The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Xiaohong Zhang - One of the best experts on this subject based on the ideXlab platform.
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novel strategy to develop Exciplex emitters for high performance oleds by employing thermally activated delayed fluorescence materials
Advanced Functional Materials, 2016Co-Authors: Jiaxiong Chen, Caijun Zheng, Fan Li, Xuemei Ou, Xiaohong Zhang, Kai Wang, Dongyang Chen, Yuping DongAbstract:To develop high-performance thermally activated delayed fluorescence (TADF) Exciplex emitters, a novel strategy of introducing a single-molecule TADF emitter as one of the constituting materials has been presented. Such a new type of Exciplex TADF emitter will have two reverse intersystem crossing (RISC) routes on both the pristine TADF molecules and the Exciplex emitters, benefiting the utilization of triplet excitons. Based on a newly designed and synthesized single-molecule TADF emitter MAC, a highly efficient Exciplex emitter MAC:PO-T2T has been obtained. The device based on MAC:PO-T2T with a weight ratio of 7:3 exhibits a low turn-on voltage of 2.4 V, high maximum efficiency of 52.1 cd A−1 (current efficiency), 45.5 lm W−1 (power efficiency), and 17.8% (external quantum efficiency, EQE), as well as a high EQE of 12.3% at a luminance of 1000 cd m−2. The device shows the best performance among reported organic light-emitting devices based on Exciplex emitters. Such high-efficiency and low-efficiency roll-off should be ascribed to the additional reverse intersystem crossing process on the MAC molecules, showing the advantages of the strategy described in this study.
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prediction and design of efficient Exciplex emitters for high efficiency thermally activated delayed fluorescence organic light emitting diodes
Advanced Materials, 2015Co-Authors: Zhan Chen, Caijun Zheng, Fan Li, Xuemei Ou, Xiaohong ZhangAbstract:: High-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes based on Exciplex emitters are demonstrated. The best device, based on a TAPC:DPTPCz emitter, shows a high external quantum efficiency of 15.4%. Strategies for predicting and designing efficient Exciplex emitters are also provided. This approach allow prediction and design of efficient Exciplex emitters for achieving high-efficiency organic light-emitting diodes, for future use in displays and lighting applications.
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nearly 100 triplet harvesting in conventional fluorescent dopant based organic light emitting devices through energy transfer from Exciplex
Advanced Materials, 2015Co-Authors: Zhan Chen, Caijun Zheng, Miao Chen, Xiaohong ZhangAbstract:: Nearly 100% triplet harvesting in conventional fluorophor-based organic light-emitting devices is realized through energy transfer from Exciplex. The best C545T-doped device using the Exciplex host exhibits a maximum current efficiency of 44.0 cd A(-1) , a maximum power efficiency of 46.1 lm W(-1) , and a maximum external quantum efficiency of 14.5%.
Ken-tsung Wong - One of the best experts on this subject based on the ideXlab platform.
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High Efficiency Exciplex-based OLEDs (Conference Presentation)
Organic and Hybrid Light Emitting Materials and Devices XXIII, 2019Co-Authors: Ken-tsung WongAbstract:Organic materials that exhibit thermally activated delayed fluorescence (TADF) are attractive materials for realizing high efficiency OLEDs. A tremendous amount of tailor-made TADF molecules have been reported based on the manipulation of the intramolecular charge transfer as well as the HOMO-LUMO overlap. Beyond this strategy, there is an emerging approach of using Exciplex that simply involves intermolecular charge transfer between physically blended electron donor and acceptor molecules. This is because the Exciplex-based systems can realize relatively small ΔEST since the electron and hole are located on two different molecules, thereby giving small exchange energy. Consequently, Exciplex-based OLEDs have the possibility to maximize the TADF contribution and achieve theoretical 100% internal quantum efficiency. However, research on Exciplex-forming materials is still at a growing stage, and consequently, new molecules with remarkable electro and/or photo-physical property are still being explored. Thus, the developments of Exciplex-forming systems for achieving high-efficiency and high stability OLED devices are prospective. In this conference, our updated results of new efficient Exciplex systems, and Exciplex-hosted fluorescent and phosphorescent OLEDs with high efficiency and high stability will be reported.
