Journal
JOURNAL OF THE CHINESE CHEMICAL SOCIETY
Volume 69, Issue 8, Pages 1485-1494Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/jccs.202200094
Keywords
deep-red fluorescence emitter; diphenylphosphine oxide; exciplex; organic light-emitting diode; thermally-activated delayed fluorescence; triazatruxene
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Funding
- Ministry of Science and Technology [MOST106-2112-M-019-002-MY3, MOST110-2113-M-002-021, MOST 107-2113-M-002-019-MY3]
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In this study, a new triazatruxene-based donor was introduced to suppress aggregation. The effects of steric hindrance on exciplex formation were investigated. By selecting appropriate exciplex-forming blends as the emitting layer, efficient OLED devices were achieved.
In this study, a new triazatruxene-based donor Tr-iBu bearing branched alkyl groups is reported to suppress the aggregation found in a previously reported methyl-substituted counterpart Tr-Me. The effects of a steric factor on the propensity of exciplex formation were examined by respectively mixing these triazatruxene-based donors with PO-T2T and two new acceptors PO-T2P and PO-Pyr, all bearing phosphine oxide as the peripheral groups and N-heteroarene cores with different numbers of nitrogen. Based on the steric hindrance of side groups and their corresponding molecular orbitals alignments of donors and acceptors, the characteristics of exciplex-forming systems were analyzed. Among them, the exciplex-forming blends Tr-iBu:PO-T2P and Tr-iBu:PO-Pyr were selected to serve as the emitting layer (EML) to achieve OLED devices with a moderate maximum external quantum efficiency (EQE(max)) of 8.27 and 7.54%, respectively. Adopting the Forster resonance energy transfer strategy, the exciplex cohost was doped with a fluorescence emitter, DPy2CN, to realize a deep-red OLED device with the emission peak centered at 674 nm while retaining EQE(max) of 6.28%. Our results highlight the importance of suppressing the donor aggregation, adequate donor: acceptor combination, and a suitable triplet state of composing the materials for giving efficient exciplex-based OLEDs.
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