High-efficiency and stable short-delayed fluorescence emitters with hybrid long- and short-range charge-transfer excitations
Guoyun Meng, Hengyi Dai, Qi Wang, Jianping Zhou, Tianjiao Fan, Xuan Zeng, Xiang Wang, Yuewei Zhang, Dezhi Yang, Dongge Ma, Dongdong Zhang, Lian Duan
Abstract
Abstract The pursuit of ideal short-delayed thermally activated delayed fluorescence (TADF) emitters is hampered by the mutual exclusion of a small singlet-triplet energy gap (Δ E ST ) and a large oscillator strength ( f ). Here, by attaching an multiresonance-acceptor onto a sterically-uncrowded donor, we report TADF emitters bearing hybrid electronic excitations with a main donor-to-acceptor long-range (LR) and an auxiliary bridge-phenyl short-range (SR) charge-transfer characters, balancing a small Δ E ST and a large f . Moreover, the incorporation of dual equivalent multiresonance-acceptors is found to double the f value without affecting the Δ E ST . A large radiative decay rate over an order of magnitude higher than the intersystem crossing (ISC) rate, and a decent reverse ISC rate of >10 6 s −1 are simultaneously obtained in one emitter, leading to a short delayed-lifetime of ~0.88 μs. The corresponding organic light-emitting diode exhibits a record-high maximum external quantum efficiency of 40.4% with alleviated efficiency roll-off and extended lifetime.