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High efficiency OLEDs based on Exciplex (Conference Presentation)
Organic Light Emitting Materials and Devices XXII, 2018Co-Authors: Ken-tsung WongAbstract:Organic materials that display thermally activated delayed fluorescence (TADF) are a striking class of functional materials that have witnessed a booming progress in recent years. The small ΔEST in TADF-based systems prompts highly efficient RISC from T1 to S1 states, and consequently both singlet and triplet excitons can be harvested for light emission. For the last five years, a tremendous amount of TADF molecules have been reported based on the manipulation of the intramolecular charge transfer as well as the HOMO-LUMO overlap. Beyond this strategy, there is an emerging approach that simply involves intermolecular charge transfer between physically blended electron donor and acceptor molecules for high efficiency TADF-based OLEDs (via Exciplex formation). This is because the Exciplex-based systems can realize relatively small ΔEST (0–0.05 eV) much more easily since the electron and hole are positioned on two different molecules, thereby giving small exchange energy. Consequently, Exciplex-based OLEDs have the possibility to maximize the TADF contribution and achieve theoretical 100% internal quantum efficiency and solve the challenging issue of achieving small ΔEST in organic systems. However, research on Exciplex-forming materials is still at a growing stage, and consequently, new molecules with remarkable electro and or photo-physical property are still being explored. Thus, by focusing on the development of Exciplex systems, we shall have the prospective of achieving the demands for high-efficiency and high stability OLED devices. In this conference, we will report our updated results of new efficient Exciplex systems, and Exciplex-hosted fluorescent and phosphorescent OLEDs with high efficiency and high stability.
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probe Exciplex structure of highly efficient thermally activated delayed fluorescence organic light emitting diodes
Nature Communications, 2018Co-Authors: Monima Sarma, Ken-tsung Wong, Wenyi Hung, Yiting Chen, Pinyi Chiang, Weitsung Chuang, Weichieh Tang, Pitai ChouAbstract:The lack of structural information impeded the access of efficient luminescence for the Exciplex type thermally activated delayed fluorescence (TADF). We report here the pump-probe Step-Scan Fourier transform infrared spectra of Exciplex composed of a carbazole-based electron donor (CN-Cz2) and 1,3,5-triazine-based electron acceptor (PO-T2T) codeposited as the solid film that gives intermolecular charge transfer (CT), TADF, and record-high Exciplex type cyan organic light emitting diodes (external quantum efficiency: 16%). The transient infrared spectral assignment to the CT state is unambiguous due to its distinction from the local excited state of either the donor or the acceptor chromophore. Importantly, a broad absorption band centered at ~2060 cm−1 was observed and assigned to a polaron-pair absorption. Time-resolved kinetics lead us to conclude that CT excited states relax to a ground-state intermediate with a time constant of ~3 µs, followed by a structural relaxation to the original CN-Cz2:PO-T2T configuration within ~14 µs. The development of Exciplex-type hosts for thermally activated delayed fluorescence organic light-emitting diodes is hindered by a lack of structural information for these donor:acceptor blends. Here, the authors report the pump-probe Step-Scan Fourier transform IR spectra for a D:A Exciplex host.
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remote steric effect as a facile strategy for improving the efficiency of Exciplex based oleds
ACS Applied Materials & Interfaces, 2017Co-Authors: Wenyi Hung, Pinyi Chiang, Tingchih Wang, Boji Peng, Ken-tsung WongAbstract:This work reports a new strategy of introducing remote steric effect onto the electron donor for giving the better performance of the Exciplex-based organic light-emitting device (OLED). The bulky triphenylsilyl group (SiPh3) was introduced onto the fluorene bridge of 4,4′-(9H-fluorene-9,9-diyl)bis(N,N-di-p-tolylaniline) (DTAF) to create remote steric interactions for increasing the possibility of effective contacts between electron-donating chromophores and acceptor molecules, rendering the resulting Exciplex to have a higher photoluminescence quantum yield (PLQY). The green Exciplex device based on DSDTAF:3N-T2T (1:1) as an emitting layer exhibits a low turn-on voltage of 2.0 V, high maximum efficiencies (13.2%, 42.9 cd A–1, 45.5 lm W–1), which are higher than the device employed DTAF (without SiPh3 groups) (11.6%, 35.3 cd A–1, 41.3 lm W–1) as donor under the same device structure. This strategy was further examined for blue Exciplex, where the EQE was enhanced from 9.5% to 12.5% as the electron accepto...
