Novel Strategy to Develop Exciplex Emitters for High-Performance OLEDs by Employing Thermally Activated Delayed Fluorescence Materials

To develop high-performance thermally activated delayed fluorescence (TADF) exciplex emitters, a novel strategy of introducing a single-molecule TADF emitter as one of the constituting materials has been presented. Such a new type of exciplex TADF emitter will have two reverse intersystem crossing (RISC) routes on both the pristine TADF molecules and the exciplex emitters, benefiting the utilization of triplet excitons. Based on a newly designed and synthesized single-molecule TADF emitter MAC, a highly efficient exciplex emitter MAC:PO-T2T has been obtained. The device based on MAC:PO-T2T with a weight ratio of 7:3 exhibits a low turn-on voltage of 2.4 V, high maximum efficiency of 52.1 cd A⁻¹ (current efficiency), 45.5 lm W⁻¹ (power efficiency), and 17.8% (external quantum efficiency, EQE), as well as a high EQE of 12.3% at a luminance of 1000 cd m⁻². The device shows the best performance among reported organic light-emitting devices based on exciplex emitters. Such high-efficiency and low-efficiency roll-off should be ascribed to the additional reverse intersystem crossing process on the MAC molecules, showing the advantages of the strategy described in this study.