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

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 (EQEmax ) 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 EQEmax 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.