Article
Engineering, Chemical
Jeonghoon Han, Young-Su Ko, Youngsuk Nam, Choongyeop Lee
Summary: Recently, the thermal condition within the membrane has been explored as a means to enhance power generation in membrane-based energy harvesting from salinity difference. In this work, we experimentally demonstrate that even a negligibly small thermal gradient within a nanoporous membrane can significantly enhance osmotic power generation. Moreover, we propose that the direction of the imposed temperature difference can lead to up to 5.3 times power enhancement by influencing the effective ion concentration across the membrane.
JOURNAL OF MEMBRANE SCIENCE
(2023)
Article
Optics
Qi Zhu, Qingduo Duanmu
Summary: By investigating the influence of heavy atoms on the EL performance of OLEDs containing TADF materials, the study successfully enhanced device performance through optimization of doping concentration and thickness, resulting in a device with high current efficiency and external quantum efficiency at high brightness.
OPTICS COMMUNICATIONS
(2021)
Article
Chemistry, Multidisciplinary
Hao Gong, Heng Yu, Yang Zhang, Letong Feng, Yang Tian, Ganglong Cui, Hongbing Fu
Summary: Recently, researchers synthesized a nontoxic two-dimensional organic-inorganic metal hybrid halides (OIMHs) called PBA(2)[ZnX4], which exhibit stable long persistent luminescence (LPL) emission at room temperature and can be excited by low power sources. The LPL emission comes from the thermally activated charge separation state, and these materials have low cost and high stability.
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
(2023)
Article
Chemistry, Multidisciplinary
Kazuya Jinnai, Naohiro Nishimura, Chihaya Adachi, Ryota Kabe
Summary: The study investigated the charge carrier dynamics of a binary organic long-persistent luminescence system consisting of electron donors and acceptors, confirming the presence of thermal activation processes, thermally activated delayed fluorescence, and thermoluminescence in the system.
Article
Chemistry, Applied
Jihoon Kang, Ha Lim Lee, Junseop Lim, Jun Yeob Lee
Summary: In organic light-emitting diodes (OLEDs), host engineering is crucial for improving device performance. However, achieving high efficiency in blue phosphorescent OLEDs remains challenging due to the high triplet energy of blue phosphors. In this study, a thermally activated delayed fluorescence-type host with a sterically modulated carbazole-triazine backbone structure is developed. By incorporating a spatially twisted pi-spacer, the host exhibits a short delayed decay time and high triplet energy with a small singlet-triplet energy splitting. This photophysical modulation enables efficient utilization of triplet excitons, leading to significantly improved device performance with a maximum external quantum efficiency of 23.6%.
Article
Chemistry, Multidisciplinary
Xuan-Jun Chen, Yu-Ting Huang, Dian Luo, Chih-Hao Chang, Chin-Wei Lu, Hai-Ching Su
Summary: This work proposes novel white LECs based on phosphor-sensitized thermally activated delayed fluorescence (TADF), which have advantages of simple device architecture, low operation voltage, and insensitivity to the electrode work functions. The white LECs demonstrate efficient energy transfer efficiency and high device efficiency, with a high external quantum efficiency of 9.6%. By employing diffusive substrates to extract the light trapped in the substrate, the device efficiency can be further improved by approximately 50%. This work successfully demonstrates the potential of phosphor-sensitized TADF white LECs as efficient white light-emitting devices.
CHEMISTRY-A EUROPEAN JOURNAL
(2023)
Article
Chemistry, Multidisciplinary
Peng-Yan Fu, Bao-Ning Li, Qiang-Sheng Zhang, Jun-Ting Mo, Shi-Cheng Wang, Mei Pan, Cheng-Yong Su
Summary: In this study, a coordination polymer with ESIPT properties was synthesized, and the switching between thermally activated fluorescence and long persistent luminescence was achieved by controlling the temperature. The mechanism of ISC/RISC energy transfer in the coordination polymer was revealed, providing a new pathway for the design and application of advanced optical materials in the future.
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
(2022)
Article
Energy & Fuels
Mona A. Abdel-Mawla, Muhammed A. Hassan, Adel Khalil
Summary: This study is the first attempt to parametrically optimize the PCM-TABS system integration in radiant cooling systems, demonstrating significant energy and cost savings with the use of PCMs in TABS, especially when incorporated into radiant ceilings.
JOURNAL OF ENERGY STORAGE
(2022)
Review
Materials Science, Multidisciplinary
Jixin Jiang, Jun Yeob Lee
Summary: Phosphorescent and TADF OLEDs have short lifetimes despite high efficiencies. This study compares the degradation processes of phosphorescent and TADF OLEDs, highlighting the importance of material and device stability in addressing degradation.
Article
Chemistry, Organic
Sheng-Nan Zou, Chen-Chen Peng, Sheng-Yi Yang, Yang-Kun Qu, You-Jun Yu, Xing Chen, Zuo-Quan Jiang, Liang-Sheng Liao
Summary: Three emissive bridged-triphenylamine derivatives incorporating carbon, oxygen, and sulfur atoms with two carbonyl groups exhibit potential as narrowband thermally activated delayed fluorescence emitters. Organic light-emitting diodes based on these derivatives achieve high external quantum efficiencies for blue, green, and yellow emissions.
