Molecular engineering on all ortho-linked carbazole/oxadiazole hybrids toward highly-efficient thermally activated delayed fluorescence materials in OLEDs |
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| Institution: | 1. Key Lab for Flexible Electronics & Institute of Advanced Materials (IAM), Nanjing Tech University, Nanjing 211816, China;2. Department of Physics, Center for Optoelectronics Engineering Research, Yunnan University, Kunming 650091, China;3. Shaanxi Institute of Flexible Electronics (SIFE), North western Polytechnical University (NPU), Xi''an 710072, China;1. Department of Polymer Science and Engineering, Dankook University, 126, Jukjeon-dong, Suji-gu, Yongin, Gyeonggi, 448-701, Republic of Korea;2. School of Chemical Engineering, Sungkyunkwan University, 2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi, 440-746, Republic of Korea |
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| Abstract: | The highest efficiency thermally activated delayed fluorescence (TADF) emitters in OLEDs are mostly based on twisted donor/acceptor (D/A) type organic molecules. Herein, we report the rational molecular design on twisted all ortho-linked carbazole/oxadiazole (Cz/OXD) hybrids with tunable D-A interactions by adjusting the numbers of donor/acceptor units and electron-donating abilities. Singlet-triplet energy bandgaps (ΔEST) are facilely tuned from ∼0.4, 0.15 to ∼0 eV in D-A, D-A-D to A-D-A type compounds. This variation correlates well with triplet-excited-state frontier orbital spatial separation efficiency. Non-TADF feature with solid state photoluminescence quantum yield (PLQY) < 10% is observed in D-A type 2CzOXD and D-A-D type 4CzOXD. Owing to the extremely low ΔEST for efficient reverse intersystem crossing, strong TADF with PLQY of 71%–92% is achieved in A-D-A type 4CzDOXD and 4tCzDOXD. High external quantum efficiency from 19.4% to 22.6% is achieved in A-D-A typed 4CzDOXD and 4tCzDOXD. |
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| Keywords: | Oxadiazole Carbazole Donor-acceptor Organic light-emitting diodes Thermally activated delayed fluorescence |
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