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Enhanced Electroluminescence Efficiency Using Reverse Intersystem Crossing Induced by the Strong Triplet Fusion of Rubrene as a Sensitizer

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journal contribution
posted on 21.04.2020 by Fenlan Qu, Weiyao Jia, Hongqiang Zhu, Xiantong Tang, Jing Xu, Xi Zhao, Caihong Ma, Shengnan Ye, Zuhong Xiong
The sensitization properties of rubrene with strong triplet fusion (TF) and the physical mechanisms of the enhanced electroluminescence efficiency were studied from a series of rubrene–DCJTB–codoped OLEDs. Although they have the same electroluminescence spectra, the target device containing rubrene as a sensitizer (mCP/5% rubrene/5% DCJTB) was more efficient than the reference device (mCP/5ÜJTB). This is because in the target device, besides the direct charge injection (DCI) onto DCJTB dopant, there exists reverse intersystem crossing (RISC) of triplet excitons via strong TF of rubrene and the following multiple energy-transfer channels sensitized by rubrene. Importantly, the EL was stronger from rubrene sensitization than from the DCI of DCJTB. Moreover, both the EL efficiency and the sensitization channel were enhanced at high sensitizer concentration, large bias current, and low operating temperature. These findings demonstrate that traditional fluorescent rubrene can be used as an effective sensitizer to realize high-performance OLEDs.