Article
Materials Science, Multidisciplinary
Jixin Jiang, Ho Jin Jang, Kyung Hyung Lee, Junseop Lim, Jae-Min Kim, Suling Zhao, Jun Yeob Lee
Summary: This study investigates the degradation mechanisms of triplet exciton harvesting OLEDs and finds that different emitters cause different degradation issues under different mechanisms, providing important guidance for improving the stability of OLEDs.
ADVANCED OPTICAL MATERIALS
(2023)
Article
Chemistry, Physical
Leonardo Evaristo de Sousa, Piotr de Silva
Summary: This study develops a diabatization procedure to investigate TADF molecules. By analyzing the diabatic Hamiltonian of the molecules, we provide physical interpretations related to electronic states and molecular geometries. The study also finds the influence of vibrations on TADF efficiency and proposes different optimization strategies.
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
(2022)
Article
Materials Science, Multidisciplinary
Bangjin Sun, Kai-Ning Tong, Xing Chen, Jian-Li He, Han Liu, Man-Keung Fung, Jian Fan
Summary: The study introduced a triazine-carbazole hybrid (Trz-PhCz) with a short triplet lifetime, achieving extremely low efficiency roll-offs in green, yellow, orange, and red OLEDs. The optimized orange device showed a record-high maximum EQE of 31.4% and 25.5% at 10,000 cd m^-2. Additionally, high PE(max)s were obtained for Ir(ppy)2(acac) and PO-01-based devices, with a white OLED based on Trz-PhCz exhibiting a remarkable PEmax of 102.5 lm W^-1 with a CIE of (0.42, 0.48).
JOURNAL OF MATERIALS CHEMISTRY C
(2021)
Article
Optics
Qi Zhu, Qingduo Duanmu
Summary: In this study, the iridium (III)bis[4-(tert-butyl)-2,6-diuoro-2,3-bipyridine]acetylacetonate (FK306) doped layer was utilized as an electron-transport layer to optimize the electron density and improve the electroluminescent performance of yellow TADF devices. With a suitable device design strategy, significant improvements in efficiency were achieved while reducing efficiency roll-off.
Article
Chemistry, Multidisciplinary
Chunbo Duan, Chunmiao Han, Jing Zhang, Xianfa Zhang, Chaochao Fan, Hui Xu
Summary: This study explores the external enhancement effects of exciplex matrixes on TADF emitters, achieving significantly improved efficiency and performance. The exciplex matrixes not only enhance the reverse intersystem crossing efficiency for TADF facilitation, but also support charge preseparation for efficient energy transfer and effective quenching suppression, leading to state-of-the-art EL performances in yellow TADF diodes.
ADVANCED FUNCTIONAL MATERIALS
(2021)
Article
Chemistry, Physical
Tomonori Nakamura, Martin Vacha
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2020)
Article
Optics
Dharmendar Kumar Sharma, Shuzo Hirata, Martin Vacha
JOURNAL OF LUMINESCENCE
(2020)
Article
Chemistry, Multidisciplinary
Tzu-Wei Tseng, Hao Yan, Tomonori Nakamura, Shun Omagari, Ji-Seon Kim, Martin Vacha
Article
Materials Science, Multidisciplinary
Keisuke Ueda, Miho Aizawa, Atsushi Shishido, Martin Vacha
Summary: Single-particle fluorescence imaging is employed to monitor dynamic processes during patterned photopolymerization of liquid-crystalline monomers, revealing the effects of spatial gradient of chemical potential on mutual diffusion of polymers and monomers, as well as flow-induced orientation of the polymers under structured illumination.
NPG ASIA MATERIALS
(2021)
Article
Chemistry, Multidisciplinary
Ryotaro Furuya, Shun Omagari, Qiwen Tan, Heiko Lokstein, Martin Vacha
Summary: By combining conductive atomic force microscopy (AFM) and confocal fluorescence microscopy, researchers measured photocurrents passing through single trimeric photosystem I (PSI) complexes near single gold nanorods (AuNRs). The study revealed that localized plasmons can enhance photocurrents and provided deeper insight into molecular mechanisms of plasmon-enhanced phenomena.
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
(2021)
Article
Chemistry, Multidisciplinary
Yuma Goto, Shun Omagari, Ryuma Sato, Takuya Yamakado, Ryo Achiwa, Nilanjan Dey, Kensuke Suga, Martin Vacha, Shohei Saito
Summary: The study utilized a dual fluorescent molecular probe to monitor nanoscale dynamics in polystyrenes, revealing that planarization of the molecule in the excited state only occurs when a large polymer free volume is available nearby, lasting on average 1.2 seconds. This investigation provides insights into the dynamics of molecular environments through statistical analysis and computational simulations.
