indium tin oxide electrodes in a bottom gate, bottom contact geometry. Additional attention is paid to the dependence on electrode thickness and contact shape. We demonstrate that in unipolar driven devices with Si gate, silicon dioxide insulator, and 40 nm thick organic films, the maximum outcoupling efficiency is below 10%. This value can be increased by the implementation of a metal reflecting layer on the Si substrate. In further studies, the emission efficiency in the ambipolar regime is investigated. The result presents the dependence of light extraction on the light source-electrode distance for rectangular and wedge shaped contacts. (C) 2008 American Institute of Physics.. |
| 729. | Korefumi Kubota, Takuji Kato, Chihaya Adachi, Control of the molecular orientation of a 2,2(')-bithiophene-9,9-dioctylfluorene copolymer by laser annealing and subsequent enhancement of the field effect transistor characteristics, APPLIED PHYSICS LETTERS, 10.1063/1.3211125, 95, 7, Appl. Phys. Lett (accepted), 2009.08, We controlled the orientation of a 2,2(')-bithiophene-9,9-dioctylfluorene (F8T2) copolymer spin-coated film on a polycarbonate substrate using a laser-annealing technique and demonstrated an enhancement of the field-effect transistor characteristics. We used a semiconductor laser, having a lasing wavelength of lambda=405 nm, with a small spot size of 400 nm. Using polarizing optical microscopy and x-ray diffraction analysis, we confirmed enhancement of the orientation of the molecular chains of F8T2, along the laser scanning direction. Following laser annealing, the field-effect hole mobility resulted in a value of mu=1.6x10(-3) cm(2)/V s, which is about three times higher than that of the unannealed sample.. |
| 730. | Kenji Kawano, Chihaya Adachi, Evaluating Carrier Accumulation in Degraded Bulk Heterojunction Organic Solar Cells by a Thermally Stimulated Current Technique, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.200901573, 19, 24, 3934-3940, 3934-3940, 2009.12, Here, the initial photo-degradation of encapsulated P3HT:PCBM bulk heterojunction organic solar cells is investigated. The degraded device is recovered by thermal annealing treatment. Thermally stimulated current measurements reveal that the cause of photo-degradation is carrier accumulation and that the degraded organic solar cell has two broad trap levels, of 0.71 and 0.81 eV. These traps are independent of the thickness of the photoactive layers, the mixing ratio of the photoactive materials and the cathode materials. In addition, it is confirmed that there is a close relationship between the degree of degradation and the amount of accumulated charge carriers.. |
| 731. | F. Becker, M. Langner, H. Froeb, V. G. Lyssenko, K. Leo, C. Adachi, Dependence of polarization splitting on mode tuning in microcavities, APPLIED PHYSICS LETTERS, 10.1063/1.3263145, 95, 19, (in press), 2009.11, We present an in-depth analysis of the angle and mode tuning dependence of the polarization splitting in detuned organic microcavities. The system consists of highly reflecting dielectric mirrors comprising a continuous wedge-shaped cavity layer of 4,4'-bis(N-carbazole)-biphenyl, doped with 2 wt % of 4,4'-bis[(N-carbazole)styryl]-biphenyl as the active material. By varying the measurement position across the sample, we shift the resonant mode with respect to the center of the cavity stop band. Starting from small detunings, the splitting value increases non-linearly up to 58 meV, when the resonant modes reach the stop band edge. We compare this behavior with results from transfer matrix calculations and theoretical predictions. (c) 2009 American Institute of Physics. |
| 732. | Daisuke Yokoyama,Akio Sakaguchi,Michio Suzuki,Chihaya Adachi, Enhancement of electron transport by horizontal molecular orientation of oxadiazole planar molecules in organic amorphous films, Appl.Phys.Lett., 95, 243303, 2009.12. |
| 733. | Hajime Nakanotani,Masatoshi Saitou,Hiroaki Nakamura,Chihaya Adachi, Emission color tuning in ambipolar organic single crystal field-effect transistors by dye-doping, Adv.Funct.Mat, 2010.04. |
| 734. | Manabu Nakata,Kenji kawano, Mao Yasumatsu,Masayuki Yahiro,Chihaya Adachi, Formation of Organic Nanodots with a Minimum Diameter of 40 nm Using Conventional Vacuum Vapor Deposition, Appl.Ohys.Exp.., 3, 055201, 2010.04. |
| 735. | Naoki Matsumoto,Chihaya Adachi, Exciplex formations at HTL/Alq3 interface in organic light-emitting diode: influence of electron-hole recombination zone and electric field, J.Phys.Chem.C., 114(10), 4652-4658, 2010.04. |
| 736. | Joerg Frischeisen ,Daisuke Yokoyama,Chihaya Adachi, Wolfgang Bruetting, Determination of molecular dipole orientation in fluorescent organic thin films by photoluminescence measurement, Appl.Phys.Lett., 96, 073302, 2010.04. |
| 737. | Daisuke Yokoyama,Chihaya Adachi, In situ real-time spectroscopic ellipsometry measurement for investigation of molecular orientation in organic amorphous multilayer structures, J.Appl.Phys., 2010.05. |
| 738. | Ayataka Endo,Chihaya Adachi, Photoluminescence characteristics of organic host materials with wide energy gaps for organic electrophosphorecent devices, Jpn.JAppl..Phys., 49, 050205, 2010.05. |
| 739. | Kenji Kawano,Chihaya Adachi, Reduced initial degradation of bulk heterojunction organic solar cells by incorporation of stacked fullerene and lithium fullerene interlayers, Appl.Phys.Lett.., 96, 053307, 2010.05. |
| 740. | Hajime Nakanotani,Chihaya Adachi, Organic light-emitting diodes containing multilayers of organic single crystals, Appl.Phys.Lett.., 96, 053301, 2010.05. |
| 741. | Takatoshi Nishio, Makoto Kashiwagi,Koji Miyazaki,Masayuki Yahiro,Chihaya Adachi, Preparation under high humidity conditions of nano-porous polymer film with 80 nm minimum pore size, Appl.Phys.Exp.., 3, 025201, 2010.05. |
| 742. | Daisuke Yokoyama ,Yousuke Setoguchi,Akiko Sakaguchi,Michio Suzuki,Chihaya Adachi, Orientation control of linear-shaped molecules in vacuum-deposited organic amorphous films and its effect on carrier mobilities, Adv.Funct.Mat.., 20, 386-391, 2010.05. |
| 743. | Kentaro Harada, Mao Sumino, Chihaya Adachi, Saburo Tanaka, Koji Miyazaki, Improved thermoelectric performance of organic thin-film elements utilizing a bilayer structure of pentacene and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F-4-TCNQ), APPLIED PHYSICS LETTERS, 10.1063/1.3456394, 96, 25, 253304, 2010.06, We demonstrate an improved thermoelectric performance of small molecular thin films fabricated by thermal deposition of pentacene as a p-type conduction layer. To enhance the performance, a bilayer structure composed of an intrinsic pentacene layer and an acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane layer is utilized as the prototype thermoelectric element. With the bilayer structure, the electrical conductivity reaches 0.43 S/cm, exhibiting a positive Seebeck coefficient of about 200 mu V/K. We thus obtain a high power factor of 2.0 mu W/mK(2) with an optimized layer thickness. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456394]. |
| 744. | Kenji Muneuchi, Masaomi Sasaki, Hiroyuki Sasabe, Chihaya Adachi, 3,6-Diarylcarbazole Derivatives as a Host Material in Organic Electrophosphorescent Diodes, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.1143/JJAP.49.080208, 49, 8, 080208, 2010.08, We synthesized 3,6-diarylcarbazole (CBZ) derivatives and investigated their thin-film optical (i e, absorption, fluorescence and phosphorescence) properties and electroluminescence characteristics We fabricated phosphorescent organic light-emitting diodes (OLEDs) employing CBZ derivatives as the host and fac-tris(2-phenypyridine)iridium [Ir(ppy)(3)] as the guest at a doping concentration of 6 wt % These devices exhibited maximum external quantum efficiencies (eta(ext)) in the range 1 to 11%, depending on the host In particular, the OLED with CBZ7 as the host exhibited the highest eta(ext) of 11 2% and a maximum power conversion efficiency (eta(energy)) of 25Im/W (C) 2010 The Japan Society of Applied Physics. |
| 745. | Yousuke Setoguchi, Chihaya Adachi, Suppression of roll-off characteristics of electroluminescence at high current densities in organic light emitting diodes by introducing reduced carrier injection barriers, JOURNAL OF APPLIED PHYSICS, 10.1063/1.3488883, 108, 6, 64516, 064516, 2010.09, We experimentally investigated suppression of the roll-off characteristics of the electroluminescence efficiency at high current densities in organic light emitting diodes (OLEDs). To increase exciton density, we propose a nonheterostructure OLED that consists of a single emitting layer of 4,4'-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) and layers locally with doped donors/acceptors on the cathode and anode sides. The OLED exhibited suppression of the roll-off characteristics at high current densities over 100 A/cm(2) with balanced bipolar injection and transport, resulting in the high exciton density of 10(24) cm(-3) s(-1). Furthermore, amplified spontaneous emission with a relatively low threshold of E(th)=24 mu J/cm(2) was obtained by optically pumping the single-layer device. However, to realize electrical excitation it was necessary to reduce the lasing threshold by two orders of magnitude or to inject a 100 times higher current density. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488883]. |
| 746. | Zhonglian Wu, Benhu Fan, Feng Xue, Chihaya Adachi, Jianyong Ouyang, Organic molecules based on dithienyl-2,1,3-benzothiadiazole as new donor materials for solution-processed organic photovoltaic cells, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 10.1016/j.solmat.2010.07.017, 94, 12, 2230-2237, 2230-2237, 2010.12, Polymers based on dithienyl-2,1,3-benzothiadiazole (TBT) have received strong attention as the donor materials of polymer photovoltaic cells (PVs), since they can have a low band gap. But soluble small organic molecules based on TBT have been rarely studied. This paper reports the synthesis of two small organic molecules based on TBT and their application as the donor materials of solution-processed bulk heterojunction organic photovoltaic cells (OPVs). These compounds were soluble in common organic solvents, such as chloroform, chlorobenzene and tetrahydrofuran. They have band gaps comparable to poly(3-hexylthiophene) (P3HT) and lower HOMO and LUMO (HOMO: highest occupied molecular orbital. LUMO: lowest unoccupied molecular orbital) levels than P3HT. These molecules and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were used as the donors and acceptor to fabricate bulk heterojunction OPVs through solution processing. After optimization of the experimental conditions, power conversion efficiency (PCE) of 0.66% was achieved on the solution-processed OPVs under AM 1.5G, 100 mW cm(-2) illumination. (C) 2010 Elsevier B.V. All rights reserved.. |
| 747. | Kentaro Harada, Tomohiko Edura and Chihaya Adachi, Nanocrystal growth and improved performance of small molecule bulk heterojunction solar cells composed of a blend of chloroaluminum Phthalocyanine and C70, Appl. Phys. Exp., 10.1143/APEX.3.121602, 3, 121602, 2010.12. |
| 748. | Masaya Hirade, Hajime Nakanotani, Masayuki Yahiro, Chihaya Adachi, Formation of Organic Crystalline Nanopillar Arrays and Their Application to Organic Photovoltaic Cells, ACS APPLIED MATERIALS & INTERFACES, 10.1021/am100915s, 3, 1, 80-83, 80-83, 2011.01, To enhance the performance of organic photovoltaic (OPV) preparation of organic nanometer-sized pillar arrays is fascinating because a significantly large area of a donor/acceptor heterointerface having continuous conduction to both anode and cathode electrodes can be realized. In this study, we grew cupper phthalocyanine (CuPc) crystalline nanopillar arrays by conventional thermal gradient sublimation technique using a few-nanometer-sized trigger seeds composed of a CuPc and 3,4,9,10-perylene-thermal carboxylic-dianhydride (PTCDA) stacked layer. We optimized the pillar density by tuning crystal growth condition in order to apply it to OPV cells.. |
| 749. | Hajime Nakanotani, Hayato Kakizoe, Chihaya Adachi, Highly conductive interface between a rubrene single crystal and a molybdenum oxide layer and its application in transistors, SOLID STATE COMMUNICATIONS, 10.1016/j.ssc.2010.10.004, 151, 1, 93-96, 93-96, 2011.01, The formation of interfacial hole carriers between a rubrene single crystal and a 2 nm-thick molybdenum oxide layer resulted in the formation of a highly conductive Interface with a high electrical conductivity of 0 16 S/cm and a very small activation energy of 003 eV This highly conductive interface enabled charge injection and accumulation of a high drain current in the recombination zone in ambipolar transistors resulting in a significant reduction of the driving voltage with high balanced hole and electron mobilities of 11 and 0 5 cm(2)/Vs respectively (C) 2010 Elsevier Ltd All rights reserved. |
| 750. | Jorg Frischeisen, Bert Scholz, Benedikt Arndt, Tobias Schmidt, Robert Gehlhaar, Chihaya Adachi and Wolfgang Brutting, Strategies for enhanced light extraction from surface plasmons in organic light-emitting diodes, J. Photonics for Energy, 10.1117/1.3523314, 1, 011004, 2011.01. |
| 751. | Shuzo Hirata, Korefumi Kubota, Heo Hyo Jung, Osamu Hirata, Kenichi Goushi, Masayuki Yahiro, Chihaya Adachi, Improvement of Electroluminescence Performance of Organic Light-Emitting Diodes with a Liquid-Emitting Layer by Introduction of Electrolyte and a Hole-Blocking Layer, ADVANCED MATERIALS, 10.1002/adma.201003505, 23, 7, 889-+, 889-893, 2011.02, Organic light-emitting diodes containing a liquid-emitting layer that exhibit improved external electroluminescence quantum efficiency (Phi(EL)) and maximum luminance are presented. Doping the liquid-emitting layer with an electrolyte significantly decreases the turn-on voltage for electroluminescence. Insertion of a TiO(2) hole-blocking layer between the liquid-emitting layer and indium tin oxide cathode improves Phi(EL).. |
| 752. | Ayataka Endo, Keigo Sato, Kazuaki Yoshimura, Takahiro Kai, Atsushi Kawada, Hiroshi Miyazaki, Chihaya Adachi, Efficient up-conversion of triplet excitons into a singlet state and its application for organic light emitting diodes, APPLIED PHYSICS LETTERS, 10.1063/1.3558906, 98, 8, 083302, 2011.02, A material possessing a very small energy gap between its singlet and triplet excited states, Delta E1-3, which allows efficient up-conversion of triplet excitons into a singlet state and leads to efficient thermally activated delayed fluorescence (TADF), is reported. The compound, 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a] carbazole-11-yl)-1,3,5-triazine, breaks the restriction of a large energy gap, with a Delta E1-3 of just 0.11 eV, while maintaining a high fluorescent radiative decay rate (k(r) similar to 10(7)). The intense TADF provides a pathway for highly efficient electroluminescence. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3558906]. |
| 753. | Hirotake So, Hirofumi Watanabe, Masayuki Yahiro, Yu Yang, Yuji Oki and Chihaya Adachi, highly photostable distributed-feedback polymer waveguide blue laser using spirobifluorene derivatives, Opt. Mat., 33, 6, 755-758, 2011.04. |
| 754. | Daisuke Yokoyama, Hisahiro Sasabe, Yukio Furukawa, Chihaya Adachi, Junji Kido, Molecular Stacking Induced by Intermolecular C-H center dot center dot center dot N Hydrogen Bonds Leading to High Carrier Mobility in Vacuum-Deposited Organic Films, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.201001919, 21, 8, 1375-1382, 1375-1382, 2011.04, Simple bottom-up fabrication processes for molecular self-assembly have been developed for the construction of higher-order structures using organic materials, and have contributed to maximization of the potential of organic materials in chemical and bioengineering. However, their application to organic thin-film devices such as organic light-emitting diodes have not been widely considered because simple fabrication of a solid film containing an internal self-assembly structure has been regarded as difficult. Here it is shown that the intermolecular C-H center dot center dot center dot N hydrogen bonds can be simply formed even in vacuum-deposited organic films having flat interfaces. By designing the molecules containing pyridine rings properly for the intermolecular interaction, one can control the molecular stacking induced by the intermolecular hydrogen bonds. It is also demonstrated that the molecular stacking contributes to the high carrier mobility of the film. These findings provide new guidelines to improve the performance of organic optoelectronic devices and open up the possibilities for further development of organic devices with higher-order structures.. |
| 755. | Satria Zulkarnaen Bisri, Taishi Takenobu, Kosuke Sawabe, Satoshi Tsuda, Yohei Yomogidao, Takeshi Yamao, Shu Hotta, Chihaya Adachi, Yoshihiro Iwasa, p-i-n Homojunction in Organic Light-Emitting Transistors, ADVANCED MATERIALS, 10.1002/adma.201004572, 23, 24, 2753-2758, 2753-2758, 2011.06, A new method for investigating light-emitting property in organic devices is demonstrated. We apply the ambipolar light-emitting transistors (LETS) to directly observe the recombination zone, and find a strong link between the transistor performance and the zone size. This finding unambiguously indicates that the light emission comes from the electric-field-induced p-i-n homojunction in ambipolar LETs.. |
| 756. | Takuji Kato, Chikako Origuchi, Masato Shinoda, Chihaya Adachi, Organic Electrodes Consisting of Dianthratetrathiafulvalene and Fullerene and Their Application in Organic Field Effect Transistors, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.1143/JJAP.50.050202, 50, 5, 50202, 050202, 2011.05, A double layer of dianthratetrathiafulvalene (DATTF) and fullerene (C-60) on an n(++)-Si wafer pretreated with n-octyltrichlorosilane exhibited a high electrical conductivity of sigma = 0.12 S/cm and was used as source-drain electrodes in organic field effect transistors (OFETs). A simplified OFET device architecture composed of an organic semiconducting active layer and an organic electrode layer was easily fabricated by successive vacuum deposition of organic donor and acceptor layers. It was confirmed that this device configuration is applicable for both p-and n-type FET operation. (C) 2011 The Japan Society of Applied Physics. |