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the first tandem all Exciplex based woled
Scientific Reports, 2015Co-Authors: Wenyi Hung, Ken-tsung Wong, Guancheng Fang, Shuohsien Cheng, Pitai ChouAbstract:Exploiting our recently developed bilayer interface methodology, together with a new wide energy-gap, low LUMO acceptor (A) and the designated donor (D) layers, we succeeded in fabricating an Exciplex-based organic light-emitting diode (OLED) systematically tuned from blue to red. Further optimization rendered a record-high blue Exciplex OLED with ηext of 8%. We then constructed a device structure configured by two parallel blend layers of mCP/PO-T2T and DTAF/PO-T2T, generating blue and yellow Exciplex emission, respectively. The resulting device demonstrates for the first time a tandem, all-Exciplex-based white-light OLED (WOLED) with excellent efficiencies ηext: 11.6%, ηc: 27.7 cd A−1, and ηp: 15.8 ml W−1 with CIE(0.29, 0.35) and CRI 70.6 that are nearly independent of EL intensity. The tandem architecture and blend-layer D/A (1:1) configuration are two key elements that fully utilize the Exciplex delay fluorescence, providing a paragon for the use of low-cost, abundant organic compounds en route to commercial WOLEDs.
Pitai Chou - One of the best experts on this subject based on the ideXlab platform.
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probe Exciplex structure of highly efficient thermally activated delayed fluorescence organic light emitting diodes
Nature Communications, 2018Co-Authors: Monima Sarma, Ken-tsung Wong, Wenyi Hung, Yiting Chen, Pinyi Chiang, Weitsung Chuang, Weichieh Tang, Pitai ChouAbstract:The lack of structural information impeded the access of efficient luminescence for the Exciplex type thermally activated delayed fluorescence (TADF). We report here the pump-probe Step-Scan Fourier transform infrared spectra of Exciplex composed of a carbazole-based electron donor (CN-Cz2) and 1,3,5-triazine-based electron acceptor (PO-T2T) codeposited as the solid film that gives intermolecular charge transfer (CT), TADF, and record-high Exciplex type cyan organic light emitting diodes (external quantum efficiency: 16%). The transient infrared spectral assignment to the CT state is unambiguous due to its distinction from the local excited state of either the donor or the acceptor chromophore. Importantly, a broad absorption band centered at ~2060 cm−1 was observed and assigned to a polaron-pair absorption. Time-resolved kinetics lead us to conclude that CT excited states relax to a ground-state intermediate with a time constant of ~3 µs, followed by a structural relaxation to the original CN-Cz2:PO-T2T configuration within ~14 µs. The development of Exciplex-type hosts for thermally activated delayed fluorescence organic light-emitting diodes is hindered by a lack of structural information for these donor:acceptor blends. Here, the authors report the pump-probe Step-Scan Fourier transform IR spectra for a D:A Exciplex host.
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the first tandem all Exciplex based woled
Scientific Reports, 2015Co-Authors: Wenyi Hung, Ken-tsung Wong, Guancheng Fang, Shuohsien Cheng, Pitai ChouAbstract:Exploiting our recently developed bilayer interface methodology, together with a new wide energy-gap, low LUMO acceptor (A) and the designated donor (D) layers, we succeeded in fabricating an Exciplex-based organic light-emitting diode (OLED) systematically tuned from blue to red. Further optimization rendered a record-high blue Exciplex OLED with ηext of 8%. We then constructed a device structure configured by two parallel blend layers of mCP/PO-T2T and DTAF/PO-T2T, generating blue and yellow Exciplex emission, respectively. The resulting device demonstrates for the first time a tandem, all-Exciplex-based white-light OLED (WOLED) with excellent efficiencies ηext: 11.6%, ηc: 27.7 cd A−1, and ηp: 15.8 ml W−1 with CIE(0.29, 0.35) and CRI 70.6 that are nearly independent of EL intensity. The tandem architecture and blend-layer D/A (1:1) configuration are two key elements that fully utilize the Exciplex delay fluorescence, providing a paragon for the use of low-cost, abundant organic compounds en route to commercial WOLEDs.
Wenlian Li - One of the best experts on this subject based on the ideXlab platform.
