Helical Multi‐Resonance Thermally Activated Delayed Fluorescence Emitters for High‐Performance Anti‐Quenching Narrowband Blue OLEDs

ABSTRACT Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) has established a new approach for narrowband blue organic light emitting diodes (OLEDs), yet effectively suppressing intermolecular interactions especially at high doping concentrations while preserving the intrinsic narrowband emission remains a formidable challenge. Herein, a novel designing paradigm is proposed for achieving anti‐quenching narrowband emission in MR‐TADF molecules by embedding the indeno[2,1‐b]carbazole unit into the polycyclic aromatic hydrocarbon skeleton. The proof‐of‐concept emitter DT‐BON1 reveals a favorable twist angle of 31.8°, manifesting formation of helical architecture within MR core. As a result, the emission peaks and full width at half maximum show virtually no variation with changing doping concentration from 1 wt% to 20 wt%. Moreover, the photoluminance quantum yields exceed 90% even at 20 wt% doping concentration endowed by the outstanding anti‐quenching characteristics. The DT‐BON1 based OLEDs can achieve maximum external quantum efficiency (EQE max ) of exceeding 30%. Especially, the alleviated exciton quenching effects can be firmly demonstrated by marginally decreased EQE max values, attaining 29.2% in 10 wt%‐based OLEDs and 27.3% even in heavily doped devices (20 wt%), which is at a record high for MR‐TADF with blue emission at such high doping concentration.