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A deep-red TADF emitter p CNQ–TPA for UHD display was demonstrated, which realized the desired chromaticity matching rec.2020 standard and the record external quantum efficiency beyond 30 %. It is showed that its quasi-planar structure not only improves horizontal ratio of emitting dipole orientation for out-coupling enhancement, but also balances the intra- and inter-molecular charge transfer for radiation facilitation and quenching suppression.

Abstract

Herein, we report a deep-red TADF emitter p CNQ–TPA, composed of quinoxaline-5,8-dicarbonitrile (pCNQ) acceptor and triphenylamine (TPA) donor. p CNQ–TPA supported its OLED with desired CIE coordinates of (0.69, 0.31) and the record maximum external quantum efficiency of 30.3 %, which is the best red TADF diode with Rec.2020 gamut for UHDTV. It is showed that through tuning p CNQ–TPA doping concentration, intra- and inter-molecular charge transfer are balanced to synchronously improve emission color saturation and TADF radiation, and remedy aggregation-induced quenching, rendering photoluminescence quantum yield (PLQY) reaching 90 % for deep-red emission peaked at ≈690 nm. Quasi-planar structure further endows p CNQ–TPA with an improved horizontal ratio of emitting dipole orientation, which increases light out-coupling ratio to 0.34 for achieving the state-of-the-art device efficiencies.