| 757. | Joerg Frischeisen, Daisuke Yokoyama, Ayataka Endo, Chihaya Adachi, Wolfgang Bruetting, Increased light outcoupling efficiency in dye-doped small molecule organic light-emitting diodes with horizontally oriented emitters, ORGANIC ELECTRONICS, 10.1016/j.orgel.2011.02.005, 12, 5, 809-817, 809-817, 2011.05, Small molecule organic light-emitting diodes (SM-OLEDs) are efficient large area light sources facing their market entry. However, a low light outcoupling efficiency of typically 20% still strongly limits device performance. Here, we highlight the potential of employing dye-doped emission layers with emitting molecules having horizontally oriented transition dipole moments. The effect of molecular orientation is explained by studying optical simulations that distinguish between horizontal and vertical dipole orientation. In addition, an experimental method that enables straightforward determination of dipole orientation in guest-host systems is presented and used for the analysis of two materials that are very similar except for their orientation. By measuring the external electroluminescence quantum efficiency of SM-OLEDs based on these materials, evidence is found that a mainly horizontal dipole orientation enhances light outcoupling by around 45%. Furthermore, the effect of orientation in SM-OLEDs offers many additional benefits concerning stack design and has fundamental implications for material choice. (C) 2011 Elsevier B.V. All rights reserved.. |
| 758. | Daisuke Matsuo, Xin Yang, Akiko Hamada, Kyo Morimoto, Takuji Kato, Masayuki Yahiro, Chihaya Adachi, Akihiro Orita, Junzo Otera, Fluoro-substituted Phenyleneethynylenes Acetylenic n-Type Organic Semiconductors, CHEMISTRY LETTERS, 10.1246/cl.2010.1300, 39, 12, 1300-1302, 1400, 2010.12, Fluoro-substituted phenyleneethynylenes are synthesized by Sonogashira coupling and acetylide-nucleophilic substitution of fluorobenzenes Fluoro-substitution of benzenes enables deep LUMO potential, and CF3-substitution provides high electron mobility in deposited film (mu = 5 5 x 10(-2) cm(2) V-1 s(-1)). |
| 759. | Joerg Frischeisen, Quan Niu, Robert Gehlhaar, Giuseppe Scarpa, Chihaya Adachi, Paolo Lugli, and Wolfgang Brutting, Light extractionfrom surface plasmons and waveguide modes with nanoimprinted gratings in organic light-emitting diodes, Optical Express, 10.1364/OE.19.0000A7, 19, S1, A7, 2011.05. |
| 760. | Makoto Kashiwagi, Shuzo Hirata, Kentaro Harada, Yanqiong Zheng, Koji Miyazaki, Masayuki Yahiro, Chihaya Adachi, Enhanced figure of merit of a porous thin film of bismuth antimony telluride, APPLIED PHYSICS LETTERS, 10.1063/1.3543852, 98, 2, 23114, 023114, 2011.01, A porous thin film of Bi(0.4)Te(3)Sb(1.6) with an enhanced figure of merit of 1.8 at room temperature was fabricated by flash evaporation on an alumina substrate containing hexagonally arranged nanopores with an average diameter of 20 nm, separated by an average distance of 50 nm. The thermal conductivity was significantly reduced compared with standard Bi(0.4)Te(3)Sb(1.6) films to 0.25 W/(m.K) with no major decrease in either the electrical conductivity (398 S/cm) or the Seebeck coefficient (198 mu V/K). The reduction in thermal conductivity was rationalized using a model for the full distribution of the phonon mean free path in the film. (c) 2011 American Institute of Physics. [doi:10.1063/1.3543852]. |
| 761. | Masatsugu Taneda, Takuma Yasuda, Chihaya Adachi, Horizontal Orientation of a Linear-Shaped Platinum(II) Complex in Organic Light-Emitting Diodes with a High Light Out-Coupling Efficiency, APPLIED PHYSICS EXPRESS, 10.1143/APEX.4.071602, 4, 7, 071602, 2011.07, A linear-shaped phosphorescent platinum(II) complex that adopts a horizontal orientation in amorphous films was synthesized. The complex possesses a photoluminescence quantum efficiency of Phi(PL) = 50 +/- 3% in thin films with the host of m-biscarbazolylbenzene and 4,4'-bis(N-carbazolyl)biPhenyl. Polarized emission from the edge of these thin films confirmed the horizontal orientation of the complex within them. An organic light-emitting diode containing the complex possessed a maximum external quantum efficiency of eta(EQE) = 15.8 +/- 3%. The light out-coupling efficiency of the device was estimated to be at least 4 = 32 +/- 3%, which was ascribed to the horizontal orientation of the complex. (C) 2011 The Japan Society of Applied Physics. |
| 762. | Masatsugu Taneda, Takuma Yasuda, and Chihaya Adachi, Horizontal Orientation of a Linear-Shaped Platinum(II) Complex in Organic Light-Emitting Diodes with a High Light Out-Coupling Efficiency, Applied Physics Express, 10.1143/APEX.4.071602, 4, 071602, 2011.06. |
| 763. | Masakazu Ohkita, Ayataka Endo, Kimihiro Sumiya, Hajime Nakanotani, Takanori Suzuki, and Chihaya Adachi, Photophysical characteristics of 4,4’-bis(N-carbazolyl)tolan derivatives and their application in organic light emitting diodes, Journal of Luminescence, 10.1016/j.jlumin.2011.01.028, 131, 7, 1520-1524, 2011.07. |
| 764. | Hizuru Nakajima, Yukiko Okuma, Kazuhiro Morioka, Mayo Miyake, Akihide Hemmi, Tatsuya Tobita, Masayuki Yahiro, Daisuke Yokoyama, Chihaya Adachi, Nobuaki Soh, Koji Nakano, Shuhua Xue, Hulie Zeng, Katsumi Uchiyama, Toshihiko Imato, An integrated enzyme-linked immunosorbent assay system with an organic light-emitting diode and a charge-coupled device for fluorescence detection, JOURNAL OF SEPARATION SCIENCE, 10.1002/jssc.201100429, 34, 20, 2906-2912, 2906-2912, 2011.10, A fluorescence detection system for a microfluidic device using an organic light-emitting diode (OLED) as the excitation light source and a charge-coupled device (CCD) as the photo detector was developed. The OLED was fabricated on a glass plate by photolithography and a vacuum deposition technique. The OLED produced a green luminescence with a peak emission at 512 nm and a half bandwidth of 55 nm. The maximum external quantum efficiency of the OLED was 7.2%. The emission intensity of the OLED at 10 mA/cm(2) was 13 mu W (1.7 mW/cm(2)). The fluorescence detection system consisted of the OLED device, two band-pass filters, a five microchannel poly(dimethylsiloxane) (PDMS) microfluidic device and a linear CCD. The fluorescence detection system was successfully used in a flow-based enzyme-linked immunosorbent assay on a PDMS microfluidic device for the rapid determination of immunoglobulin A (IgA), a marker for human stress. The detection limit (S/N = 3) for IgA was 16.5 ng/mL, and the sensitivity was sufficient for evaluating stress. Compared with the conventional 96-well microtiter plate assay, the analysis time and the amounts of reagent and sample solutions could all be reduced.. |
| 765. | Takuji Kato, Mao Yasumatsu, Chikako Origuchi, Kyoji Tsutsui, Yasukiyo Ueda, Chihaya Adachi, High Carrier Mobility of 3.8 cm(2) V-1 s(-1) in Polydiacetylene Thin Films Polymerized by Electron Beam Irradiation, APPLIED PHYSICS EXPRESS, 10.1143/APEX.4.091601, 4, 9, 91601, 091601, 2011.09, The highest carrier mobility of polydiacetylene (PDA) thin films in field-effect transistors has been limited to less than 0.8cm(2) V-1 s(-1), although the main chain conduction should show higher carrier mobility potentially. We revealed that the cause of the low carrier mobility is due to the presence of local upheaval regions generated by the volume change through the polymerization process of diacetylene monomers. In order to suppress the occurrence of the upheaval regions, we found that electron beam (EB) irradiation is effective, resulted in the highest carrier mobility of mu(max) = 3.8 cm(2) V-1 s(-1). (C) 2011 The Japan Society of Applied Physics. |
| 766. | Toshiharu Arai, Kenichi Goushi, Hiroko Nomura, Tomohiko Edura, Chihaya Adachi, Two-dimensional orientation control of organic semiconducting amorphous films by mechanical brushing, APPLIED PHYSICS LETTERS, 10.1063/1.3608315, 99, 5, 053303, 2011.08, We demonstrate that horizontally oriented organic semiconducting molecules in amorphous films can be oriented uniaxially by mechanical brushing. The absorption of polarized light in the direction parallel to the brushing direction was higher than the absorption in the perpendicular direction. Thus, simultaneous uniaxial and in-plane molecular orientation in amorphous films was realized by brushing. In addition, we demonstrate a polarized electroluminescence from the films treated by mechanical brushing. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3608315]. |
| 767. | Zhonglian Wu, Aiyuan Li, Benhu Fan, Feng Xue, Chihaya Adachi, Jianyong Ouyang, Phenanthrene-functionalized 3,6-dithiophen-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-diones as donor molecules for solution-processed organic photovoltaic cells, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 10.1016/j.solmat.2011.05.006, 95, 8, 2516-2523, 2516–2523, 2011.08, 3,6-Dithiophen-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP) based organic molecules and polymers have received strong attention as the donor materials of efficient organic photovoltaic cells (OPVs). This paper reports the synthesis and characterization of two DPP-based organic molecules functionalized with phenanthrene and ethynylphenanthrene and their application as the donor materials of solution-processed OPVs. They have band gaps of 1.6-1.8 eV and appropriate energy levels, and they can be soluble in common organic solvents such as chloroform and tetrahydrofuran. The C C triple bond in ethynylphenanthrene has a strong effect on the structure and properties of molecules. It increases the rigidity of molecule, decreases the solubility in organic solvents, and increases the crystallinity of the active layer and photovoltaic performance of the OPVs. The optimal photovoltaic efficiency of OPVs with ethynylphenanthrene-functionalized DPP is 1.71% under AM 1.5 G illumination (100 mW cm(-2)), more than double of that of the OPVs with phenanthrene-functionalized DPP. (C) 2011 Elsevier By. All rights reserved.. |
| 768. | Takeshi Komino, Hiroko Nomura, Masayuki Yahiro, Kuniaki Endo, Chihaya Adachi, Dependence of the Amplified Spontaneous Emission Threshold in Spirofluorene Thin Films on Molecular Orientation, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp2007717, 115, 40, 19890-19896, 19890–19896, 2011.10, The dependence of the amplified spontaneous emission threshold (E-th) on molecular orientation in vacuum deposited thin films fabricated from diphenyldiamine- and carbazole-substituted spirofluorene derivatives was investigated. The molecular orientations were modified by changing the substrate temperature during deposition and were almost parallel to the substrate at around 300 K in all of the films. The orientation became random in the film containing diphenyldiamine compound at around 380 K, resulting in decreased optical anisotropy. However, for the carbazole compound, the molecular orientation scarcely changed from 300 to 380 K, while the root-mean-square roughness increased from 0.28 to 0.94 nm. E-th approximately doubled for both the films when the optical anisotropy decreased because of the randomization of molecular orientation or when the surface roughness increased.. |
| 769. | Mao Sumino, Kentaro Harada, Masaaki Ikeda, Saburo Tanaka, Koji Miyazaki, Chihaya Adachi, Thermoelectric properties of n-type C-60 thin films and their application in organic thermovoltaic devices, APPLIED PHYSICS LETTERS, 10.1063/1.3631633, 99, 9, 093308, 2011.08, The high performance of n-type organic thin-film thermoelectric elements utilizing a bilayer structure composed of C-60 and Cs2CO3 was demonstrated. By employing an underlying layer, the electrical conductivity and the power factor of the n-type thermoelectric elements were significantly improved, and a maximum power factor of 20.5 mu W m(-1) K-2 at room temperature was demonstrated. In addition, an organic p-n prototype thermovoltaic device was demonstrated. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3631633]. |
| 770. | Masaya Hirade, Chihaya Adachi, Small molecular organic photovoltaic cells with exciton blocking layer at anode interface for improved device performance, APPLIED PHYSICS LETTERS, 10.1063/1.3650472, 99, 15, 153302, 153302, 2011.10, We demonstrate enhanced power conversion efficiency (eta(PCE)) for small molecular-based organic photovoltaic cells with an exciton blocking layer (ExBL) at the anode/donor interface. Although poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) films are widely used as anodic buffer layers, they also act as exciton quenchers. To prevent exciton quenching, we introduced a tris[4-(5-phenyl thiophen-2-yl)phenyl]amine layer between the donor and the PEDOT:PSS layer and clarified its effect. By a combination of dual ExBLs at both the anode and cathode sides, we achieved significantly enhanced short circuit current and eta(PCE) values; the highest eta(PCE) = 5.24% was obtained by optimizing the device parameters. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3650472]. |
| 771. | Shuzo Hirata, Toshiro Tsuji, Yoshimine Kato, Chihaya Adachi, Reversible Coloration Enhanced by Electrochemical Deposition of an Ultrathin Zinc Layer onto an Anodic Nanoporous Alumina Layer, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.201200353, 22, 20, 4195-4201, 2012.10, A productive method is introduced to realize large area color electronic paper (e-paper) with high UV resistance, heat resistance, and good significant bending properties using a color change triggered by reversible electronic change in the device structure. Reversible coloration and decoloration triggered by electrochemical deposition and desorption, respectively, of an ultra-thin zinc (Zn) layer on a thin transparent conductive layer coated on anodic nanoporous alumina has been developed. The deposition of the ultra-thin Zn layer triggers the formation of destructive interference, which leads to coloration. Yellow, magenta, and cyan colors were obtained in the colored state by increasing the NP-Al2O3 layer thickness, based on Bragg diffraction theory. Reflectance of more than 70% and contrast values of more than 7 were obtained, which are nearly equivalent to those of previous e-papers. The color images in these devices also showed high UV resistance, heat resistance, and repeated significant bending endurance. The devices can be fabricated with large areas using low-cost manufacturing processes such as anodic oxidation, and use abundantly available materials. Our proposed device provides low-cost and flexible large area color e-paper for outdoor use.. |
| 772. | Chih-Hao Chang, Ming-Cheng Kuo, Wei-Chieh Lin, Yu-Ting Chen, Ken-Tsung Wong, Shu-Hua Chou, Ejabul Mondal, Raymond C. Kwong, Sean Xia, Tetsuya Nakagawa and Chihaya Adachi, A dicarbazole-triazine hybrid bipolar host material for highly efficient green phosphorescent OLEDs, Journal of Materials Chemistry, 10.1039/C2JM14686J, 22, 3832-3838, 2012.01. |
| 773. | Xiang Dong Luo, Umme Farva, Nguyen Tam Nguyen Truong, Kyung Soo Son, Pei Sheng Liu, Chihaya Adachi, Chinho Park, Synthesis and characterization of CdSe nanocrystals capped with TOPO and pyridine, JOURNAL OF CRYSTAL GROWTH, 10.1016/j.jcrysgro.2011.11.048, 339, 1, 22-30, 22-30, 2012.01, TOPO-capped CdSe nanocrystals with different sizes were synthesized by a slightly modified Peng and Peng's method, and pyridine-capped CdSe nanocrystals were obtained from TOPO-capped CdSe by exchange of TOPO with pyridine. By applying X-ray powder diffraction. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, photoluminescence (PL) and time-resolved PL (TRPL) spectroscopy, structural and optical characteristics of TOPO-capped and pyridine-capped CdSe are studied in detail. Analysis results show that, by exchanging the surface ligand from TOPO to pyridine, the crystalline quality and optical properties of CdSe nanocrystals are improved. During surface ligand exchange, the diameter of CdSe is decreased, which is caused by the loss of surface Cd and Se atoms with leaving TOPO molecules. The TRPL results suggest that the localized optical transitions of pyridine-capped CdSe, which result from defects and impurities existing in the nanocrystals, are suppressed, compared with those from the original TOPO-capped CdSe. The PL blue-shifts of pyridine-capped CdSe are also observed, and the PL and XPS results indicate that, when TOPO is substituted by pyridine, the surface electronic density of CdSe is re-distributed. (C) 2011 Elsevier B.V. All rights reserved.. |
| 774. | Atsushi Wada, QISHENG ZHANG, Takuma Yasuda, Takasu Isao, Shintaro Enomoto, CHIHAYA ADACHI, Efficient Luminescence from a Copper(I) Complex Doped in Organic Light-Emitting Diodes by Suppressing C-H Vibrational Quenching, Chem. Comm., 10.1039/C2CC31509B, 48, 5340-5342, 2012.03. |
| 775. | Qisheng Zhang, Takeshi Komino, Shuping Huang, Shigeyuki Matsunami, Kenichi Goushi, Chihaya Adachi, Triplet Exciton Confinement in Green Organic Light-Emitting Diodes Containing Luminescent Charge-Transfer Cu(I) Complexes, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.201101907, 22, 11, 2327-2336, 2012.06, The temperature dependence of luminescence from [Cu(dnbp)(DPEPhos)]BF4 (dnbp = 2,9-di-n-butylphenanthroline, DPEPhos = bis[2-(diphenylphosphino)phenyl]ether) in a poly(methyl methacrylate) (PMMA) film indicates the presence of long-life green emission arising from two thermally equilibrated charge transfer (CT) excited states and one non-equilibrated triplet ligand center (3LC) excited state. At room temperature, the lower triplet CT state is found to be the predominantly populated excited state, and the zero-zero energy of this state is found to be 2.72 eV from the onset of its emission at 80 K. The tunable emission maximum of [Cu(dnbp)(DPEPhos)]BF4 in various hosts with different triplet energies is explained in terms of the multiple triplet energy levels of this complex in amorphous films. Using the high triplet energy charge transport material as a host and an exciton-blocking layer (EBL), a [Cu(dnbp)(DPEPhos)]BF4 based organic light-emitting diode (OLED) achieves a high external quantum efficiency (EQE) of 15.0%, which is comparable to values for similar devices based on Ir(ppy)3 and FIrpic. The photoluminescence (PL) and electroluminescence (EL) performance of green emissive [Cu(mu I)dppb]2 (dppb = 1,2-bis[diphenylphosphino]benzene) in organic semiconductor films confirmed its 3CT state with a zero-zero energy of 2.76 eV as the predominant population excited state.. |
