Nondoped Red Fluorophores with Hybridized Local and Charge-Transfer State for High-Performance Fluorescent White Organic Light-Emitting Diodes

Two red fluorophores (TPABTPA and TPABCHO) with hybridized local and charge-transfer properties were systematically studied. TPABTPA and TPABCHO enabled nondoped organic light-emitting diodes (OLEDs) with excellent external quantum efficiency (EQE) of 11.1% and 5.0%, respectively, attributed to high exciton utilization efficiency of 82% and 46%, respectively. Furthermore, TPABTPA and TPABCHO were utilized as complementary emitters for a sky-blue thermally activated delayed fluorescence material to fabricate two-color fluorescent white OLEDs (WOLEDs) in a fully nondoped emissive-layer configuration. Furthermore, device performance was optimized through a simple device engineering strategy by sandwiching a suitable interlayer between the emitting layers. As a result, the optimized TPABTPA- and TPABCHO-based WOLEDs successfully achieved high EQEs of 23.0% and 8.6%, respectively, along with a low efficiency roll-off and good spectral stability, due to high exciton utilization efficiency of the emitters and importantly efficient suppression of a nonradiative energy-transfer process.