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the application of charge transfer host based Exciplex and thermally activated delayed fluorescence materials in organic light emitting diodes
Organic Electronics, 2019Co-Authors: Ziqi Wang, Bo Zhao, Chao Wang, Heng Zhang, Wenlian LiAbstract:Abstract Here, we review systematically the applications of Exciplex and thermally activated delayed fluorescence (TADF) materials as the host in organic light-emitting diodes (OLEDs), who is the charge transfer host based inter-molecular and intra-molecular, respectively. Exciplex and TADF materials present many advantages of natural bipolarity, small singlet-triplet splitting energy and low driving voltage to act as the host rather than emitter. The applications of Exciplex and TADF materials as the host in phosphorescent, fluorescent and white OLEDs are given and new challenges, suggestions are also provided finally for further research and potential development of this area.
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efficient Exciplex emission from intramolecular charge transfer material
Organic Electronics, 2015Co-Authors: Tianyou Zhang, Bo Zhao, Wenlian Li, Zisheng Su, Hairuo WuAbstract:Abstract New Exciplexes formed between a typical intramolecular charge transfer (ICT) material (bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS)) and a series of electron donor and acceptors in donor:acceptor system have been systematically demonstrated. It is found that such ICT materials could form Exciplex with both standalone electron donor and acceptor materials with itself as acceptor and donor components, which is based on the presence of both donor and acceptor species in the ICT material. The emission spectra of Exciplex OLEDs based on ICT materials could be regularly tuned ranging from blue to yellow color by changing energy level alignment between ICT and standalone donor/acceptor materials. Among these Exciplexes, DMAC-DPS:PO-T2T combination offered the highest Exciplex EL performance, with its peak external quantum efficiency, luminance and current efficiency of 9.08%, 35,000 cd/m2 and 30 cd/A, respectively. On the other hand, we also found that the Exciplex efficiency was insensitive with the weight ratio between ICT material and acceptor, which means ‘doping’ of ICT material into the acceptor. Our finding extend the usage and selection scope of the TADF material.
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simple structured hybrid woleds based on incomplete energy transfer mechanism from blue Exciplex to orange dopant
Scientific Reports, 2015Co-Authors: Tianyou Zhang, Bo Zhao, Wenlian Li, Zisheng Su, Hairuo WuAbstract:Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, Exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet Exciplex to both singlet Exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue Exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both Exciplex-fluorescence and Exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.
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efficient triplet application in Exciplex delayed fluorescence oleds using a reverse intersystem crossing mechanism based on a δes t of around zero
ACS Applied Materials & Interfaces, 2014Co-Authors: Tianyou Zhang, Bo Zhao, Wenlian Li, Zisheng Su, Hairuo Wu, Qi Ming Peng, Feng Zhang, Junbo WangAbstract:We demonstrate highly efficient Exciplex delayed-fluorescence organic light-emitting diodes (OLEDs) in which 4,4',4 ''-tris[3-methylphenyl(phenyl)-aminotriphenylamine (m-MTDATA) and 4,7-diphenyl-1,10-phenanthroline (Bphen) were selected as donor and acceptor components, respectively. Our m-MTDATA:Bphen Exciplex electroluminescence (EL) mechanism is based on reverse intersystem crossing (RISC) from the triplet to singlet excited states. As a result, an external quantum efficiency (EQE) of 7.79% at 10 mA/cm(2) was observed, which increases by 3.2 and 1.5 times over that reported in Nat. Photonics 2012, 6, 253 and Appl. Phys. Lett. 2012, 101, 023306, respectively. The high EQE would be attributed to a very easy RISC process because the energy difference between the singlet and triplet excited states is almost around zero. The verdict was proven by photoluminescence (PL) rate analysis at different temperatures and time-resolved spectral analysis. Besides, the study of the transient PL process indicates that the presence of an unbalanced charge in Exciplex EL devices is responsible for the low EQE and high-efficiency roll-off. When the Exciplex devices were placed in a 100 mT magnetic field, the permanently positive magnetoelectroluminescence and magnetoconductivity were observed. The magnetic properties confirm that the efficient Exciplex EL only originates from delayed fluorescence via RISC processes but is not related to the triplet-triplet annihilation process.
Wenyi Hung - One of the best experts on this subject based on the ideXlab platform.