| 776. | Shuzo Hirata, Hyo Jung Heo, Yuki Shibano, Osamu Hirata, Masayuki Yahiro, Chihaya Adachi, Improved Device Lifetime of Organic Light Emitting Diodes with an Electrochemically Stable pi-Conjugated Liquid Host in the Liquid Emitting Layer, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.1143/JJAP.51.041604, 51, 4, 041604, 2012.04, The device lifetimes of organic light emitting diodes with a liquid emitting layer (liquid OLEDs) were improved by proper combination of host and guest molecules in the liquid emitting layer. The device lifetime strongly depends on the electrochemical stability of radical cations in the liquid emitting layer. The electrochemical stability of the liquid host materials was achieved by the dimerization of the alkyl-substituted carbazole 9,9'-{2[2-(2-methoxyethoxy)ethoxy]ethyl}-3,3'-bis(9H-carbazole) [(TEGCz)(2)]. The use of a guest compound with its highest occupied molecular orbital level higher in energy than that of (TEGCz)(2) is a critical factor for realizing stable electroluminescence performance. A liquid OLED with proper combination of the guest and host materials showed an improved device lifetime of longer than 1 h, which is 100 times longer than that of our previous reports. (C) 2012 The Japan Society of Applied Physics. |
| 777. | Kenichi Goushi, Kou Yoshida, Keigo Sato, Chihaya Adachi, Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion, Nature Photonics, in press, 2012.03, エキサイプレックスと呼ばれる種類の異なる２つの分子の会合体を有機エレクトロルミネッセンス素子（有機EL素子）の発行材料に適応し、電流励起によるエキサイプレックス発光の中では、最も高い外部量子効率が5％を超える世界トップレベルの高効率化の実現に成功した。本成果は低消費電力で環境負荷が少ない有機ELテレビや有機EL照明などの次世代エレクトロニクス分野において、新たな発光分子の設計指針やデバイスの構築への大きな貢献が期待できる。. |
| 778. | Hitoshi Yamamoto, CHIHAYA ADACHI, Michael S. Weaver, Julie J. Brown, Identification of device degradation positions in multi-layered phosphorescent organic light emitting devices using water probes, APPLIED PHYSICS LETTERS, 10.1063/1.4711129, 100, 18, 2012.04. |
| 779. | N. Niimi, H. Mori, E. Miyazaki, I. Osaka, K. takimiya, CHIHAYA ADACHI, [2,2']Bi[naphtho[2,3-b]furanyl]: a versatile organic semiconductor with a furan-furan junction, Chem. Comm., 10.1039/C2CC31960H, 48, 5892-5894, 2012.04. |
| 780. | Tetsuya Nakagawa, Sung-Yu Ku, Ken-Tsung Wong, CHIHAYA ADACHI, Electroluminescence Based on Thermally Activated Delayed Fluorescence Generated by a Spirobifluorene Donor-Acceptor Structure, Chem. Comm., 10.1039/C2CC31468A, 48, 9580, 2012.04. |
| 781. | Jun Y. Kim, Daisuke Yokoyama, Chihaya Adachi, Horizontal Orientation of Disk-like Hole Transport Molecules and Their Application for Organic Light-Emitting Diodes Requiring a Lower Driving Voltage, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp301650x, 116, 15, 8699-8706, 2012.04, Novel starburst type amorphous materials N-1,N-1,N-4,N-1-tetra(biphenyl-4-yl)benzene-1,4-diamine, N-1,N-1,N-1,N-1-tetrakis (4-(thio-phen-2-yl)phenyl)benzene-1,4-diamine, and N-1,N-1,N-1,N-1-tetrakis(4-(benzo[b]thiophen-2-yl)phenyl)benzene-1,4-diamine are synthesized and applied as hole injection layers (HILs) in organic light-emitting diodes (OLEDs). OLEDs containing these materials as a HIL demonstrated a significant reduction in the required driving voltage. We found that these molecules form a horizontally oriented amorphous thin film upon vacuum deposition. We observed a close correlation between the reduction of driving voltage in OLEDs and the orientation parameter of the organic thin films. We identified that the enhanced horizontal molecular orientation results in the lower driving voltage because of a decrease in the hole injection barrier at the anode/HIL interface.. |
| 782. | Kenichi Goushi, Kou Yoshida, Keigo Sato, Chihaya Adachi, Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion, NATURE PHOTONICS, 10.1038/nphoton.2012.31, 6, 4, 253-258, 2012.04, Light emission from organic light-emitting diodes that make use of fluorescent materials have an internal quantum efficiency that is typically limited to no more than 25% due to the creation of non-radiative triplet excited states. Here, we report the use of electron-donating and electron-accepting molecules that allow a very high reverse intersystem crossing of 86.5% between non-radiative triplet and radiative singlet excited states and thus a means of achieving enhanced electroluminescence. Organic light-emitting diodes made using m-MTDATA as the donor material and 3TPYMB as the acceptor material demonstrate that external quantum efficiencies as high as 5.4% can be achieved, and we believe that the approach will offer even higher values in the future as a result of careful material selection.. |
| 783. | Korefumi Kubota, Shuzo Hirata, Yuki Shibano, Osamu Hirata, Masayuki Yahiro, Chihaya Adachi, Liquid Carbazole Substituted with a Poly(ethylene oxide) Group and Its Application for Liquid Organic Light-emitting Diodes, CHEMISTRY LETTERS, 10.1246/cl.2012.934, 41, 9, 934-936, 2012.09, We report efficient carrier injection characteristics in liquid organic light-emitting diodes (OLEDs). The use of a liquid carbazole substituted with a poly(ethylene oxide) (PEO) chain provided a substantial improvement in carrier injection compared to devices constructed with carbazoles without PEO units. The external electroluminescence quantum efficiency (Phi(EL).) of an OLED with the liquid carbazole as an emitting layer resulted in Phi(EL) = 0.75%, 25 times higher Phi(EL) than that of our previous liquid OLED without electrolyte.. |
| 784. | Takeshi Komino, Hiroko Nomura, Masayuki Yahiro, Chihaya Adachi, Real-Time Measurement of Molecular Orientational Randomization Dynamics during Annealing Treatments by In-Situ Ellipsometry, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/Jp302158k, 116, 21, 11584-11588, 2012.05, The molecular orientational randomization dynamics of organic thin films during annealing were measured by real-time in situ ellipsometry. The spirofluorene derivatives used in this work formed amorphous thin films with the molecules oriented parallel to the substrates when the films were vacuum deposited at room temperature. However, the molecular orientations became random when the thin films were annealed at temperatures higher than the glass transition temperature because molecular migration occurred. Analysis of the ellipsometry results using a graded model showed that the randomization of the molecular orientations depended on the thickness of the thin film. This suggests that the surface glass transition temperatures are lower than the bulk glass transition temperatures in the thin films of these small molecules.. |
| 785. | Zou Ye, Zhen Bo, William John Potscavage, Masaya Hirade, ZHENG YANQIONG, CHIHAYA ADACHI, Very high open-circuit voltage of 5.89 V in organic solar cells with 10-fold-tandem structure, APPLIED PHYSICS LETTERS, 10.1063/1.4729009, 100, 24, 243302, 2012.06. |
| 786. | Mayo Miyake, Hizuru Nakajima, Akihide Hemmi, Masayuki Yahiro, Chihaya Adachi, Nobuaki Soh, Ryoichi Ishimatsu, Koji Nakano, Katsumi Uchiyama, Toshihiko Imato, Performance of an organic photodiode as an optical defector and its application to fluorometric flow-immunoassay for IgA, TALANTA, 10.1016/j.talanta.2012.02.006, 96, 132-139, 2012.07, The performance of an organic thin film photodiode (OPD), fabricated from a hetero-junction comprised of two layers of C-60 and a phthalocyanine-Cu(II) complex was evaluated by detecting the chemiluminescence generated from the reaction of luminol with horseradish peroxidase in the presence of H2O2, and the fluorescence from resorufin, as an optical detector. The photocurrent of the OPD was linear with respect to the power of light from a commercial LED. The sensitivity of the OPD was sufficient for detecting chemiluminescence with a power 0.1 mu W/cm(2). The OPD was successfully used in a flow-immunoassay for IgA, a marker of human stress, in which a sandwich immunoassay was carried out on the microchip and the fluorescence from resorufin, produced by the enzymatic reaction, was detected. The detection limits for resorufin and IgA were 5.0 mu M and 16 ng/mL, respectively. The photosensitivity of the OPD remained relatively constant for a minimum of one year. (C) 2012 Elsevier B.V. All rights reserved.. |
| 787. | Ryosuke Kondo, Takuma Yasuda, YANG YUSEOK, Jun Yun Kim, CHIHAYA ADACHI, Highly luminescent π-conjugated dithienometalloles: photophysical properties and their application in organic light-emitting diodes, J. Mater. Chem, 10.1039/C2JM33526C, 33, 22, 16810-16816, 2012.07. |
| 788. | Kenichi Goushi, Chihaya Adachi, Efficient organic light-emitting diodes through up-conversion from triplet to singlet excited states of exciplexes, APPLIED PHYSICS LETTERS, 10.1063/1.4737006, 101, 2, 2012.07, Enhanced electroluminescence efficiency is achieved in organic light-emitting diodes through delayed fluorescence of the exciplex state formed between 4,40,4 ''-tris[3-methylphenyl(phenyl) amino]triphenylamine (m-MTDATA) as an electron-donating material and 2,8-bis(diphenylphosphoryl) dibenzo[b,d]thiophene (PPT) as an electron-accepting material. The devices exhibited maximum external electroluminescence quantum and power efficiencies of 10.0% and 47.0 lm/W, respectively. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737006]. |
| 789. | Kazunori Togashi, Shinataro Nomura, Norimasa Yokoyama, Takuma Yasuda, CHIHAYA ADACHI, Low Driving Voltage Characteristics of Triphenylene Derivatives as Electron Transport Materials in Organic Light-Emitting Diodes, J. Mater. Chem. 2012, 22, 20689-20695., 10.1039/c2jm33669c, 22, 38, 20689-20695, 2012.08. |
| 790. | Sae Youn Lee, Takuma Yasuda, Hiroko Nomura, Chihaya Adachi, High-efficiency organic light-emitting diodes utilizing thermally activated delayed fluorescence from triazine-based donor-acceptor hybrid molecules, APPLIED PHYSICS LETTERS, 10.1063/1.4749285, 101, 9, 2012.08, We have designed and synthesized a high-efficiency purely organic luminescent material, 2,4-bis{3-(9H-carbazol-9-yl)-9H-carbazol-9-yl}-6-phenyl-1,3,5-triazine (CC2TA) comprising the bicarbazole donor and phenyltriazine acceptor units, which is capable of emitting thermally activated delayed fluorescence. The molecular design of CC2TA allows spatial separation of HOMO and LUMO on the donor and acceptor fragments, respectively, leading to an exceptionally small singlet-triplet exchange energy (Delta E-ST = 0.06 eV) together with a high triplet energy. Furthermore, a high external electroluminescence quantum efficiency as high as 11% +/- 1% has been achieved in the sky-blue organic light-emitting diodes employing CC2TA as an emitter. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4749285]. |
| 791. | Qisheng Zhang, Jie Li, Katsuyuki Shizu, Shuping Huang, Shuzo Hirata, Hiroshi Miyazaki, Chihaya Adachi, Design of Efficient Thermally Activated Delayed Fluorescence Materials for Pure Blue Organic Light Emitting Diodes, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja306538w, 134, 36, 14706-14709, 2012.09, Efficient thermally activated delayed fluorescence (TADF) has been characterized for a carbazole/sulfone derivative in both solutions and doped films. A pure blue organic light emitting diode (OLED) based on this compound demonstrates a very high external quantum efficiency (EQE) of nearly 10% at low current density. Because TADF only occurs in a bipolar system where donor and acceptor centered (3)pi pi* states are close to or higher than the triplet intramolecular charge transfer (3CT) state, control of the pi-conjugation length of both donor and acceptor is considered to be as important as breaking the pi-conjugation between them in blue TADF material design.. |
| 792. | Chang-Hoon Shim, Shuzo Hirata, Juro Oshima, Tomohiko Edura, Reiji Hattori, Chihaya Adachi, Uniform and refreshable liquid electroluminescent device with a back side reservoir, APPLIED PHYSICS LETTERS, 10.1063/1.4749791, 101, 11, 2012.09, We fabricated a refreshable organic light-emitting diode with a liquid emitting layer. This device has a mesh-structured cathode and a liquid reservoir in the back side of the cathode for easy convection of the liquid emitter. The small uniform gap between the electrodes was fabricated by means of micro-electro-mechanical systems (MEMS) processing. Although the device luminance decreased because of decomposition of the liquid emitters under the drive current, the decreased emission was quickly recovered to the initial state by convectional replacement of the decomposed emitters with fresh emitters through the holes of the mesh cathode. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4749791]. |
| 793. | Yukitami Mizuno, Isao Takasu, Shuichi Uchikoga, Shintaro Enomoto, Tomoaki Sawabe, Akio Amano, Atsushi Wada, Tomoko Sugizaki, Jiro Yoshida, Tomio Ono, Chihaya Adachi, Fluorinated Carbazole Derivatives as Wide-Energy-Gap Host Material for Blue Phosphorescent Organic Light-Emitting Diodes, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp303085h, 116, 39, 20681-20687, 2012.10, 2,7-Difluo-carbazole and 2,4,5,7-tetrafluoro-carbazole were synthesized as new building blocks of wide-energy-gap host material for phosphorescent organic light-emitting diodes (PHOLEDs). These fluorinated positions in the carbazole ring were determined on the basis of density functional theory g calculation results. Spectroscopic analyses supported the hypothesis that poly(N-vinyl-2,7-difluoro-carbazole) (2,7-F-PVK) with the fluorinated pendant group possessed a wide energy gap, leading to the exciton energy confinement on the blue phosphorescent dopant as well as nonsubstituted poly(N-vinyl-carbazole) (PVK). 2,7-F-PVK was used in solution-processed blue PHOLED to achieve 27 cd/A at 760 cd/m(2), which is 1.8 times higher than that of nonsubstituted PVK We assumed that the replacement of nonsubstituted PVK with 2,7-F-PVK improved the charge balance in the emission layer, while keeping the exciton confinement effect. The fluorination of the carbazole ring is a useful molecular design strategy for wide-energy-gap host material.. |
| 794. | Yukitani Mizuno, Isao Takasu, Shuichi Uchikoga, Shuichi Enomoto, Tomoaki Sawabe, Akiko Amano, Atsushi Wada, Tomoko Sugizaki, Jiro Yoshida, Tomio Ono, CHIHAYA ADACHI, Fluorinated Carbazole Derivatives as Wide-Energy-Gap Host Material for Blue Phosphorescent Organic Light-Emitting Diodes, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp303085h, 116, 39, 20681-20687, 2012.10. |
| 795. | YANG YUSEOK, Takuma Yasuda, CHIHAYA ADACHI, Organic Single-Crystal Transistors Based on pi-Extended Heteroheptacene Microribbons, Bull. Chem. Soc. Jpn. 2012, 85, 1186-1191., 10.1246/bcsj.20120178, 85, 1186-1191, 2012.10. |
| 796. | Hiroyuki Tanaka, Katsuyuki Shizu, Hiroshi Miyazaki, CHIHAYA ADACHI, Efficient green thermally activated delayed fluorescence (TADF) from a phenoxazine-triphenyltriazine (PXZ-TRZ) derivative, Chem. Comm., 10.1039/C2CC36237F, 48, 93, 11392-11394, 2012.11. |
| 797. | Gabor Mehes, Hiroko Nomura, Tetsuya Nakagawa, CHIHAYA ADACHI, Enhanced Electroluminescence Efficiency in a Spiro-Acridine Derivative through Thermally Activated Delayed Fluorescence, Angewandte Chemie, 10.1002/anie.201206289, 51, 45, 11311-11315, 2012.11. |
| 798. | Manabu Nakata, Kenji Kawano, Mao Yasumatsu, Masayuki Yahiro, Chihaya Adachi, Formation of nanostructured donor/acceptor interfaces and their application to organic photovoltaic cells, THIN SOLID FILMS, 10.1016/j.tsf.2012.08.008, 522, 357-360, 2012.11, Organic nanostructures can enhance the device performance of organic photovoltaic (OPV) cells, because a significantly large area of a donor/acceptor heterointerface can be prepared. In this study, we improved the performance of OPV cells composed of cupper phthalocyanine (CuPc)/fullerene (C-60) by introducing a pentacene nanometer-sized grain layer into an anode/CuPc layer. The smallest featured grain sizes are as small as 100 nm, resulting in the formation of ragged heterojunctions. We show that power conversion efficiency is enhanced up to 20% compared with that of conventional planar heterojunctions. (C) 2012 Elsevier B.V. All rights reserved.. |
| 799. | Hiroki Uoyama, Kenichi Goushi, Katsuyuki Shizu, Hiroko Nomura, Chihaya Adachi, Highly efficient organic light-emitting diodes from delayed fluorescence, NATURE, 10.1038/nature11687, 492, 7428, 234-+, 2012.12, The inherent flexibility afforded by molecular design has accelerated the development of a wide variety of organic semiconductors over the past two decades. In particular, great advances have been made in the development of materials for organic light-emitting diodes (OLEDs), from early devices based on fluorescent molecules(1) to those using phosphorescent molecules(2,3). In OLEDs, electrically injected charge carriers recombine to form singlet and triplet excitons in a 1:3 ratio(1); the use of phosphorescent metal-organic complexes exploits the normally non-radiative triplet excitons and so enhances the overall electroluminescence efficiency(2,3). Here we report a class of metal-free organic electroluminescent molecules in which the energy gap between the singlet and triplet excited states is minimized by design(4), thereby promoting highly efficient spin up-conversion from non-radiative triplet states to radiative singlet states while maintaining high radiative decay rates, of more than 10(6) decays per second. In other words, these molecules harness both singlet and triplet excitons for light emission through fluorescence decay channels, leading to an intrinsic fluorescence efficiency in excess of 90 per cent and a very high external electroluminescence efficiency, of more than 19 per cent, which is comparable to that achieved in high-efficiency phosphorescence-based OLEDs(3).. |
