Flexible all fluorescence white organic light emitting device with over 22% EQE by stepped reverse intersystem crossing channels based on ternary exciplex

摘要

Improvement of the utilization of triplet excitons for thermally activated delayed fluorescence (TADF) emitter-based white organic light emitting devices (WOLEDs) is a key scientific challenge. In this study, a new strategy with stepped reverse intersystem crossing (RISC) channels induced by new ternary exciplex was proposed to enhance up-conversion of non-radiative triplet excitons. A flexible TADF WOLED with external quantum efficiency (EQE) of 22.7% and a power efficiency of 62.5 lmW~(-1) was demonstrated. At 1000 cdm~(-2), the EQE still remained at 21.4%, showing low efficiency roll-off of 5.7%. It is attributed to the reduced non-radiative triplet excitons stack, which suppressed the triplet-triplet quenching. Moreover, the new ternary exciplex-based WOLED system mCP: DMAC-DPS:PO-T2T:4CZPNPh exhibited rate constant of RISC process of 2.5 × 10~6 s~(-1), and about 2 times photoluminescence quantum yield over binary exciplex. The high efficiency effectively demonstrated that the proposed multiple triplet excitons capture process is an effective strategy to improve the utilization of triplet excitons. Moreover, the novel strategy can be a promising approach for the further development of WOLED.