High-Performance Solution-Processed Red Thermally Activated Delayed Fluorescence OLEDs Employing Aggregation-Induced Emission-Active Triazatruxene-Based Emitters
Yang Liu, Yonghong Chen, Hua Li, Shuai Wang, Xiaofu Wu, Hui Tong, Lixiang Wang
Abstract
Two novel red thermally activated delayed fluorescence (TADF) emitters [triazatruxene (TAT)–dibenzo[a,c]phenazine (DBPZ) and TAT–fluorine-substituted dibenzo[a,c]phenazine (FDBPZ)] were developed by incorporating TAT as the electron donor (D) and DBPZ or FDBPZ as the electron acceptor (A). Both compounds showed aggregation-induced emission behaviors and bright red emission in neat films. Benefited from the rigid and large planar conjugated structure of TAT and DBPZ, TAT–DBPZ and TAT–FDBPZ realized high photoluminescence quantum yields in solid states. Meanwhile, the large steric hindrance between TAT and DBPZ segments produced small singlet–triplet energy splitting (ΔEST), leading to short delayed fluorescence lifetimes and high reverse intersystem crossing (RISC) rate (>106 s–1) for both compounds. The solution-processable doped organic light-emitting diodes (OLEDs) based on TAT–DBPZ achieved a high external quantum efficiency (EQE) of 15.4% with a red emission peak at 604 nm, which was one of the highly efficient solution-processable red TADF OLEDs. TAT–FDBPZ-based doped devices also showed a red emission peak at 611 nm with a maximum EQE of 9.2% and low-efficiency roll-off ratios of 1.0% at 100 cd m–2 and 19% at 1000 cd m–2. Furthermore, their solution-processable nondoped devices displayed EQEs of 5.6 and 2.9% with the red-shifted emission peaks at 626 and 641 nm, respectively. These results indicate the huge potential of utilization of TAT as the donor unit to achieve highly efficient and low-efficiency roll-off solution-processable red TADF OLEDs.