| 800. | Takashi Kasahara, Shigeyuki Matsunami, Tomohiko Edura, Juro Oshima, Chihaya Adachi, Shuichi Shoji, Jun Mizuno, Fabrication and performance evaluation of microfluidic organic light emitting diode, SENSORS AND ACTUATORS A-PHYSICAL, 10.1016/j.sna.2012.12.031, 195, 219-223, 2013.06, In this study, we fabricated a microfluidic organic light emitting diode (OLED) and evaluated its performance. The microchip consisted of a 3 x 3 matrix array of OLED pixels in SU-8 microchannels sandwiched by indium tin oxide (ITO) anode and cathode pairs. Liquid organic semiconductors introduced into the microchannels were employed as the light emitters. Electroluminescence was successfully observed at the emitting area of the microchannels. A current density of 0.298 mA/cm(2) was measured at 70V. In our prototype microfluidic OLED, the patterning of the liquid emitters was confirmed in the microchannels on a single chip. This result shows that the proposed structure can be applicable for liquid-based display. (C) 2013 Elsevier B.V. All rights reserved.. |
| 801. | Atsushi Wada, Takuma Yasuda, Qisheng Zhang, Yu Seok Yang, Isao Takasu, Shintaro Enomoto, Chihaya Adachi, A host material consisting of a phosphinic amide directly linked donor-acceptor structure for efficient blue phosphorescent organic light-emitting diodes, Journal of Materials Chemistry C, 10.1039/c3tc00939d, 1, 13, 2404-2407, 2013.04, A host material with a high triplet excited-state energy level and a deep HOMO energy level has been developed by directly linking the donor and acceptor units through a phosphinic amide. Phosphorescent organic light-emitting diodes containing this material and a deep-blue dopant achieved an external quantum efficiency of 19.7%. © The Royal Society of Chemistry 2013.. |
| 802. | Shuzo Hirata, Kenro Totani, Junxiang Zhang, Takashi Yamashita, Hironori Kaji, Seth R. Marder, Toshiyuki Watanabe, Chihaya Adachi, Efficient Persistent Room Temperature Phosphorescence in Organic Amorphous Materials under Ambient Conditions, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.201203706, 23, 27, 3386-3397, 2013.07, Persistent emission with a long lifetime (>1 s) from organic materials can only be observed at a low temperature, because of the significant nonradiative deactivation pathway that occurs at room-temperature (RT). If organic materials with persistent RT emission in air could be developed, they could potentially be utilized for a variety of applications. Here, organic host-guest materials with efficient persistent RT phosphorescence (RTP) are developed by minimizing the nonradiative deactivation pathway of triplet excitons. The nonradiative deactivation pathway is dependent on both nonradiative deactivation of the guest and quenching by diffusional motion of the host. The rigidity and oxygen barrier properties of the steroidal compound used as the host suppressed the quenching, and the aromatic hydrocarbon used as the guest is highly deuterated to minimize nonradiative deactivation of the guest. Red-green-blue persistent RTP with a lifetime >1 s and a quantum yield >10% in air is realized for a pure organic material.. |
| 803. | Masaya Hirade, Takuma Yasuda, CHIHAYA ADACHI, Effects of Intramolecular Donor-Acceptor Interactions on Bimolecular Recombination in Small-Molecule Organic Photovoltaic Cells, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp400386q, 117, 10, 4986-4991, 2013.03. |
| 804. | Masaya Hirade, Takuma Yasuda, Chihaya Adachi, Effects of Intramolecular Donor-Acceptor Interactions on Bimolecular Recombination in Small-Molecule Organic Photovoltaic Cells, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp400386q, 117, 10, 4986-4991, 2013.03, To enhance the device performance of bulk heterojunction organic photovoltaic (OPV) cells, recombination processes must be suppressed. Here, we prepared OPV cells using donor materials composed of different electron-rich donor and electron-deficient acceptor units and the acceptor material 6,6-phenyl-C61-butyric acid methyl ester. The effects of the polarization of the donor materials which was induced by the intramolecular donor-acceptor (D-A) interactions on the bimolecular recombination constant of each device were studied using a time-of-flight method. A large D-A interaction decreased the bimolecular recombination constant, increasing the fill factor of the device. An active layer with a large dielectric constant led to a small Coulomb capture radius between the radical cations and anions. Overall, a larger D-A interaction enhanced the device performance of small-molecule OPV cells.. |
| 805. | Takeshi Komino, Hiroko Nomura, Masayuki Yahiro, Chihaya Adachi, Reorganization of the molecular orientation at the organic/substrate interface in spirofluorene thin films, CHEMICAL PHYSICS LETTERS, 10.1016/j.cplett.2013.01.056, 563, 70-75, 2013.03, The thermal annealing treatment of an organic non-crystalline film of spirofluorene causes the randomization of the molecular orientation through molecular migration. However, the magnitude of the randomization depends on the depth in the film. The comparison of variable-angle spectroscopic ellipsometry, thermally stimulated current, and field-effect transistor characteristics measurements revealed that the molecular orientation in the bulk was randomized by annealing but was still partially maintained at the organic/substrate interface. This difference in condensed states between the interface and the bulk originates from a difference in glass transition temperature. (C) 2013 Elsevier B. V. All rights reserved.. |
| 806. | Kazunori Togashi, Takuma Yasuda, Chihaya Adachi, Triphenylene-based Host Materials for Low-voltage, Highly Efficient Red Phosphorescent Organic Light-emitting Diodes, CHEMISTRY LETTERS, 10.1246/cl.121247, 42, 4, 383-385, 2013.04, Triphenylene-based host materials BDBF-TP and BDBT-TP were synthesized for use in red phosphorescent organic light-emitting diodes (PHOLEDs). The current-voltage characteristics of hole- and electron-only devices revealed that BDBT-TP exhibits better bipolar carrier transport properties than 4,4'-bis(carbazol-9-yl)-1,1'-biphenyl and BDBF-TP. Red PHOLEDs containing BDBF-TP or BDBT-TP as the host showed a lower driving voltage, higher external quantum efficiency, and lower efficiency roll-off at high current density.. |
| 807. | Jun Yun Kim, Takuma Yasuda, Yu Seok Yang, Chihaya Adachi, Bifunctional star-burst amorphous molecular materials for OLEDs: Achieving highly efficient solid-state luminescence and carrier transport induced by spontaneous molecular orientation, Advanced Materials, 10.1002/adma.201204902, 25, 19, 2666-2671, 2013.05, Bifunctional star-burst amorphous molecular materials displaying both efficient solid-state luminescence and high hole-transport properties are developed in this study. A high external electroluminescence quantum efficiency up to 5.9% is attained in OLEDs employing the developed amorphous materials. It is revealed that the spontaneous horizontal orientation of these light-emitting molecules in their molecular-condensed states leads to a remarkable enhancement of the electroluminescence efficiencies and carrier-transport properties. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.. |
| 808. | Munetomo Inoue, Kenichi Goushi, Kuniaki Endo, Hiroko Nomura, CHIHAYA ADACHI, Reduced amplified spontaneous emission threshold in organic semiconductor laser structure with relaxed roll-off characteristics under high current densities, Journal of Luminescence, 10.1016/j.jlumin.2013.04.001, 2013.04. |
| 809. | Yan-qiong Zheng, William J. Potscavage, Takeshi Komino, Chihaya Adachi, Highly efficient bulk heterojunction photovoltaic cell based on tris[4-(5-phenylthiophen-2-yl)phenyl]amine and C-70 combined with optimized electron transport layer, APPLIED PHYSICS LETTERS, 10.1063/1.4801954, 102, 15, 2013.04, Efficient bulk heterojunction (BHJ) photovoltaic cells (PVs) based on 5 wt.% donors and C-70 were fabricated. Tris[4-(5-phenylthiophen-2-yl)phenyl]-amine (TPTPA)-based BHJ PVs show higher power conversion efficiency (eta(PCE)) than aluminum phthalocyanine chloride-based BHJ PVs. Although the absorption of AlPcCl is complementary to that of C-70, TPTPA's high hole mobility and symmetrical molecular structure are likely to be crucial contributing factors to the higher eta(PCE). Phase separation occurs in the 5%-TPTPA blend. The device was optimized via replacement of the bathocuproine buffer by a combination of 3,4,9,10-perylenetetracarboxylic bis-benzimidazole and bathocuproine. eta(PCE) of 5.96% is achieved because of the decreased series resistance. (C) 2013 AIP Publishing LLC [http://dx.doi.org/10.1063/1.4801954]. |
| 810. | Yan-Qiong Zheng, William J. Potscavage, Takeshi Komino, Masaya Hirade, Junji Adachi, Chihaya Adachi, Highly efficient bulk heterojunction photovoltaic cells based on C 70 and tetraphenyldibenzoperiflanthene, Applied Physics Letters, 10.1063/1.4801647, 102, 14, 2013.04, Highly efficient photovoltaic cells based on a bulk heterojunction configuration composed of C70 with various donor materials at 5 wt.% donor concentration were fabricated. The tetraphenyldibenzoperiflanthene (DBP) donor achieved the highest power conversion efficiency (ηPCE) of 6.4% for the optimized cell. The improved performance with DBP arises from a combination of a higher absorption coefficient than 1,1-bis-(4-bis(4-methyl- phenyl)-amino-phenyl)-cyclohexane and a symmetrical molecular structure. The high ηPCE with only 5 wt. donor is attributed to a sufficient donor concentration for enhanced Frenkel exciton dissociation in C70, while efficiency and electron mobility decrease at higher donor concentrations. © 2013 AIP Publishing LLC.. |
| 811. | Kazunori Togashi, Yuta Sagara, Takuma Yasuda, CHIHAYA ADACHI, Molecular Design of High Molecular Orientation Electron Transport Materials and Application to Organic Light-Emitting Diodes, Chem. Lett. 3013, 42, in press., 2013.04. |
| 812. | Maki Taguchi, Tetsuya Nakagawa, Takuya Nakashima, CHIHAYA ADACHI, Photo-patternable electroluminescence based on one-way photoisomerization reaction of tetraoxidized triangle terarylenes, Chem. Comm., 10.1039/C3CC41825A, 2013.05. |
| 813. | Jie Li, Tetsuya Nakagawa, James MacDonald, Qisheng Zhang, Hiroko Nomura, Hiroshi Miyazaki, Chihaya Adachi, Highly Efficient Organic Light-Emitting Diode Based on a Hidden Thermally Activated Delayed Fluorescence Channel in a Heptazine Derivative, ADVANCED MATERIALS, 10.1002/adma.201300575, 25, 24, 3319-3323, 2013.06. |
| 814. | Keigo Sato, Katsuyuki Shizu, Kazuaki Yoshimura, Atsushi Kawada, Hiroshi Miyazaki, Chihaya Adachi, Organic luminescent molecule with energetically equivalent singlet and triplet excited states for organic light-emitting diodes, Physical Review Letters, 10.1103/PhysRevLett.110.247401, 110, 24, 247401, 2013.06, We demonstrate an organic molecule with an energy gap between its singlet and triplet excited states of almost zero (ΔEST∼0 eV). Such separation was realized through proper combination of an electron-donating indolocarbazole group and a diphenyltriazine electron-accepting moiety. Calculated and measured ΔEST were 0.003 and 0.02 eV, respectively. A total photoluminescence efficiency of 59%±2% with 45%±2% from a delayed component and 14%±2% from a prompt component was obtained for a doped film. Organic light emitting diodes containing this molecule as an emitting dopant exhibited an unexpectedly high external electroluminescence efficiency of ηEQE=14%±1%. © 2013 American Physical Society.. |
| 815. | Yu Seok Yang, Takuma Yasuda, Hayato Kakizoe, Hiroyuki Mieno, Hiori Kino, Yoshitaka Tateyama, Chihaya Adachi, High performance organic field-effect transistors based on single-crystal microribbons and microsheets of solution-processed dithieno[3,2-b:2′, 3′-d]thiophene derivatives, Chemical Communications, 10.1039/c3cc42114g, 49, 58, 6483-6485, 2013.07, We present π-conjugated dithieno[3,2-b:2′,3′-d]thiophene derivatives that act as high-performance p-type organic semiconductors. These molecules self-organize into single-crystal microribbons or microsheets. High carrier mobilities of up to 10.2 cm< sup> 2< /sup> V< sup> -1< /sup> s< sup> -1< /sup> and high on/off ratios of ∼10< sup> 7< /sup> have been achieved in organic single-crystal field-effect transistors. © 2013 The Royal Society of Chemistry.. |
| 816. | Woong Shin, Takuma Yasuda, Go Watanabe, Yu Seok Yang, Chihaya Adachi, Self-Organizing Mesomorphic Diketopyrrolopyrrole Derivatives for Efficient Solution-Processed Organic Solar Cells, CHEMISTRY OF MATERIALS, 10.1021/cm401244x, 25, 12, 2549-2556, 2549-2556, 2013.06, We describe the synthesis, self-organization, and photovoltaic properties of diketopyrrolopyrrole (DPP)-based mesomorphic small-molecule materials, 3,6-bis{5-(4-alkylphenyl)thiophen-2-yl}-2,5-di(2-ethylhexyl)-pyrrolo[3,4-c]-pyrrole-1,4-diones (DPP-TP6 and DPP-TP12), which have strong visible absorption characteristics. The effects of varying terminal alkyl chains on the self-assembling properties and photovoltaic device performances have been studied. With the appropriate ratio of the lengths of the alkyl chains to its rigid DPP core, DPP-TP6 exhibits liquid-crystalline properties and forms well-developed nanostructured bulk heterojunction (BHJ) architectures with a fullerene derivative (PC71BM). Organic solar cells (OSCs) employing BHJ DPP-TP6:PC71BM films show a power conversion efficiency as high as 4.3% with a high open-circuit voltage of 0.93 V and a fill factor of 0.55. These results demonstrate that liquid-crystalline organization to direct molecular self-assembly is a promising strategy for fabricating high-performance solution-processed small-molecule OSCs.. |
| 817. | CHIHAYA ADACHI, Oxadiazole- and Triazole-Based Highly-Efficient Thermally-Activated Delayed Fluorescence Emitters for Organic Light-Emitting Diodes, J. Mater. Chem. C 2013, 1, 4599-4604., 2013.06. |
| 818. | Takeshi Komino, Hirokazu Kuwabara, Masaaki Ikeda, Masayuki Yahiro, Kazuo Takimiya, Chihaya Adachi, Droplet Manipulation by an External Electric Field for Crystalline Film Growth, LANGMUIR, 10.1021/la401729k, 29, 30, 9592-9597, 9592-9597, 2013.07, Combining droplet manipulation by the application of an electric field with inkjet printing is proposed as a unique technique to control the surface wettability of substrates for solution-processed organic field-effect transistors (FETs). With the use of this technique, uniform thin films of 2,7-dioctyl[1]benzothieno[2,3,-b][1]benzothiopene (C-8-technique, uniform thin films of 2,7-dioctyl[1]benzothieno[2,3,-b][1]benzothiopene (C-8-BTBT) could be fabricated on the channels of FET substrates without self-assembled monolayer treatment. High-speed camera observation revealed that the crystals formed at the solid/liquid interface. The coverage of the crystals on the channels depended on the ac frequency of the external electric field applied during film formation, leading to a wide variation in the carrier transport of the films. The highest hole mobility of 0.03 cm(2) V-1 s(-1) was obtained when the coverage was maximized with an ac frequency of 1 kHz.. |
| 819. | CHIHAYA ADACHI, Promising operational stability of high-efficiency organic light-emitting diodes based on thermally activated delayed fluorescence, SCIENTIFIC REPORTS, 10.1038/srep02127, 3, 2013.07. |
| 820. | Ryoichi Ishimatsu, Shigeyuki Matsunami, Katsuyuki Shizu, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Solvent Effect on Thermally Activated Delayed Fluorescence by 1,2,3,5-Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene, JOURNAL OF PHYSICAL CHEMISTRY A, 10.1021/jp404120s, 117, 27, 5607-5612, 5607-5612, 2013.07, Thermally activated delayed fluorescence (TADF) is fluorescence arising from a reverse intersystem crossing (RISC) from the lowest triplet (T-1) to the singlet excited state (S-1), where these states are separated by a small energy gap (Delta E-st), followed by a radiative transition to the ground state (S-0). Rate constants relating TADF processes in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) were determined at four different solvent polarities (toluene, dichloromethane, ethanol, and acetonitrile). We revealed that the rate constant of RISC, k(RISC), which is the most important factor for TADF, was significantly enhanced by a reduced Delta E-st, in more polar solvents. The smaller Delta E-st was mainly attributable to a stabilization of the S-1 state. This stabilization also induced a Stokes shift in fluorescence through a relatively large change of the dipole moment between S-1 and S-0 states (17 D). Despite of this factor, we observed a negative correlation between Delta E-st and efficiency of the delayed fluorescence (phi(d)). This was ascribed to a lower intersystem crossing rate, k(ISC), and increase nonradiative decay from S-1, k(nt)(s), in polar solvents.. |
| 821. | Le Zhang, Hajime Nakanotani, Chihaya Adachi, Capacitance-voltage characteristics of a 4,4 '-bis[(N-carbazole)styryl]biphenyl based organic light-emitting diode: Implications for characteristic times and their distribution, APPLIED PHYSICS LETTERS, 10.1063/1.4819436, 103, 9, 2013.08, The characteristic times and their distributions of a fluorescent 4,4'-bis[(N-carbazole)styryl]biphenyl-based organic light-emitting diode (OLED) were studied using impedance spectroscopy. The four defined characteristic times (transit time, recombination time, trapping time, and ac characteristic time) and their dc bias dependences were obtained from the frequency dependence of capacitance. The trapped carrier density distribution in the time domain was revealed from the voltage dependence of the OLED. The relative value of each characteristic time is suggested to play an important role in determining the profile of the frequency-and voltage-dependent capacitance of OLEDs. (C) 2013 AIP Publishing LLC.. |
