Optimizing Charge Transfer and Out‐Coupling of A Quasi‐Planar Deep‐Red TADF Emitter: towards Rec.2020 Gamut and External Quantum Efficiency beyond 30 %

Abstract Herein, we report a deep‐red TADF emitter p CNQ–TPA , composed of quinoxaline‐5,8‐dicarbonitrile ( p CNQ) 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.