Managing Locally Excited and Charge-Transfer Triplet States to Facilitate Up-Conversion in Red TADF Emitters That are Available for Both Vacuum- and Solution-Processes
Jia-Xiong Chen,1,2,3 Ya-Fang Xiao,2 Kai Wang,1,* Dianming Sun,1 Xiao-Chun Fan,1 Xiang Zhang,1 Ming Zhang,1 Yi-Zhong Shi,1 Jia Yu,1 Feng-Xia Geng,3 Chun-Sing Lee,2,* and Xiao-Hong Zhang1,*
1Institute of Functional Nano & Soft Materials (FUNSOM) and Jiangsu, Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, P. R. China
2Center of Super-Diamond and Advanced Films (COSDAF) and Department of Chemistry, City University of Hong Kong Hong Kong SAR, P. R. China
3College of Energy, Soochow Institute for Energy and Materials Innovations (SIEMIS), Soochow University, Suzhou 215123, P. R. China
Developing red thermally activated delayed fluorescence (TADF) emitters for high-performance OLEDs is still facing great challenge. Herein, three red TADF emitters pDBBPZ-DPXZ, pDTBPZ-DPXZ and oDTBPZ-DPXZ are designed and synthesized with same donor-acceptor (D-A) backbone with different peripheral groups attaching on the A moieties. Their lowest triplet states change from locally excited to charge transfer character leading to significantly enhance reverse intersystem crossing process. In particular, oDTBPZ-DPXZ exhibits efficient TADF feature and exciton utilization. It not only achieves an external quantum efficiency (EQE) of 20.1% in red vacuum-processed OLED, but also realize a high EQE of 18.5% in a solution-processed OLED, which is among the best results in solution-processed red TADF OLEDs. This work provides an effective strategy for designing red TADF molecules by managing energy level alignments to facilitate the up-conversion process and thus enhance exciton harvesting.