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
(2021)
Article
Chemistry, Physical
Hao Yan, Tzu-Wei Tseng, Shun Omagari, Iain Hamilton, Tomonori Nakamura, Martin Vacha, Ji-Seon Kim
Summary: In this study, the role of the beta-phase in polyfluorene-based copolymers on energy transfer (ET) was investigated. The results showed that the beta-phase can significantly improve the performance and color purity of polymer light-emitting devices. By conducting single-molecule spectroscopy, it was found that efficient ET occurs from the glassy phase to the beta-phase. Density functional theory calculations and temperature-dependent spectroscopy confirmed the mechanism of ET from the glassy phase to the CT state.
JOURNAL OF CHEMICAL PHYSICS
(2022)
Article
Chemistry, Physical
Anubha Agarwal, Shun Omagari, Martin Vacha
Summary: Perovskite solar cells have achieved significant technological progress, but understanding the fundamental photophysical properties of perovskite materials is equally important. This study utilizes fluorescence microscopy to investigate the nanoscale properties of mixed-cation perovskite films. The results reveal compositional heterogeneity and photoluminescence intensity fluctuations in the films.
ACS ENERGY LETTERS
(2022)
Article
Chemistry, Multidisciplinary
Tomonori Nakamura, Shun Omagari, Xiaobin Liang, Qiwen Tan, Ken Nakajima, Martin Vacha
Summary: Using atomic force microscopy and fluorescence microscopy, we studied the single-chain structure of conjugated polymer polyfluorene (PFO). We found that mechanical stretching of the chain causes disappearance of the green emission band, indicating that the green emission originates from an intrachain aggregated state on the self-folded chain. Additionally, stretching upon laser irradiation leads to the appearance of additional features in the force spectra, small force peales in the initial stages of the unfolding, which are attributed to a combination of excitonic and van der Waals coupling of a ground-state intrachain aggregate.
Article
Materials Science, Multidisciplinary
Xiayan Wu, Shun Omagari, Jinwei Gao, Martin Vacha
Summary: Studied CsPbX3-MOF composites based on twinned Pb-X-based MOFs to investigate the crystallization kinetics and photoluminescence (PL) properties. Found a large compositional heterogeneity in the embedded mixed halogen perovskites, which is a dynamic phenomenon with spectral fluctuations of individual nanocrystals on the time scales of tens of seconds under excitation. In addition, compositional changes correlated over distances of micrometers indicate collective ionic diffusion in the system. In situ PL spectroscopy provides unique insights into the fundamental photophysical properties and feedback for further development and potential applications of perovskite-MOF composites.
ADVANCED OPTICAL MATERIALS
(2023)
Article
Chemistry, Physical
Toranosuke Takagi, Shun Omagari, Martin Vacha
Summary: In this study, ligand exchange on the CsPbBr3 perovskite nanocrystal surface was performed and its effect on photoluminescence blinking was investigated. By replacing oleic acid and oleylamine ligands with quaternary amine ligands used in the synthesis process, a substantial increase in photoluminescence quantum yield and improved blinking characteristics were achieved. Statistical analysis showed longer duration of ON-times, shorter OFF-times, and a higher fraction of ON-time intervals after the ligand exchange.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2023)
Article
Chemistry, Multidisciplinary
Anubha Agarwal, Shun Omagari, Martin Vacha
Summary: We prepared and characterized mixed cation perovskite films of MA(1-x)FA(x)PbI(3) composition with x = 0, 0.3, and 0.5 at the nanoscale level. Films with x = 0.5 and 0.3, prepared using ethyl acetate as an antisolvent in a one-step spin-coating process, showed compositionally stability in ambient air for over a year, unlike films prepared with chlorobenzene antisolvent. In situ photoluminescence spectroscopy was used to monitor the degradation onset near the film edges, with degradation products exhibiting similar photoluminescence spectra to 2D perovskite sheets. Morphologically, aging of the films resulted in the coalescence of film grain structure into larger crystal grains. Additionally, aging did not affect dynamic photoluminescence quenching or long-range charge diffusion on the order of micrometers.
Article
Chemistry, Physical
Anubha Agarwal, Shun Omagari, Martin Vacha
Summary: Perovskite solar cells have shown great progress, but understanding the fundamental photophysical properties is equally important. Using fluorescence microscopy, we observed compositional heterogeneity and dynamic nonradiative quenching in mixed-cation perovskite films. The films with 50% FA fraction showed the highest intensity and least quenching, indicating the presence of truly mixed MA/FA domains. Additionally, the correlation in blinking between locations suggests transparent grain boundaries for efficient charge migration.
ACS ENERGY LETTERS
(2022)
Article
Chemistry, Multidisciplinary
Jeladhara Sobhanan, Philip Jones, Reiko Kohara, Sakiko Sugino, Martin Vacha, Challapally Subrahmanyam, Yuta Takano, Fred Lacy, Vasudevanpillai Biju
Article
Chemistry, Physical
Shun Omagari, Martin Vacha
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2020)
