Quenching‐Resistant Multiresonance TADF Emitter Realizes 40% External Quantum Efficiency in Narrowband Electroluminescence at High Doping Level

Abstract

Abstract Multiresonance thermally activated delayed fluorescence (MR‐TADF) emitters manifest great potential for organic light‐emitting diodes (OLEDs) due to their high exciton‐utilization efficiency and narrowband emission. Nonetheless, their tendency toward self‐quenching caused by strong interchromophore interactions would induce doping sensitivity and deteriorate the device performances, and effective strategy to construct quenching‐resistant emitters without sacrifycing color purity is still to be developed. By segregating the planar MR‐TADF skeleton using two bulky carbazolyl units, herein a highly emissive molecule with enhanced quenching resistance is reported. The steric effect largely removes the formation of detrimental excimers/aggregates, and boosts the performance of the corresponding devices with a maximum external quantum efficiency (EQE max ) up to 40.0% and full width at half maximum (FWHM) of 25 nm, representative of the only example of single OLED that can concurrently achieve narrow bandwidth and high EL efficiency surpassing 40% to date. Even at doping ratio of 30 wt%, the EQE max is retained to be 33.3% with nearly unchanged emission spectrum. This work provides a viable approach to realize doping‐insensitive MR‐TADF devices with extreme EL efficiency and color purity for high‐end OLED displays.