Red/Near-Infrared Thermally Activated Delayed Fluorescence OLEDs with Near 100% Internal Quantum Efficiency
Jia-Xiong Chen1,2,3, Wen-Wen Tao1, Wen-Cheng Chen2, Ya-Fang Xiao2, Kai Wang1,*, Chen Cao2, Jia Yu1, Shengliang Li2, Feng-Xia Geng3, Chihaya Adachi4, Chun-Sing Lee2,*, 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 Chemistry, Chemical Engineering and Materials Science Soochow University, Suzhou 215123 (P. R. China)
4Department of Applied Chemistry, Center for Organic Photonics and Electronics Research (OPERA), Kyushu University 744 Motooka, Nishi, Fukuoka 819-0395 (Japan)
Developing red thermally activated delayed fluorescence (TADF) emitters, attainable for both high-efficient red organic light-emitting diodes (OLEDs) and non-doped deep red/near-infrared (NIR) OLEDs, is challenging. Now, two red emitters, BPPZ-PXZ and mDPBPZ-PXZ, with twisted donor–acceptor structures were designed and synthesized to study molecular design strategies of high-efficiency red TADF emitters. BPPZ-PXZ employs the strictest molecular restrictions to suppress energy loss and realizes red emission with a photoluminescence quantum yield (FPL) of 100 ± 0.8% and external quantum efficiency (EQE) of 25.2% in a doped OLED. Its non-doped OLED has an EQE of 2.5% owing to unavoidable intermolecular π–πinteractions. mDPBPZ-PXZ releases two pyridine substituents from its fused acceptor moiety. Although mDPBPZ-PXZ realizes a lower EQE of 21.7% in the doped OLED, its non-doped device shows a superior EQE of 5.2% with a deep red/NIR emission at peak of 680 nm.