Optimizing the horizontal dipole orientation and dipole–dipole interaction of thermally activated delayed fluorescence emitters for high efficiency and low roll-off red OLEDs

Abstract

The development of thermally activated delayed fluorescence (TADF) emitters for high efficiency and low roll-off red organic light-emitting diodes (OLEDs) is challenging. In this paper, three red TADF molecules are developed by adopting a donor–acceptor molecular architecture. It can be seen that the delayed fluorescence lifetime is dependent on the intensity and quantity of donors. Furthermore, by changing the dipole moment and regulating the intensity of charge transfer between the host and emitter, high efficiency red OLEDs with the maximum EQE of 21.1% are achieved due to the improvement of horizontal dipole orientations and charge transport balance. Through the analysis of the exciton dynamics model, the polaron–exciton annihilation is suppressed with a faster reverse intersystem crossing (RISC) process, which is highly beneficial to the improvement of efficiency roll-off at high luminance. Our results demonstrate that the selection of highly efficient TADF emitters and matched hosts is crucial for realizing high performance red TADF-based OLEDs.