Two-Channel Space Charge Transfer-Induced Thermally Activated Delayed Fluorescent Materials for Efficient OLEDs with Low Efficiency Roll-Off
Ruifang Wang, Zhiyi Li, Taiping Hu, Lei Tian, Xiaoxiao Hu, Shihao Liu, Chen Cao, Ze‐Lin Zhu, Jihua Tan, Yuanping Yi, Pengfei Wang, Chun‐Sing Lee, Ying Wang
Abstract
Enhancing the reverse intersystem crossing (RISC) process of thermally activated delayed fluorescent (TADF) emitters is an effective approach to realize efficient organic light-emitting diodes (OLEDs) with low efficiency roll-off. In this work, we designed two novel TADF emitters, SAT-DAC and SATX-DAC, via a spiro architecture. Efficient maximum external quantum efficiencies (EQEs) of 22.6 and 20.9% with reduced efficiency roll-off (EQEs of 17.9 and 17.0% at 1000 cd m–2) were achieved via a “two-RISC-channel” strategy. X-ray diffraction shows close donor (D)/acceptor (A) spacing and suitable D/A orientation in crystals of the two emitters favoring both intra- and intermolecular through-space charge transfer (TSCT) processes. Transient photoluminescence decay measurements show that both emitters have two RISC channels leading to kISCT exceeding 106 s–1. These results suggest that the “two-RISC-channel” design can be a novel approach for enhancing performance of TADF emitters, in particular at high excitation densities.