| 822. | Takeshi Komino, Hiroko Nomura, Takahiro Koyanagi, Chihaya Adachi, Suppression of Efficiency Roll-Off Characteristics in Thermally Activated Delayed Fluorescence Based Organic Light-Emitting Diodes Using Randomly Oriented Host Molecules, CHEMISTRY OF MATERIALS, 10.1021/cm4011597, 25, 15, 3038-3047, 3038-3047, 2013.08, The efficiency roll-off characteristics in highly efficient thermally activated delayed fluorescence (TADF) based organic light-emitting diodes (OLEDs) were effectively suppressed by controlling the molecular orientation of a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) host matrix. The hole mobility in the light 2 emitting layer was found to govern the magnitude of this suppression. Three-dimensional finite-difference time-domain calculations and photoluminescence quantum yield measurements revealed that the optical characteristics of the fabricated devices and photophysical properties of the TADF emitter did not affect efficiency roll-off CBP molecules adopted random orientations when films were fabricated at high temperature (350 K), resulting in low hole mobility, and shifting the recombination zone away from the interface of the emitting layer with the electron transporting layer. When CBP was randomly orientated, efficiency roll-off was suppressed by 30% at a current density of 100 mA cm(-2). This result indicates that control of the molecular orientation of the host can allow us to indirectly tune the carrier balance in OLEDs.. |
| 823. | Hiroyuki Tanaka, Katsuyuki Shizu, Hajime Nakanotani, Chihaya Adachi, Twisted Intramolecular Charge Transfer State for Long-Wavelength Thermally Activated Delayed Fluorescence, CHEMISTRY OF MATERIALS, 10.1021/cm402428a, 25, 18, 3766-3771, 3766-3771, 2013.09, Emission wavelength tuning of thermally activated delayed fluorescence from green to orange in solid state films is demonstrated. Emission tuning occurs by stabilization of the intramolecular charge transfer state between a phenoxazine (PXZ) donor unit and 2,4,6-triphenyl-1,3,5-triazine (TRZ) acceptor unit separated by a large twist angle. The emission wavelengths of mono-, bis-, and tri-PXZ-substituted TRZ exhibit a gradual red shift while maintaining a small energy gap between the singlet and triplet excited states. An organic light-emitting diode containing a tri-PXZ-TRZ emitter exhibited a maximum external quantum efficiency of 13.3 +/- 0.5% with yellow-orange emission.. |
| 824. | Shuping Huang, Qisheng Zhang, Yoshihito Shiota, Tetsuya Nakagawa, Kazuhiro Kuwabara, Kazunari Yoshizawa, Chihaya Adachi, Computational prediction for singlet- and triplet-transition energies of charge-transfer compounds, Journal of Chemical Theory and Computation, 10.1021/ct400415r, 9, 9, 3872-3877, 3872-3877, 2013.09, Our work reveals a high dependence on charge-transfer (CT) amounts for the optimal Hartree-Fock percentage in the exchange-correlation functional of time-dependent density functional theory (TD-DFT) and the error of a vertical transition energy calculated by a given functional. Using these relations, the zero-zero transition energies of the first singlet and first triplet excited states of various CT compounds are accurately reproduced. 3CT and locally excited triplet (3LE) states are well distinguished and calculated independently. © 2013 American Chemical Society.. |
| 825. | Takuro Nishimoto, Takuma Yasuda, Sae Youn Lee, Ryosuke Kondo, Chihaya Adachi, A six-carbazole-decorated cyclophosphazene as a host with high triplet energy to realize efficient delayed-fluorescence OLEDs, MATERIALS HORIZONS, 10.1039/c3mh00079f, 1, 2, 264-269, 2014.03, A high triplet energy (ET) host material, hexakis(9H-carbazol-9-yl) cyclotriphosphazene (PzCz), is used in high-efficiency organic light-emitting diodes (OLEDs). PzCz (E-T = 3.00 eV) functions as an effective host for thermally activated delayed fluorescence (TADF) molecules. Highest external electroluminescence quantum efficiencies over 15% and 18% are achieved for blue-green and green TADF-OLEDs, respectively.. |
| 826. | Yasushi Koishikawa, Hiroshi Miyazaki, Masayuki Yahiro, Chihaya Adachi, Multi-layered organic light-emitting diode fabrication using low molecular weight materials by electrospray method, Thin Solid Films, 10.1016/j.tsf.2013.07.083, 545, 527-532, 527-532, 2013.10, Active technology development efforts to improve the productivity of organic light emitting diode (OLED) fabrication using wet processes based on ink-jet technology have been conducted by taking advantage of the low cost and large area processability of organic materials.However, OLEDs formed by conventional wet processes have been unable to reproduce the high performance levels of OLEDs that were mass-produced by dry processes based on vacuum deposition.We have therefore focused on the electrospray (ES) method as a potential fabrication technology.In this paper, we report on a multilayer thin-film fabrication process with low molecular-weight materials using an ES method that allows atomization of the organic materials by Coulomb repulsion and successive adhesion of solid-state multi-layered thin films.We demonstrate OLED fabrication by this ES method and the characteristics of the resulting devices.© 2013 Elsevier B.V.All rights reserved.. |
| 827. | Yoshiyuki Nonoguchi, Kenji Ohashi, Rui Kanazawa, Koji Ashiba, Kenji Hata, Tetsuya Nakagawa, Chihaya Adachi, Tomoaki Tanase, Tsuyoshi Kawai, Systematic Conversion of Single Walled Carbon Nanotubes into n-type Thermoelectric Materials by Molecular Dopants, SCIENTIFIC REPORTS, 10.1038/srep03344(2013), 3, 2013.11, Thermoelectrics is a challenging issue for modern and future energy conversion and recovery technology. Carbon nanotubes are promising active thermoelectic materials owing to their narrow bandgap energy and high charge carrier mobility, and they can be integrated into flexible thermoelectrics that can recover any waste heat. We here report air-stable n-type single walled carbon nanotubes with a variety of weak electron donors in the range of HOMO level between ca. -4.4 eV and ca. -5.6 eV, in which partial uphill electron injection from the dopant to the conduction band of single walled carbon nanotubes is dominant. We display flexible films of the doped single walled carbon nanotubes possessing significantly large thermoelectric effect, which is applicable to flexible ambient thermoelectric. |
| 828. | CHIHAYA ADACHI, Plasma-tolerant structure for organic light-emitting diodes with aluminum cathodes fabricated by DC magnetron sputtering: Using a Li-doped electron transport layer, ORGANIC ELECTRONICS, 10.1016/j.orgel.2013.08.020, 14, 11, 2994-2999, 2013.11. |
| 829. | CHIHAYA ADACHI, Multi-color light-emitting transistors composed of organic single crystals, ORGANIC ELECTRONICS, 10.1016/j.orgel.2013.07.025, 14, 11, 2737-2742, 2013.11. |
| 830. | Kensuke Masui, Hajime Nakanotani, Chihaya Adachi, Analysis of exciton annihilation in high-efficiency sky-blue organic light-emitting diodes with thermally activated delayed fluorescence, ORGANIC ELECTRONICS, 10.1016/j.orgel.2013.07.010, 14, 11, 2721-2726, 2721-2726, 2013.11, We study external quantum efficiency (eta(EQE)) roll-off in organic light-emitting diodes (OLEDs) using thermally-activated delayed fluorescence (TADF) of 4,5-di (9H-carbazol-9-yl) phthalonitrile (2CzPN). Using 2CzPN intramolecular rate constants from optical analyses, we construct an exciton quenching model incorporating intersystem crossing and reverse intersystem crossing. The model indicates that singlet-triplet annihilation and triplet-triplet annihilation dominate eta(EQE) roll-off because of the relatively long 2CzPN triplet lifetime of 273 mu s. This work yields a method to relax the exciton quenching process in TADF based OLEDs. (C) 2013 Elsevier B. V. All rights reserved.. |
| 831. | Ryoichi Ishimatsu, Azusa Naruse, Rong Liu, Koji Nakano, Masayuki Yahiro, Chihaya Adachi, Toshihiko Imato, An organic thin film photodiode as a portable photodetector for the detection of alkylphenol polyethoxylates by a flow fluorescence-immunoassay on magnetic microbeads in a microchannel, TALANTA, 10.1016/j.talanta.2013.08.044, 117, 139-145, 139-145, 2013.12, An organic thin film photodiode (OPD) was successfully employed as a portable photodetector in a competitive enzyme-linked immunosorbent assay (ELISA) of a class of nonionic surfactants, namely alkylphenol polyethoxylates (APnEOs) which are an environmental pollutant. Microbeads that were chemically immobilized with an anti-APnEOs antibody were used in the assay. The OPD consisted of a layer of copper phthalocyanine (CuPc), C-60 and a second layer of bathocuproine (BCP) with a bulk heterojunction composed of CuPc and Ca-60 prepared by a vapor deposition method on an indium-tin oxide coated glass substrate. The OPD showed an incident photon-current efficiency (IPCE) of approximately 19% for light at a wavelength of 585 nm. This relatively high IPCE at 585 nm makes it suitable for detecting the fluorescence of resorufin (lambda(em)=585 nm), the product of the competitive ELISA, produced through the enzymatic reaction of Amplex Red with horseradish peroxidase (HRP) and H2O2. A fluorometric detector was assembled on a microchip by combining the fabricated OPD and a commercial LED as a photodetector and a light source, respectively. The photocurrent of the OPD due to the fluorescence of resorufin was proportional to the concentration of resorufin in the concentration range from 0 to 8 mu M. When the fabricated OPD was used as a portable photodetector, the competitive ELISA of APnEOs using HRP labeled APnEOs (HRP-APnEOs) was performed on magnetic microbeads on which surface an anti-APnEOs antibody had been immobilized. A typical sigmoidal calibration curve was obtained and the data were in good agreement with a numerical simulation, where the photocurrent of the OPD was plotted against the concentration of APnEOs, determined via the competitive ELISA. The detection limit of the immunoassay for APnEOs was approximately 2 and 4 ppb in batch and flow system, respectively. (C) 2013 Elsevier B.V. All rights reserved.. |
| 832. | Tsuyoshi Akiyama, Tomoki Yamamoto, Takeo Oku, Masayuki Yahiro, Takashi Kurihara, Chihaya Adachi, Sunao Yamada, Mixing Effect of Gold and Silver Nanoparticles on Enhancement in Performance of Organic Thin-Film Solar Cells, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.7567/JJAP.52.122301, 52, 12, 1-122301, 2013.12, Bulk-heterojunction organic thin-film solar cells incorporating gold and silver nanoparticles were fabricated and evaluated. These nanoparticles were embedded in the hole-transport layer of the solar cells. Plasmonic absorption peaks of isolated gold and silver nanoparticles were confirmed from extinction spectra even in the hole-transport material. The incorporation of gold and silver nanoparticles increased the photoelectric conversion efficiency of organic thin-film solar cells, whose enhancement ratio was further increased by mixing gold and silver nanoparticles. (C) 2013 The Japan Society of Applied Physics. |
| 833. | Kohei Tsugita, Tomohiko Edura, Masayuki Yahiro, Chihaya Adachi, Formation of high-purity organic thin films by gas flow deposition and the effect of impurities on device characteristics, DISPLAYS, 10.1016/j.displa.2013.08.008, 34, 5, 418-422, 418-422, 2013.12, A gas flow deposition (GFD) system was developed to manufacture large-scale organic light-emitting diodes (OLEDs). A N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (alpha-NPD) thin film with a high purity of 99.97% was obtained using the GFD system. The film properties such as morphology, and electrical and optical characteristics were almost the same as those of films made by conventional vacuum thermal evaporation. (C) 2013 Elsevier B.V. All rights reserved.. |
| 834. | Jun Yun Kim; Takuma Yasuda; Yu Seok Yang; Naoki Matsumto; Chihaya Adachi, Polymorphism in 9,9-diarylfluorene-based organic semiconductors: influence on optoelectronic functions, Chem. Commun, 10.1039/C3CC48566H, 50, 1523-1526, 2013.11. |
| 835. | Daisuke Goto, Masataka Mohri, Kei Morimoto, Aleksandre Mzhavia, Chihaya Adachi, 100 m-Order Patterning of Organic Semiconductor Layers Using a Thermally Converted Precursor Technique and its Application to Organic Light Emitting Diodes, ADVANCED OPTICAL MATERIALS, 10.1002/adom.201300372, 2, 2, 110-114, 110-114, 2014.02. |
| 836. | Bo Li, Hiroko Nomura, Hiroshi Miyazaki, Qisheng Zhang, Kou Yoshida, Yoshinori Suzuma, Akihiro Orita, Junzo Otera, Chihaya Adachi, Dicarbazolyldicyanobenzenes as Thermally Activated Delayed Fluorescence Emitters: Effect of Substitution Position on Photo luminescent and Electroluminescent Properties, CHEMISTRY LETTERS, 10.1246/cl.130907, 43, 3, 319-321, 2014.03, We demonstrate two efficient blue-green thermally activated delayed fluorescence (TADF) compounds comprising a dimeric phenylcarbazole and four cyano substituents on the phenyl rings. A comparison of the 2,6-dicyano-substituted derivative (26IPNDCz) with the 3,5-dicyano-substituted derivative (35IPNDCz) shows that 26IPNDCz provides a larger dihedral angle and a lower decrease in the energy difference between the first singlet and triplet excited states (Delta E-ST) and the TADF lifetime. An organic light-emitting diode based on 26IPNDCz afforded an external quantum efficiency of 10% with reduced efficiency roll-off.. |
| 837. | Hiroyuki Mieno, Takuma Yasuda, Yu Seok Yang, Chihaya Adachi, Self-assembly, Physicochemical, and Field-effect Transistor Properties of Solution-crystallized Organic Semiconductors Based on pi-Extended Dithieno[3,2-b:2 ',3 '-d]thiophenes, CHEMISTRY LETTERS, 10.1246/cl.130914, 43, 3, 293-295, 2014.03, Thienoacene-based pi-conjugated oligomers, DTT-NP8 and DTT-BT8, were designed and synthesized. Their strong intermolecular interactions originating from S S contacts enable the fabrication of single-crystal microribbons via solution processing. Organic single-crystal transistors exhibited field-effect mobilities as high as 0.54 cm(2) s(-1) and on/off current ratio of ca. 10(6).. |
| 838. | Qisheng Zhang, Bo Li, Shuping Huang, Hiroko Nomura, Hiroyuki Tanaka, Chihaya Adachi, Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence, NATURE PHOTONICS, 10.1038/NPHOTON.2014.12, 8, 4, 326-332, 2014.04, Organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) have emerged as cheaper alternatives to high-performance phosphorescent OLEDs with noble-metal-based dopants. However, the efficiencies of blue TADF OLEDs are still low at high luminance, limiting full-colour display. Here, we report a blue OLED containing a 9,10-dihydroacridine/ diphenyl sulphone derivative that has a comparable performance to today's best phosphorescent OLEDs. The device offers an external quantum efficiency of 19.5% and reduced efficiency roll-off characteristics at high luminance. Through computational simulation, we identified six pretwisted intramolecular chargetransfer (CT) molecules with small singlet-triplet CT state splitting but different energy relationships between (CT)-C-3 and locally excited triplet ((LE)-L-3) states. Systematic comparison of their excited-state dynamics revealed that CT molecules with a large twist angle can emit efficient and short-lifetime (a few microseconds) TADF when the emission peak energy is high enough and the (LE)-L-3 state is higher than the (CT)-C-3 state.. |
| 839. | Yan-qiong Zheng, William J. Potscavage, Qi-sheng Zhang, Takeshi Komino, Masatsugu Taneda, Chihaya Adachi, Comparison of small amounts of polycrystalline donor materials in C-70-based bulk heterojunction photovoltaics and optimization of dinaphthothienothiophene based photovoltaic, ORGANIC ELECTRONICS, 10.1016/j.orgel.2014.01.012, 15, 4, 878-885, 2014.04, Comparative studies of the effects of a series of polycrystalline donors on the performance of 95 wt.%-C-70-based bulk-heterojunction (BHJ) photovoltaics were conducted. A BHJ based on the wide band-gap molecule dinaphthothienothiophene (DNTT) shows power conversion efficiency (eta(PCE)) of up to 4.28%. The photovoltaic parameters are superior to those of devices using the similar molecule pentacene (PEN) or polycrystalline copper phthalocyanine (CuPc) for donor concentrations from 5 to 30 wt.%. The low-lying DNTT ionization potential and the high mu(h) in the DNTT blend support the excellent DNTT device performance. The low performance of BHJs with 5 wt.% PEN and 5 wt.% CuPc may stem from strong exciplex recombination in the PEN: C-70 blend and limited hole mobility combined with geminate polaron-pair recombination in the CuPc: C-70 blend. The zero-field hole mobility of the blends with 5 wt.% donor has a positive correlation with the corresponding device performance. The eta(PCE) of a 5 wt.%-DNTT BHJ cell was improved to 4.92% by optimizing the cathode buffer layer. (C) 2014 Elsevier B.V. All rights reserved.. |
| 840. | Kuniaki Endo, Chihaya Adachi, Enhanced out-coupling efficiency of organic light-emitting diodes using an nanostructure imprinted by an alumina nanohole array, APPLIED PHYSICS LETTERS, 10.1063/1.4869468, 104, 12, 2014.03, We demonstrate organic light-emitting diodes (OLEDs) with enhanced out-coupling efficiency containing nanostructures imprinted by an alumina nanohole array template that can be applied to large-emitting-area and flexible devices using a roll-to-roll process. The nanostructures are imprinted on a glass substrate by an ultraviolet nanoimprint process using an alumina nanohole array mold and then an OLED is fabricated on the nanostructures. The enhancement of out-coupling efficiency is proportional to the root-mean-square roughness of the nanostructures, and a maximum improvement of external electroluminescence quantum efficiency of 17% is achieved. The electroluminescence spectra of the OLEDs indicate that this improvement is caused by enhancement of the out-coupling of surface plasmon polaritons. (C) 2014 AIP Publishing LLC.. |
| 841. | Kunihisa Kato, Yoshika Hatasako, Michitaka Uchino, Yasukazu Nakata, Yoshinori Suzuki, Teruaki Hayakawa, Chihaya Adachi, Koji Miyazaki, Flexible Porous Bismuth Telluride Thin Films with Enhanced Figure of Merit using Micro-Phase Separation of Block Copolymer, ADVANCED MATERIALS INTERFACES, 10.1002/admi.201300015, 1, 2, 2014.04. |