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probe Exciplex structure of highly efficient thermally activated delayed fluorescence organic light emitting diodes
Nature Communications, 2018Co-Authors: Monima Sarma, Ken-tsung Wong, Wenyi Hung, Yiting Chen, Pinyi Chiang, Weitsung Chuang, Weichieh Tang, Pitai ChouAbstract:The lack of structural information impeded the access of efficient luminescence for the Exciplex type thermally activated delayed fluorescence (TADF). We report here the pump-probe Step-Scan Fourier transform infrared spectra of Exciplex composed of a carbazole-based electron donor (CN-Cz2) and 1,3,5-triazine-based electron acceptor (PO-T2T) codeposited as the solid film that gives intermolecular charge transfer (CT), TADF, and record-high Exciplex type cyan organic light emitting diodes (external quantum efficiency: 16%). The transient infrared spectral assignment to the CT state is unambiguous due to its distinction from the local excited state of either the donor or the acceptor chromophore. Importantly, a broad absorption band centered at ~2060 cm−1 was observed and assigned to a polaron-pair absorption. Time-resolved kinetics lead us to conclude that CT excited states relax to a ground-state intermediate with a time constant of ~3 µs, followed by a structural relaxation to the original CN-Cz2:PO-T2T configuration within ~14 µs. The development of Exciplex-type hosts for thermally activated delayed fluorescence organic light-emitting diodes is hindered by a lack of structural information for these donor:acceptor blends. Here, the authors report the pump-probe Step-Scan Fourier transform IR spectra for a D:A Exciplex host.
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Tandem red PhOLEDs based on Exciplex-forming co-host
2017 24th International Workshop on Active-Matrix Flatpanel Displays and Devices (AM-FPD), 2017Co-Authors: Wenyi HungAbstract:Exciplex forming cohosts have been widely adopted in phosphorescent organic light-emitting diodes (PHOLEDs), achieving high efficiency with low roll-off and low driving voltage. We employed a new Exciplex forming cohost composed of TAPC and CN-T2T as charge-transporting and emitting materials. The tandem red-emitting PhOLEDs using the Exciplex forming cohost achieved a maximum external quantum efficiency (EQE) of 40.6 % and power efficiency of 38.9 lm W-1 with low operating voltages and low efficiency roll-offs.
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remote steric effect as a facile strategy for improving the efficiency of Exciplex based oleds
ACS Applied Materials & Interfaces, 2017Co-Authors: Wenyi Hung, Pinyi Chiang, Tingchih Wang, Boji Peng, Ken-tsung WongAbstract:This work reports a new strategy of introducing remote steric effect onto the electron donor for giving the better performance of the Exciplex-based organic light-emitting device (OLED). The bulky triphenylsilyl group (SiPh3) was introduced onto the fluorene bridge of 4,4′-(9H-fluorene-9,9-diyl)bis(N,N-di-p-tolylaniline) (DTAF) to create remote steric interactions for increasing the possibility of effective contacts between electron-donating chromophores and acceptor molecules, rendering the resulting Exciplex to have a higher photoluminescence quantum yield (PLQY). The green Exciplex device based on DSDTAF:3N-T2T (1:1) as an emitting layer exhibits a low turn-on voltage of 2.0 V, high maximum efficiencies (13.2%, 42.9 cd A–1, 45.5 lm W–1), which are higher than the device employed DTAF (without SiPh3 groups) (11.6%, 35.3 cd A–1, 41.3 lm W–1) as donor under the same device structure. This strategy was further examined for blue Exciplex, where the EQE was enhanced from 9.5% to 12.5% as the electron accepto...
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the first tandem all Exciplex based woled
Scientific Reports, 2015Co-Authors: Wenyi Hung, Ken-tsung Wong, Guancheng Fang, Shuohsien Cheng, Pitai ChouAbstract:Exploiting our recently developed bilayer interface methodology, together with a new wide energy-gap, low LUMO acceptor (A) and the designated donor (D) layers, we succeeded in fabricating an Exciplex-based organic light-emitting diode (OLED) systematically tuned from blue to red. Further optimization rendered a record-high blue Exciplex OLED with ηext of 8%. We then constructed a device structure configured by two parallel blend layers of mCP/PO-T2T and DTAF/PO-T2T, generating blue and yellow Exciplex emission, respectively. The resulting device demonstrates for the first time a tandem, all-Exciplex-based white-light OLED (WOLED) with excellent efficiencies ηext: 11.6%, ηc: 27.7 cd A−1, and ηp: 15.8 ml W−1 with CIE(0.29, 0.35) and CRI 70.6 that are nearly independent of EL intensity. The tandem architecture and blend-layer D/A (1:1) configuration are two key elements that fully utilize the Exciplex delay fluorescence, providing a paragon for the use of low-cost, abundant organic compounds en route to commercial WOLEDs.