| 842. | Chihaya Adachi, Third-generation organic electroluminescence materials, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.7567/JJAP.53.060101, 53, 6, 2014.06, Currently, organic light-emitting diodes (OLEDs) have reached the stage of commercialization, and there are intense efforts to use them in various applications from small-and medium-sized mobile devices to illumination equipment and large TV screens. In particular, phosphorescent materials have become core OLED materials as alternatives to the conventionally used fluorescent materials because devices made with phosphorescent materials exhibit excellent light-emitting performance. However, phosphorescent materials have several problems, such as their structure being limited to organic metal compounds containing rare metals, for example, Ir, Pt, and Os, and difficulty in realizing stable blue light emission, so the development of new materials is necessary. In this article, I will review next-generation OLEDs using a new light-emitting mechanism called thermally activated delayed fluorescence (TADF). Highly efficient TADF, which was difficult to realize with conventional technologies, has been achieved by optimizing molecular structures. This has led to the realization of ultimate next-generation OLEDs that are made of common organic compounds and can convert electricity to light at an internal quantum efficiency of nearly 100%. (C) 2014 The Japan Society of Applied Physics. |
| 843. | Takehiro Takahashi, Katsuyuki Shizu, Takuma Yasuda, Kazunori Togashi, Chihaya Adachi, Donor-acceptor-structured 1,4-diazatriphenylene derivatives exhibiting thermally activated delayed fluorescence: design and synthesis, photophysical properties and OLED characteristics, SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 10.1088/1468-6996/15/3/034202, 15, 3, 34202, 2014.06, A new series of luminescent 1,4-diazatriphenylene (ATP) derivatives with various peripheral donor units, including phenoxazine, 9,9-dimethylacridane and 3-(diphenylamino)carbazole, is synthesized and characterized as thermally activated delayed fluorescence (TADF) emitters. The influence of the donor substituents on the electronic and photophysical properties of the materials is investigated by theoretical calculations and experimental spectroscopic measurements. These ATP-based molecules with donor-acceptor-donor (D-A-D) structures can reduce the singlet-triplet energy gap (0.04-0.26 eV) upon chemical modification of the ATP core, and thus exhibit obvious TADF characteristics in solution and doped thin films. As a demonstration of the potential of these materials, organic light-emitting diodes containing the D-A-D-structured ATP derivatives as emitters are fabricated and tested. External electroluminescence quantum efficiencies above 12% and 8% for green- and sky-blue-emitting devices, respectively, are achieved.. |
| 844. | Hiroshi Fujimoto, Tomohiko Edura, Takuya Miyayama, Noriaki Sanada, Chihaya Adachi, Accurate measurement of dopant concentration in organic light-emitting diodes by combining high-performance liquid chromatography and TOF-SIMS, JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B, 10.1116/1.4871756, 32, 3, 2014.05, The authors report the use of high-performance liquid chromatography (HPLC) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) utilizing a gas cluster ion beam to accurately measure the dopant concentration and its depth profile in organic thin films used for organic light-emitting diodes. The total dopant concentrations estimated by HPLC for films of 4,4'-bis(carbazol-9-yl) biphenyl (CBP) doped with tris(2-phenylpyridinato)iridium(III) (Ir(ppy)(3)) are consistent with those measured by quartz crystal microbalances (QCMs) during the deposition. Concentrations measured for Ir(ppy) 3: CBP films by HPLC and TOF-SIMS show a nearly linear relationship in the range of 1-8 wt. %. At concentrations higher than 8 wt. %, TOF-SIMS values significantly deviate because of the matrix effect. The depth profile of the dopant concentration measured by TOF-SIMS was in good agreement with that measured by QCMs during film deposition for concentrations below 8 wt. %. These methods are especially useful for comparing the dopant concentration of films deposited in different batches and equipment. (C) 2014 American Vacuum Society.. |
| 845. | Hiroshi Ohkuma, Tetsuya Nakagawa, Katsuyuki Shizu, Takuma Yasuda, Chihaya Adachi, Thermally Activated Delayed Fluorescence from a Spiro-diazafluorene Derivative, CHEMISTRY LETTERS, 10.1246/cl.140360, 43, 7, 1017-1019, 2014.07, A Spiro compound DPAA-AF combining an electron-accepting diazafluorene unit and an electron-donating bis(diphenylamino)acridane unit has been synthesized and used as an emitter in organic light-emitting diodes. DPAA-AF exhibits efficient thermally activated delayed fluorescence, and a device based on this compound emits blue-greenish electroluminescence with a maximum external quantum efficiency of 9.6%.. |
| 846. | Motoyuki Uejima, Tohru Sato, Masahiro Detani, Atsushi Wakamiya, Furitsu Suzuki, Hajime Suzuki, Tatsuya Fukushima, Kazuyoshi Tanaka, Yasujiro Murata, Chihaya Adachi, Hironori Kaji, A designed fluorescent anthracene derivative: Theory, calculation, synthesis, and characterization, CHEMICAL PHYSICS LETTERS, 10.1016/j.cplett.2014.04.017, 602, 80-83, 2014.05, 5,11-Bis(phenylethynyl) benzo[1,2-f: 4,5-f'] diisoindole-1,3,7,9(2H,8H)-tetraone 1H was designed as an application of the theoretical design principle for fluorescent molecules which is derived from the vibronic coupling density analysis. For solubility reasons, tertiary-butylated 1H, 2,8-di-tert-butyl-5,11-bis(phenylethynyl)benzo[1,2-f: 4,5-f'] diisoindole-1,3,7,9(2H,8H)-tetraone 1 was synthesized and its fluorescence properties were measured. It is found that the photoluminescence quantum yield of 1 was 96%. We discuss the rationale for designing 1H as a highly efficient fluorescent molecule, and compare the theoretical calculations for 1 with the observed absorption and photoluminescence spectra. (C) 2014 Elsevier B.V. All rights reserved.. |
| 847. | Takahiro Komori; Hajime Nakanotani; Takuma Yasuda; Chihaya Adachi, Light-emitting organic field-effect transistors based on highly luminescent single crystals of thiophene/phenylene co-oligomers, J. Mater. Chem. C,, 10.1039/C4TC00164H, 2, 4918-4921, 2014.04. |
| 848. | Sae Youn Lee; Takuma Yasuda; Yu Seok Yang; Qisheng Zhang; Chihaya Adachi, Luminous Butterflies: Efficient Exciton Harvesting by Benzophenone Derivatives for Full-Color Delayed Fluorescence OLEDs, Angew. Chem. Int. Ed., 10.1002/ange.201402992, 126, 25, 6520-6524, 2014.05. |
| 849. | Kenji Kawano, Kaori Nagayoshi, Takeyuki Yamaki, Chihaya Adachi, Fabrication of high-efficiency multilayered organic light-emitting diodes by a film transfer method, ORGANIC ELECTRONICS, 10.1016/j.orgel.2014.04.035, 15, 7, 1695-1701, 2014.07, In this paper, we report the fabrication of small-molecule-based thin-film layers with a thickness of several tens of nanometers on a release layer by bar coating and subsequent stacking onto other organic layers by the developed film transfer method using driving belts and rollers as a prototype roll-to-roll technique. We use novel thermally activated delayed fluorescence (TADF) materials in this process, achieving multilayered organic light-emitting diodes (OLEDs) with high external quantum efficiency (EQE), which is comparable to those of OLEDs prepared by conventional vacuum deposition. The developed film transfer method shows great potential to realize OLEDs with high efficiency at low cost. (C) 2014 Elsevier B.V. All rights reserved.. |
| 850. | Takeshi Komino, Hiroyuki Tanaka, Chihaya Adachi, Selectively Controlled Orientational Order in Linear-Shaped Thermally Activated Delayed Fluorescent Dopants, CHEMISTRY OF MATERIALS, 10.1021/cm500802p, 26, 12, 3665-3671, 2014.06, The orientational order of a linear-shaped thermally activated delayed fluorescent dopant 10-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-10H-phenoxazine (PXZ-TRZ) was selectively controlled in a randomly oriented host matrix composed of 3,3-di(9H-carbazol-9-yl)biphenyl (mCBP) by varying the temperature during deposition of the thin films. Although the molecular orientation of mCBP was random at deposition temperatures ranging from 200 to 300 K (orientational disorder), PXZ-TRZ molecules oriented horizontal to the substrate in this temperature range (high orientational order). This indicates that the orientational order was dominated by the kinetic behavior of PXZ-TRZ at the film surface rather than by randomization caused by aggregation of PXZ-TRZ and mCBP molecules. Using an orientation-controlled 6 wt % PXZ-TRZ:mCBP film as an emitting layer, we fabricated organic light-emitting diodes (OLEDs). The horizontal orientation of the dopants enhanced the external electroluminescence quantum efficiency of the OLED by 24% compared with that of the corresponding OLED with slightly vertical orientation. An optical simulation found that the enhancement originates mainly from the improvement of the light out-coupling efficiency.. |
| 851. | Gabor Mehes, Kenichi Goushi, William J. Potscavage, Chihaya Adachi, Influence of host matrix on thermally-activated delayed fluorescence: Effects on emission lifetime, photoluminescence quantum yield, and device performance, ORGANIC ELECTRONICS, 10.1016/j.orgel.2014.05.027, 15, 9, 2027-2037, 2014.09, The influence of the host molecules on the photoluminescent (PL) and electroluminescent (EL) properties of organic light-emitting diode (OLED) emitters showing efficient thermally-activated delayed fluorescence (TADF) has yet to be investigated in detail. Here we demonstrate that the choice of host can cause large variations in the PL quantum yield (Phi(PL) similar to 15-70%) and delayed PL transient decay (tau(del) similar to 2-70 ms) of a spiro-acridine-based TADF guest. We show that the effect of exciplex formation on Phi(PL) must be considered even at low concentrations of the TADF guest. Using the same TADF guest but changing the host layer, we are able to greatly vary the PL transient decay time from similar to 4 to similar to 70 ms while maintaining a high Phi(PL) similar to 70%, which can lead to new applications. Detailed spectral characterization during PL decay reveals a gradually increasing singlet-triplet energy gap (Delta E-ST) as the origin of these observations. The time-varying Delta E-ST is explained based on dipole interactions between the host and guest molecules. Finally, PL and electrical considerations for host selection are discussed based on the performance of OLED devices. (C) 2014 Elsevier B.V. All rights reserved.. |
| 852. | Ryoichi Ishimatsu; Shigeyuki Matsunami; Takashi Kasahara; Jun Mizuno; Tomohiko Edura; Chihaya Adachi; Koji Nakano; Toshihiko Imato, Electrogenerated Chemiluminescence of Donor–Acceptor Molecules with Thermally Activated Delayed Fluorescence, Angew. Chem., 10.1002/ange.201402615, 126, 27, 7113-7116, 2014.05. |
| 853. | Jun-ichi Nishide, Hajime Nakanotani, Yasuhide Hiraga, Chihaya Adachi, High-efficiency white organic light-emitting diodes using thermally activated delayed fluorescence, APPLIED PHYSICS LETTERS, 10.1063/1.4882456, 104, 23, 2014.06, White organic light-emitting diodes (WOLEDs) have attracted much attention recently, aimed for next-generation lighting sources because of their high potential to realize high electroluminescence efficiency, flexibility, and low-cost manufacture. Here, we demonstrate high-efficiency WOLED using red, green, and blue thermally activated delayed fluorescence materials as emissive dopants to generate white electroluminescence. The WOLED has a maximum external quantum efficiency of over 17% with Commission Internationale de l'Eclairage coordinates of (0.30, 0.38). (C) 2014 AIP Publishing LLC.. |
| 854. | Le Zhang, Hajime Nakanotani, Kou Yoshida, Chihaya Adachi, Analysis of alternating current driven electroluminescence in organic light emitting diodes: A comparative study, ORGANIC ELECTRONICS, 10.1016/j.orgel.2014.05.009, 15, 8, 1815-1821, 2014.08, The alternating current (AC) responses of double-injection and double-insulated organic light-emitting diodes (OLEDs) were investigated and compared. To reveal the electroluminescent (EL) processes in these devices, the AC voltage and frequency dependence of the EL intensity and capacitive current were studied in the time domain with a focus on phase difference analysis. It was found that the voltage-dependent transit time and frequencydependent carrier distribution were important for the AC-driven performance of the double-injection OLEDs. In contrast, although the double-insulated OLEDs shared some similarities with the double-injection OLEDs, they had some unique characteristics, which were the absence of resistive current and phase shift of EL profiles. It was revealed that the EL in the double-insulated OLEDs was driven by the displacement current generated by the ionization of the doped layers, which, however, formed space charge regions and undermined the EL emission. The space charge redistributed the electric field across the devices after the initiation of EL, making the EL maintain for a limited time interval. This effect was significant under low frequency and high AC voltage. Comparing the phase difference between both devices, it was indicated that the space charge effect was responsible for the observed EL phase shift and the asymmetric EL profiles at low frequency and high AC voltage in the double-insulated OLEDs. The proposed model was also of help to understand the EL saturation phenomena with AC frequency and voltage in those devices. (C) 2014 Elsevier B. V. All rights reserved.. |
| 855. | Christian Mayr, Sae Youn Lee, Tobias D. Schmidt, Takuma Yasuda, Chihaya Adachi, Wolfgang Bruetting, Efficiency Enhancement of Organic Light-Emitting Diodes Incorporating a Highly Oriented Thermally Activated Delayed Fluorescence Emitter, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.201400495, 24, 33, 5232-5239, 2014.09, An organic light-emitting diode (OLED) with the blue emitter CC2TA showing thermally activated delayed fluorescence (TADF) is presented exhibiting an external quantum efficiency (eta(EQE).) of 11% +/- 1%, which clearly exceeds the classical limit for fluorescent OLEDs. The analysis of the emission layer by angular dependent photoluminescence (PL) measurements shows a very high degree of 92% horizontally oriented transition dipole moments. Excited states lifetime measurements of the prompt fluorescent component under PL excitation yield a radiative quantum efficiency of 55% of the emitting species. Thus, the radiative exciton fraction has to be significantly higher than 25% due to TADF. Performing a simulation based efficiency analysis for the OLED under investigation allows for a quantification of individual contributions to the efficiency increase originating from horizontal emitter orientation and TADF. Remarkably, the strong horizontal emitter orientation leads to a light-outcoupling efficiency of more than 30%.. |
| 856. | Takashi Kasahara, Shigeyuki Matsunami, Tomohiko Edura, Ryoichi Ishimatsu, Juro Oshima, Miho Tsuwaki, Toshihiko Imato, Shuichi Shoji, Chihaya Adachi, Jun Mizuno, Multi-color microfluidic electrochemiluminescence cells, SENSORS AND ACTUATORS A-PHYSICAL, 10.1016/j.sna.2014.04.039, 214, 225-229, 2014.08, We demonstrated multi-color microfluidic electrochemiluminescence (ECL) cells. 5,6,11,12-Tetraphenylnaphthacene (rubrene), 9,10-diphenylanthracene (DPA), tetraphenyldibenzoperiflanthene (DBP)-doped rubrene, and 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) dissolved in a mixed organic solvent of 1,2-dichlorobenzene and acetonitrile in the ratio of 2:1 (v/v) were used as yellow, blue, red, and green ECL solutions, respectively. Light emissions were confirmed using simple-structured ECL cells consisting of two indium tin oxide (ITO) coated glass substrates with an SU-8 spacer of thickness varying from 0.9 to 6 mu m. The SU-8-based microfluidic ECL cells were fabricated using photolithography and heterogeneous bonding techniques through the use of epoxy-and amine-terminated self-assembled monolayers. The emitting layers were formed on-demand by injecting the chosen ECL solutions into the microchannels sandwiched between ITO anode and cathode pairs. Multi-color ECL was successfully obtained at the light-emitting pixels. The microfluidic ECL cells with DBP-doped rubrene solution showed a maximum luminance of 11.6 cd/m(2) and the current efficiency of ca. 0.32 cd/A at 8V. We expect that the proposed microfluidic device will be a highly promising technology for liquid-based light-emitting applications. (C) 2014 Elsevier B.V. All rights reserved.. |
| 857. | Miho Tsuwaki, Takashi Kasahara, Tomohiko Edura, Shigeyuki Matsunami, Juro Oshima, Shuichi Shoji, Chihaya Adachi, Jun Mizuno, Fabrication and characterization of large-area flexible microfluidic organic light-emitting diode with liquid organic semiconductor, SENSORS AND ACTUATORS A-PHYSICAL, 10.1016/j.sna.2014.05.032, 216, 231-236, 2014.09, We propose simple and high-throughput fabrication of large-area flexible microfluidic organic light-emitting diodes (microfluidic OLEDs). Flexible electro-SU-8-microchannels with a liquid emission layer were fabricated by the following four steps: (a) screen printing for transparent electrodes, (b) novel belttransfer exposure for SU-8, (c) heterogeneous low-temperature bonding using self-assembled monolayers (SAMs), and (d) injecting a liquid emitter into the microchannels.1-Pyrenebutyric acid 2-ethylhexyl ester (PLQ), which is on of liquid organic semiconductors, was used as a liquid emitter. The liquid emitter successfully filled the flexible microchannels, and electroluminescence was obtained both in flat and curved states. The proposed microfluidic OLED is applicable for future flexible posters or displays, and can be adopted around curved surfaces. (C) 2014 Elsevier B.V. All rights reserved.. |
| 858. | Hajime Nakanotani, Takahiro Higuchi, Taro Furukawa, Kensuke Masui, Kei Morimoto, Masaki Numata, Hiroyuki Tanaka, Yuta Sagara, Takuma Yasuda, Chihaya Adachi, High-efficiency organic light-emitting diodes with fluorescent emitters, NATURE COMMUNICATIONS, 10.1038/ncomms5016, 5, 4016, 4016, 2014.05, Fluorescence-based organic light-emitting diodes have continued to attract interest because of their long operational lifetimes, high colour purity of electroluminescence and potential to be manufactured at low cost in next-generation full-colour display and lighting applications. In fluorescent molecules, however, the exciton production efficiency is limited to 25% due to the deactivation of triplet excitons. Here we report fluorescence-based organic light-emitting diodes that realize external quantum efficiencies as high as 13.4-18% for blue, green, yellow and red emission, indicating that the exciton production efficiency reached nearly 100%. The high performance is enabled by utilization of thermally activated delayed fluorescence molecules as assistant dopants that permit efficient transfer of all electrically generated singlet and triplet excitons from the assistant dopants to the fluorescent emitters. Organic light-emitting diodes employing this exciton harvesting process provide freedom for the selection of emitters from a wide variety of conventional fluorescent molecules.. |
| 859. | Akitsugu Niwa, Takashi Kobayashi, Takashi Nagase, Kenichi Goushi, Chihaya Adachi, Hiroyoshi Naito, Temperature dependence of photoluminescence properties in a thermally activated delayed fluorescence emitter, APPLIED PHYSICS LETTERS, 10.1063/1.4878397, 104, 21, 2014.05, Using steady-state and time-resolved photoluminescence (PL) spectroscopy, we have investigated the temperature dependence of PL properties of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), which have a small energy gap between its singlet and triplet excited states and thus exhibits efficient thermally activated delayed fluorescence [H. Uoyama et al., Nature 492, 235 (2012)]. Below around 100 K, PL quantum efficiency of 4CzIPN thin films is largely suppressed and strong photoexcitation intensity dependence appears. These features can be explained by using rate equations for the densities of singlet and triplet excited states considering a triplet-triplet annihilation process. (C) 2014 AIP Publishing LLC.. |
| 860. | Rampal Pandey; Gábor Méhes; Amit Kumar; Rakesh Kumar Gupta; Chihaya Adachi; Daya Shankar Pandey, Structural and mechanistic insights into an Fe3+-triggered quinazoline based molecular rotor, Chem. Comm., 10.1039/C4CC01917B, 50, 8032-8035, 2014.05. |
| 861. | Hiroyuki Tanaka, Katsuyuki Shizu, Hajime Nakanotani, Chihaya Adachi, Dual Intramolecular Charge-Transfer Fluorescence Derived from a Phenothiazine-Triphenyltriazine Derivative, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp501017f, 118, 29, 15985-15994, 2014.07, A material containing a phenothiazine (PTZ) electron donor unit and 2,4,6-triphenyl-1,3,5-triazine (TRZ) electron acceptor unit, PTZ-TRZ, which exhibits thermally activated delayed fluorescence (TADF) was developed. Density functional theory calculations revealed the existence of two ground-state conformers with different energy gaps between the lowest singlet excited state and lowest triplet excited state (1.14 and 0.18 eV), which resulted from the distortion of PTZ, as confirmed by X-ray structure analysis. PTZ-TRZ in toluene solution showed two broad, structureless emissions, confirming the existence of two different excited states. From detailed analyses of the absorption and photoluminescence spectra, we determined that both emissions were intramolecular charge-transfer (ICT) fluorescence. Therefore, the excited-state conformers of PTZ-TRZ resulted in dual ICT fluorescence. Because previously reported dual fluorescence from single molecules involves locally excited and ICT fluorescence, the dual ICT fluorescence from PTZ-TRZ is novel. Temperature-dependence of transient PL spectra of a 2 wt % PTZ-TRZ-doped film in 3,3'-bis(N-carbazolyl)-1,1'-biphenyl measured by a streak camera revealed that the former and latter emissions were independent of and dependent on the film temperature, respectively. This confirms that the dual fluorescence involves TADF characteristics. An organic light-emitting diode containing PTZ-TRZ exhibited a maximum external quantum efficiency of 10.8 +/- 0.596 with dual ICT fluorescence.. |
| 862. | Ryota Kabe, Xinliang Feng, Chihaya Adachi, Klaus Muellen, Exfoliation of Graphite into Graphene in Polar Solvents Mediated by Amphiphilic Hexa-peri-hexabenzocoronene, CHEMISTRY-AN ASIAN JOURNAL, 10.1002/asia.201402535, 9, 11, 3125-3129, 2014.11, A water-soluble surfactant consisting of hexa-peri-hexabenzocoronene (HBC) as hydrophobic aromatic core and hydrophilic carboxy substituents was synthesized. It exhibited a self-assembled nanofiber structure in the solid state. Profiting from the pi interactions between the large aromatic core of HBC and graphene, the surfactant mediated the exfoliation of graphite into graphene in polar solvents, which was further stabilized by the bulky hydrophilic carboxylic groups. A graphene dispersion with a concentration as high as 1.1 mgL(-1) containing 2-6 multilayer nanosheets was obtained. The lateral size of the graphene sheets was in the range of 100-500 nm based on atomic force microscope (AFM) and transmission electron microscope (TEM) measurements.. |
| 863. | Wu Shuang-Hong, Ryosuke Nakamichi, Masatsugu Taneda, Zhang Qi-Sheng, Chihaya Adachi, Introduction of F-4-TCNQ/MoO3 layers for thermoelectric devices based on pentacene, CHINESE PHYSICS B, 10.1088/1674-1056/23/9/098502, 23, 9, 98502, 2014.09, We introduced a dual electron accepting layer composed of tetrafluoro-tetracyanoquinodimethane (F-4-TCNQ) and MoO3 for thermoelectric devices based on a pentacene layer. We found that the power factor is enhanced by placing an F-4-TCNQ layer directly in contact with the pentacene layer and it is also enhanced by placing a MoO3 layer between the F-4-TCNQ layer and the Au electrode. By examining the contact resistance using a field effect transistor and a hole-only diode, we confirmed that the hole injection is improved due to the reduction of contact resistance at the interface between the MoO3 layer and the Au electrode.. |
| 864. | Hiroshi Fujimoto, William J. Potscavage, Tomohiko Edura, Chihaya Adachi, Analysis of electron traps formed in organic films with a sputtered cathode, ORGANIC ELECTRONICS, 10.1016/j.orgel.2014.08.021, 15, 11, 2783-2791, 2014.11, To understand why performance degradation is reduced for sputtered cathodes on organic devices when the electron transport layer (ETL) is doped with Li, we analyze electron-only devices using the thermally stimulated current (TSC) technique and modeling of temperature-dependent current-voltage characteristics with a trapped-charge-limited current (TCLC) model. The combined results suggest that the trap density measured by TSC might also include a portion of the density of the hopping sites in the lowest unoccupied molecular orbital levels, which contributes to charge transport. Compared to undoped devices, doped devices maintain a high density of hopping sites even when the Al is sputtered. We propose that the reduced effect of sputtering on electron injection and transport properties is because radical anions of Alq(3) might still be formed by the strong reducer Li even if the organic material is partially damaged. An additional TSC peak and increased driving voltage for doped tris(8-hydroxyquinoline)aluminum (Alq(3)) as an ETL with a sputtered cathode suggests the formation of new traps possibly because of damage even though the transport is better compared to the undoped device. Such traps are not found in doped bathophenanthroline (Bphen) as an ETL, which shows no change in driving voltage. (C) 2014 Elsevier B.V. All rights reserved.. |
| 865. | Christian Mayr, Masatsugu Taneda, Chihaya Adachi, Wolfgang Bruetting, Different orientation of the transition dipole moments of two similar Pt(II) complexes and their potential for high efficiency organic light-emitting diodes, ORGANIC ELECTRONICS, 10.1016/j.orgel.2014.07.042, 15, 11, 3031-3037, 2014.11, The efficiency of organic light-emitting diodes (OLEDs) is especially limited by their low light outcoupling efficiency. An approach for its enhancement is the use of horizontally oriented emitter molecules with respect to the substrate. In this study we quantitatively determine the orientation of the optical transition dipole moments in doped films of two similar phosphorescent Pt(II) complexes having a linear molecular structure. These emitters are employed in OLED devices and their efficiency is analyzed by optical simulations. For an OLED with slightly more horizontally oriented emitter molecules an external quantum efficiency (eta(EQE)) of 15.8% at low current-density is realized, indicating a relative improvement of outcoupling efficiency of 5.3% compared to the isotropic case. However, a very similar complex adopting isotropic molecular orientation yields eta(EQE) of only 11.5% implying an imperfect charge carrier balance in the OLED device and a shift of the recombination zone. Furthermore, we highlight the enormous potential of horizontal molecular orientation of emitting molecules in OLEDs. (C) 2014 Elsevier B.V. All rights reserved.. |
| 866. | Shuzo Hirata, Kenro Totani, Takashi Yamashita, Chihaya Adachi, Martin Vacha, Large reverse saturable absorption under weak continuous incoherent light, NATURE MATERIALS, 10.1038/NMAT4081, 13, 10, 938-946, 2014.10, In materials showing reverse saturable absorption (RSA), the optical absorbance increases as the power of the light incident on them increases. To date, RSA has only been observed when very intense light sources, such as short-pulse lasers, are used. Here, we show that hydroxyl steroidal matrices embedding properly designed aromatic molecules as acceptors and transition-metal complexes as donors exhibit high RSA on exposure to weak incoherent light at room temperature and in air. Accumulation by photosensitization of long-lived room-temperature triplet excitons in acceptors with a large triplettriplet absorption coefficient allows a nonlinear increase in absorbance also under low-power irradiation conditions. As a consequence, continuous exposure to weak light significantly decreases the transmittance of thin films fabricated with these compounds. These optical limiting properties may be used to protect eyes and light sensors from exposure to intense radiation generated by incoherent sources and for other light-absorption applications that have not been realized with conventional RSA materials.. |
| 867. | Hiroshi Fujimoto, Takuya Miyayama, Noriaki Sanada, Chihaya Adachi, Origin of external quantum efficiency degradation in organic light-emitting diodes with a DC magnetron sputtered cathode, JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B, 10.1116/1.4897920, 32, 6, 60603, 2014.11, This paper characterizes changes in organic light-emitting diodes to better understand the origin of the decrease in external quantum efficiency (eta(ext)) when switching the cathode deposition method from evaporation to DC magnetron sputtering. An increase of driving voltage and a hole-barrier-dependent decrease of eta(ext) when the Al cathode is sputtered suggest that disruption of carrier balance and penetration of holes from the emissive layer (EML) into the electron transport layer (ETL) are significant sources of the device degradation. When the ETL was doped with Li, degradation was suppressed and the increase in driving voltage was drastically reduced although eta(ext) still decreased by 5%-7%. Analysis of the films by time-of-flight secondary ion mass spectrometry indicates that Li diffuses into the EML when Al is sputtered, and Li is shown to act as an exciton quencher that can decrease eta(ext). Doping of the ETL is also used to significantly suppress the performance reduction with sputtered cathodes even when using a phosphorescent emitter having high eta(ext). (C) 2014 American Vacuum Society.. |
| 868. | Seung Kyum Kim, Chang-Hoon Shim, Tomohiko Edura, Chihaya Adachi, Reiji Hattori, Improved organic thin-film transistor characteristics using an elevated-electrode structure, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.7567/JJAP.53.111601, 53, 11, 111601, 2014.11, We propose a new structure for organic thin-film transistors, denoted as "elevated-electrode structure" in which the source and drain electrodes are formed on the elevated insulation layer. Indeed, the experimental data shows that this new structure has more than twice the drain current and mobility of a conventional bottom-structured TFT, this being found to be directly related to the height of the elevated electrode. Moreover, the reproducibility of this data confirms a greater stability than that of either top-contact or bottom-contact devices. (C) 2014 The Japan Society of Applied Physics. |
| 869. | Qisheng Zhang, Hirokazu Kuwabara, William J. Potscavage, Shuping Huang, Yasuhiro Hatae, Takumi Shibata, Chihaya Adachi, Anthraquinone-Based Intramolecular Charge-Transfer Compounds: Computational Molecular Design, Thermally Activated Delayed Fluorescence, and Highly Efficient Red Electroluminescence, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja510144h, 136, 52, 18070-18081, 2014.12, Red fluorescent molecules suffer from large, non-radiative internal conversion rates (k(IC)) governed by the energy gap law. To design efficient red thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs), a large fluorescence rate (k(F)) as well as a small energy difference between the lowest singlet and triplet excited states (Delta E-ST) is necessary. Herein, we demonstrated that increasing the distance between donor (D) and acceptor (A) in intramolecular-charge-transfer molecules is a promising strategy for simultaneously achieving small Delta E-ST and large k(F). Four D-Ph-A-Ph-D-type molecules with an anthraquinone acceptor, phenyl (Ph) bridge, and various donors were designed, synthesized, and compared with corresponding D-A-D-type molecules. Yellow to red TADF was observed from all of them. The k(F) and Delta E-ST values determined from the measurements of quantum yield and lifetime of the fluorescence and TADF components are in good agreement with those predicted by corrected time-dependent density functional theory and are approximatively proportional to the square of the cosine of the theoretical twisting angles between each subunit. However, the introduction of a Ph-bridge was found to enhance k(F) without increasing Delta E-ST. Molecular simulation revealed a twisting and stretching motion of the NC bond in the D-A-type molecules, which is thought to lower Delta E-ST and k(F) but raise k(IC), that was experimentally confirmed in both solution and doped film. OLEDs containing D-Ph-A-Ph-D-type molecules with diphenylamine and bis(4-biphenyl)amine donors demonstrated maximum external quantum efficiencies of 12.5% and 9.0% with emission peaks at 624 and 637 nm, respectively.. |
| 870. | Toshinori Matsushima, Yu Esaki, Chihaya Adachi, Enhancement of the electrical characteristics of metal-free phthalocyanine films using cold isostatic pressing, APPLIED PHYSICS LETTERS, 10.1063/1.4904463, 105, 24, 2014.12, Spatial gaps between grains and other grains, substrates, or electrodes in organic electronic devices are one of the causes of the reduction in the electrical characteristics. In this study, we demonstrate that cold isostatic pressing (CIP) is an effective method to crush the gaps and enhance the electrical characteristics. CIP of metal-free phthalocyanine (H2PC) films induced a decrease in the film thickness by 34%-40% because of the gap crush. The connection of smaller grains into a larger grain and planarization of the film surface were also observed in the CIP film. The crystal axes of the H2PC crystallites were rearranged from the a-axis to the c-axis of the alpha-phase crystal structure in a direction perpendicular to the substrate by CIP, indicating favorable hole injection and transport in this direction because of a better overlap of pi orbitals. Thermally stimulated current measurements showed that deep hole traps disappeared and the total hole-trap density decreased after CIP. These CIP-induced changes of the film thicknesses, crystal axes and the hole traps lead to a marked increase in the hole mobility of the H2PC films from 2.0 x 10(-7) to 4.0 x 10(-4) cm(2)/V s by 2000 times in the perpendicular direction. We believe that these findings are important for unveiling the underlying carrier injection and transport mechanisms of organic films and for enhancing the performance of future organic electronic devices. (C) 2014 AIP Publishing LLC.. |
| 871. | Shuzo Hirata, Yumi Sakai, Kensuke Masui, Hiroyuki Tanaka, Sae Youn Lee, Hiroko Nomura, Nozomi Nakamura, Mao Yasumatsu, Hajime Nakanotani, Qisheng Zhang, Katsuyuki Shizu, Hiroshi Miyazaki, Chihaya Adachi, Highly efficient blue electroluminescence based on thermally activated delayed fluorescence, NATURE MATERIALS, 10.1038/NMAT4154, 14, 3, 330-336, 2015.03, Organic compounds that exhibit highly efficient, stable blue emission are required to realize inexpensive organic light-emitting diodes for future displays and lighting applications. Here, we define the design rules for increasing the electroluminescence efficiency of blue-emitting organic molecules that exhibit thermally activated delayed fluorescence. We show that a large delocalization of the highest occupied molecular orbital and lowest unoccupied molecular orbital in these charge-transfer compounds enhances the rate of radiative decay considerably by inducing a large oscillator strength even when there is a small overlap between the two wavefunctions. A compound based on our design principles exhibited a high rate of fluorescence decay and efficient up-conversion of triplet excitons into singlet excited states, leading to both photoluminescence and internal electroluminescence quantum yields of nearly 100%.. |
| 872. | Yuta Sagara, Katsuyuki Shizu, Hiroyuki Tanaka, Hiroshi Miyazaki, Kenichi Goushi, Hironori Kaji, Chihaya Adachi, Highly Efficient Thermally Activated Delayed Fluorescence Emitters with a Small Singlet-Triplet Energy Gap and Large Oscillator Strength, CHEMISTRY LETTERS, 10.1246/cl.141054, 44, 3, 360-362, 2015.03, A strategy for designing highly efficient thermally activated delayed fluorescence (TADF) emitters was reported. TADF emitters with donor-acceptor-donor (D-A-D)-type structures showed highly efficient TADF because of their small singlet-triplet energy gap and large oscillator strength. An organic light-emitting diode containing a D-A-D-type TADF emitter, cis-BOX2, exhibited a high external electroluminescence quantum efficiency of 17.6%.. |
| 873. | Yoshitake Suzuki; Qisheng Zhang; Chihaya Adachi, Solution-Processable Host Material of 1,3-Bis{3-[3-(9-carbazolyl)phenyl]-9-carbazolyl}benzene and its Application in Organic Light-Emitting Diodes Employing Thermally Activated Delayed Fluorescence, J. Mater. Chem. C, 10.1039/C4TC02211D, 3, 1700-1706, 2014.12. |
| 874. | Katsuyuki Shizu, Hiroyuki Tanaka, Motoyuki Uejima, Tohru Sato, Kazuyoshi Tanaka, Hironori Kaji, Chihaya Adachi, Strategy for Designing Electron Donors for Thermally Activated Delayed Fluorescence Emitters, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp511061t, 119, 3, 1291-1297, 2015.01, Thermally activated delayed fluorescence (TADF) emitters are promising dopants for organic light-emitting diodes, including those containing highly twisted donor-acceptor-type structures. However, highly twisted structures limit the variety of chemical structures applicable as TADF emitters. We present a strategy for designing electron donors that can eliminate this requirement and increase the structural diversity of TADF emitters. Using this strategy, we developed an electron donor containing carbazolyl and diphenylamino groups by carefully controlling its electron-donating ability. By combining this donor with a quinoxaline-based acceptor, we obtained the efficient green TADF emitter, N-3,N-3,N-6,N-6-tetraphenyl-9-(4-(quinoxalin-6-yl)phenyl)-9H-carbazole-3,6-diamine (DACQ), without a highly twisted structure. DACQ exhibits high photoluminescence and electroluminescence efficiencies, comparable to those of a highly twisted TADF emitter containing the same electron-accepting unit. Quantum chemical calculations showed that the diphenylamino groups within the carbazolyl moiety effectively withdraw the HOMO distribution. This reduces the singlet-triplet energy gap, thus inducing TADF. The photophysical properties of TADF compounds depend on the twisting angle between the electron-donating and accepting units. Eliminating the highly twisted structure increases the diversity of potential TADF emitters and allows their photophysical properties to be controlled by changing the twisting angle.. |
| 875. | Katsuyuki Shizu, Motoyuki Uejima, Hiroko Nomura, Tohru Sato, Kazuyoshi Tanaka, Hironori Kaji, Chihaya Adachi, Enhanced Electroluminescence from a Thermally Activated Delayed-Fluorescence Emitter by Suppressing Nonradiative Decay, PHYSICAL REVIEW APPLIED, 10.1103/PhysRevApplied.3.014001, 3, 1, 2015.01, Thermally activated delayed-fluorescence (TADF) is a promising approach for realizing highly efficient organic light-emitting diodes (OLEDs). By controlling the spatial overlap between the frontier orbitals to suppress nonradiative decay, we develop a highly efficient TADF emitter, N-1-[4-(4,6-diphenyl-1,3, 5-triazin-2-yl)phenyl]-N-1-[4-(diphenylamino)-phenyl]-N-4, N-4-diphenylbenzene-1,4-diamine (DPA-TRZ). DPA-TRZ exhibits a photoluminescence quantum efficiency of 100% when doped into a host material, suggesting that nonradiative decay from its excited states is completely suppressed. Transient photoluminescence measurements confirm that DPA-TRZ emits TADF in a doped film. An OLED containing DPA-TRZ as a green emitter shows a maximum external quantum efficiency of 13.8%, which exceeds the theoretical limit for conventional fluorescent OLEDs. This high efficiency results from the effective generation of TADF and suppressed nonradiative decay in DPA-TRZ. Our molecular design strategy based on quantum chemistry provides a rational approach to control radiative and nonradiative decays for optimizing TADF materials.. |
| 876. | Rong Liu; Ryoichi Ishimatsu; Masayuki Yahiro; Chihaya Adachi; Koji Nakano; Toshihiko Imato, Photometric flow injection determination of phosphate on a PDMS microchip using an optical detection system assembled with an organic light emitting diode and an organic photodiode, Talanta, 10.1016/j.talanta.2014.10.055, 134, 37-47, 2015.01. |
| 877. | Yutaka Noguchi, Hyung-Jun Kim, Ryuta Ishino, Kenichi Goushi, Chihaya Adachi, Yasuo Nakayama, Hisao Ishii, Charge carrier dynamics and degradation phenomena in organic light-emitting diodes doped by a thermally activated delayed fluorescence emitter, ORGANIC ELECTRONICS, 10.1016/j.orgel.2014.12.009, 17, 184-191, 2015.02, We report on the charge carrier dynamics and their degradation phenomena in an organic light-emitting diode (OLED) doped by a thermally activated delayed fluorescence emitter; (4s, 6s)-2,4,5,6-tetra(9H-carbazol-9-yl) isophthalonitrile (4CzIPN). Displacement current measurement (DCM) data revealed the presence of negative interface charge originating from the spontaneous orientation polarization of the electron transport layer (ETL), 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl) benzene. The negative interface charge acts as a hole reservoir and thus confines the recombination zone near the emission layer (EML); 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP):4CzIPN (5 wt%)/ETL interface. By keeping the recombination zone far from the hole transport layer, 4,40-bis[N-(1-naphthyl)-N-phenylamino]- biphenyl (alpha-NPD), a better electroluminescence efficiency is expected because the Dexter energy transfer from the triplet state of 4CzIPN to that of alpha-NPD is suppressed. Moreover, we found an excellent linear relation between the accumulated hole amount and luminance losses owing to device aging. The results are consistent with hole traps originating at the degradation products of CBP as the main factor of device degradation. We suggest device architectures based on the charge carrier dynamics for better efficiency and lifetime. (C) 2014 Elsevier B.V. All rights reserved.. |
| 878. | Jiyoung Lee; Katsuyuki Shizu; Hiroyuki Tanaka; Hajime Nakanotani; Takuma Yasuda; Hironori Kaji; Chihaya Adachi, Controlled emission color and singlet-triplet energy gap of dihydrophenazine-based thermally activated delayed fluorescence emitters, J. Mater. Chem. C, 10.1039/C4TC02530J, 3, 2175-2181, 2015.01. |
| 879. | Yumi Sakai; Yuta Sagara; Hiroko Nomura; Nozomi Nakamura; Yoshitake Suzuki; Hiroshi Miyazaki; Chihaya Adachi, Zinc complexes exhibiting highly efficient thermally activated delayed fluorescence and their application to organic light-emitting diodes, Chem. Comm., 10.1039/C4CC09403D, 51, 3181-3184, 2015.01. |
| 880. | Sae Youn Lee; Takuma Yasuda; In Seob Park; Chihaya Adachi, X-shaped benzoylbenzophenone derivatives with crossed donors and acceptors for highly efficient thermally activated delayed fluorescence, Dalton Transactions, 10.1039/C4DT03608E, 44, 8356-8359, 2015.01. |
| 881. | Kyohei Hayashi, Hajime Nakanotani, Munetomo Inoue, Kou Yoshida, Oleksandr Mikhnenko, Thuc-Quyen Nguyen, Chihaya Adachi, Suppression of roll-off characteristics of organic light-emitting diodes by narrowing current injection/transport area to 50 nm, APPLIED PHYSICS LETTERS, 10.1063/1.4913461, 106, 9, 2015.03, Using e-beam nanolithography, the current injection/transport area in organic light-emitting diodes (OLEDs) was confined into a narrow linear structure with a minimum width of 50 nm. This caused suppression of Joule heating and partial separation of polarons and excitons, so the charge density where the electroluminescent efficiency decays to the half of the initial value (J(0)) was significantly improved. A device with a narrow current injection width of 50 nm exhibited a J(0) that was almost two orders of magnitude higher compared with that of the unpatterned OLED. (C) 2015 AIP Publishing LLC.. |
| 882. | Hiroyuki Tanaka, Katsuyuld Shizu, Jiyoung Lee, Chihaya Adachi, Effect of Atom Substitution in Chalcogenodiazole-Containing Thermally Activated Delayed Fluorescence Emitters on Radiationless Transition, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/jp510751n, 119, 6, 2948-2955, 2015.02, Radiationless transition between the lowest singlet (S-1) and triplet (T1) excited states in the thermally activated delayed fluorescence (TADF) were investigated with respect to molecular design. The photophysical, transient photoluminescence and electroluminescence (EL) characteristics of two chalcogenodiazole-containing TADF emitters were compared. These contained 1,3,4-oxadiazole or 1,3,4-thiadiazole. The effect of substituting oxygen with sulfur on TADF was caused by an electron-pair-accepting conjugative effect. This effect resulted from the vacant 3d-orbitals of divalent sulfur in the thiadiazole heteroring. Atom substitution narrowed the gap between the highest occupied and lowest unoccupied molecular orbital energy levels, and enhanced S-1 -> T-1 intersystem crossing. These effects resulted from the enhanced acceptor strength and orbital angular momentum by the vacant 3d-orbitals of sulfur. Atom substitution increased the contribution of the delayed fluorescence component to the total EL efficiency (65.1% -> 78.0%). This resulted from enhanced reverse intersystem crossing, because of the reduced energy gap between S-1 and T-1.. |
| 883. | Ju-Hyung Kim, Munetomo Inoue, Li Zhao, Takeshi Komino, Soonmin Seo, Jean-Charles Ribierre, Chihaya Adachi, Tunable and flexible solvent-free liquid organic distributed feedback lasers, APPLIED PHYSICS LETTERS, 10.1063/1.4907323, 106, 5, 2015.02, We report on optically pumped blue, green, and red liquid organic distributed feedback (DFB) lasers based on solvent-free fluidic organic semiconductors, and prepared on highly flexible corrugated polymeric patterns. By the appropriate selection of laser dyes doping a liquid 9-(2-ethylhexyl) carbazole host, the lasing wavelength is effectively tuned across the visible spectrum via a cascade energy transfer scheme. We also demonstrate a mechanical tunability of the flexible liquid DFB laser emission, which is due to the deformation of the high-aspect ratio DFB grating under bending. Overall, this work provides an important step in the development of flexible liquid organic optoelectronic devices. (C) 2015 AIP Publishing LLC.. |
| 884. | Munetomo Inoue, Toshinori Matsushima, Hajime Nakanotani, Chihaya Adachi, Introduction of oxygen into organic thin films with the aim of suppressing singlet-triplet annihilation, CHEMICAL PHYSICS LETTERS, 10.1016/j.cplett.2015.02.010, 624, 43-46, 2015.03, Efficient introduction of oxygen into a solid-state organic film is demonstrated by applying a high oxygen pressure of 200 MPa to the film. The oxygen-introduced film shows strong suppression of singlet-triplet annihilation (STA) because triplet excitons are quenched by oxygen introduced inside the film. It is demonstrated that oxygen molecules are uniformly distributed in the film and that oxygen molecules are left in the film to some extent when the film is in a vacuum. The concentration of oxygen inside the film is calculated to be a very high value on the order of 4.4 x 10(20) cm(-3). (C) 2015 Elsevier B.V. All rights reserved.. |
| 885. | Masahiro Misaki, Asami Toba, Daisuke Goto, Chihaya Adachi, Yasuko Koshiba, Kenji Ishida, Yasukiyo Ueda, Laser-Induced Micro-Patterning of Organic Semiconductor Layers for Use in Organic Light-Emitting Diode Displays, ITE Transactions on Media Technology and Applications (MTA), 3, 2, 143-148, 2015.04. |
| 886. | Takashi Kasahara, Shigeyuki Matsunami, Tomohiko Edura, Ryoichi Ishimatsu, Juro Oshima, Miho Tsuwaki, Toshihiko Imato, Shuichi Shoji, Chihaya Adachi, Jun Mizuno, Multi-color microfluidic organic light-emitting diodes based on on-demand emitting layers of pyrene-based liquid organic semiconductors with fluorescent guest dopants, SENSORS AND ACTUATORS B-CHEMICAL, 10.1016/j.snb.2014.09.101, 207, 481-489, 2015.02, In this study, we propose on-demand multi-color microfluidic organic light-emitting diodes (microfluidic OLEDs) using fluorescent guest emitter-doped liquid organic semiconductors. We use 1-pyrenebutyric acid 2-ethylhexyl ester (PLQ) not only for a greenish-blue liquid emitter, but also for a liquid host. 5,12-Diphenyltetracene (DPT), 5,6,11,12-tetraphenyltetracene (rubrene), and tetraphenyldibenzoperiflanthene (DBP) are doped into PLQ to obtain green, yellow, and red liquid emitters, respectively. Single-micrometer-thick SU-8-based microchannels sandwiched between an indium tin oxide (ITO) anode and a 3-aminopropyltriethoxysilane (APTES)-modified ITO cathode are fabricated on a glass substrate using photolithography and heterogeneous bonding techniques, and emitting layers are formed on-demand by simply injecting liquid emitters into the target microchannels. The microfluidic OLEDs with liquid emitters successfully exhibited multi-color electroluminescence (EL) emissions. Furthermore, the maximum luminance reached 26.0 cd/m(2) at 61 V for 2.5-mu m-thick microfluidic OLED with PLQ, and the decreased EL luminance was recovered by replacing the degraded emitting layer with a fresh liquid emitter. We expect that on-demand multi-color EL emissions and refreshable luminance features of the proposed microfluidic OLEDs will be highly promising technologies for future long-life light-emitting device applications. (C) 2014 Elsevier B.V. All rights reserved.. |
| 887. | L. Zhao, T. Komino, M. Inoue, J. -H. Kim, J. C. Ribierre, C. Adachi, Horizontal molecular orientation in solution-processed organic light-emitting diodes, APPLIED PHYSICS LETTERS, 10.1063/1.4907890, 106, 6, 2015.02, Horizontal orientation of the emission transition dipole moments achieved in glassy vapor-deposited organic thin films leads to an enhancement of the light out-coupling efficiency in organic light-emitting diodes (OLEDs). Here, our combined study of variable angle spectroscopic ellipsometry and angle dependent photoluminescence demonstrates that such a horizontal orientation can be achieved in glassy spin-coated organic films based on a composite blend of a heptafluorene derivative as a dopant and a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl as a host. Solution-processed fluorescent OLEDs with horizontally oriented heptafluorene emitters were then fabricated and emitted deep blue electroluminescence with an external quantum efficiency as high as 5.3%. (C) 2015 AIP Publishing LLC.. |
| 888. | Takahiro Higuchi, Hajime Nakanotani, Chihaya Adachi, High-Efficiency White Organic Light-Emitting Diodes Based on a Blue Thermally Activated Delayed Fluorescent Emitter Combined with Green and Red Fluorescent Emitters, ADVANCED MATERIALS, 10.1002/adma.201404967, 27, 12, 2019-2023, 2015.03, A new device architecture for highly efficient white organic light-emitting diodes is proposed, using a molecule exhibiting blue thermally activated delayed fluorescence as a common source of singlet excitons for molecules emitting red and green light based on conventional fluorescence. The device, with an optimum combination of materials, shows a maximum external quantum efficiency of over 12% without using phosphorescent emitters.. |
| 889. | Qisheng Zhang, Daniel Tsang, Hirokazu Kuwabara, Yasuhiro Hatae, Bo Li, Takehiro Takahashi, Sae Youn Lee, Takuma Yasuda, Chihaya Adachi, Nearly 100% Internal Quantum Efficiency in Undoped Electroluminescent Devices Employing Pure Organic Emitters, ADVANCED MATERIALS, 10.1002/adma.201405474, 27, 12, 2096-2100, 2015.03, The design of efficient and concentration-insensitive metal-free thermally activateddelayed fluorescence (TADF) materials is reported. Blue and green organic light-emitting diodes (OLEDs) containing a hole-transport layer, an undoped TADF emissive layer, and an electron-transport layer achieve maximum external quantum efficiencies of 19%, which is comparable to the best doped OLEDs.. |
| 890. | Taro Furukawa, Hajime Nakanotani, Munetomo Inoue, Chihaya Adachi, Dual enhancement of electroluminescence efficiency and operational stability by rapid upconversion of triplet excitons in OLEDs, SCIENTIFIC REPORTS, 10.1038/srep08429, 5, 8429, 2015.02, Recently, triplet harvesting via a thermally activated delayed fluorescence (TADF) process has been established as a realistic route for obtaining ultimate internal electroluminescence (EL) quantum efficiency in organic light-emitting diodes (OLEDs). However, the possibility that the rather long transient lifetime of the triplet excited states would reduce operational stability due to an increased chance for unwarranted chemical reactions has been a concern. Herein, we demonstrate dual enhancement of EL efficiency and operational stability in OLEDs by employing a TADF molecule as an assistant dopant and a fluorescent molecule as an end emitter. The proper combination of assistant dopant and emitter molecules realized a "one-way'' rapid Forster energy transfer of singlet excitons from TADF molecules to fluorescent emitters, reducing the number of cycles of intersystem crossing (ISC) and reverse ISC in the TADF molecules and resulting in a significant enhancement of operational stability compared to OLEDs with a TADF molecule as the end emitter. In addition, we found that the presence of this rapid energy transfer significantly suppresses singlet-triplet annihilation. Using this finely-tuned rapid triplet-exciton upconversion scheme, OLED performance and lifetime was greatly improved.. |
| 891. | Atula S. D. Sandanayaka, Kou Yoshida, Toshinori Matsushima, Chihaya Adachi, Exciton Quenching Behavior of Thermally Activated Delayed Fluorescence Molecules by Charge Carriers, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/acs.jpcc.5b01314, 119, 14, 7631-7636, 2015.04, The quenching of singlet excitons by injected charge carriers in molecules that display thermally activated delayed fluorescence (TADF) was investigated using time-resolved transient photoluminescence (PL) techniques. Injected electrons did not affect the excitons; however, injected holes caused significant quenching. Using a rate-equation analysis, the hole-induced exciton quenching rate was determined to be between 10(-11) and 10(-12) cm(3) s(-1). Interestingly, the TADF emission component was enhanced in the presence of injected holes, plausibly due to a reduction of the singlet-exciton energy level.. |
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工学部・工学研究院
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