Blue‐hazard‐free single‐emissive‐layer white organic LEDs based on an anti‐quenching narrowband blue emitter

Abstract Blue photons below 450 nm pose risks to visual health, while conventional lighting devices unavoidably emit in this region. Existing solutions often involve intricate emissive‐layer designs or suffer from low efficiency. Here, we present blue‐hazard‐free single‐emissive‐layer white organic light‐emitting diodes (WOLEDs) employing a newly developed multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) emitter, BNCT, as an anti‐quenching blue emitter and efficient energy donor. BNCT integrates a sky‐blue MR‐TADF core with a sterically hindered, electron‐rich arylamine donor, effectively suppressing π–π stacking and aggregation‐induced quenching while maintaining narrowband emission (486 nm, bandwidth = 26 nm) entirely above 450 nm. The finely tuned donor–acceptor interaction enables controlled charge‐transfer characteristics and accelerates reverse intersystem crossing, ensuring efficient exciton utilization. When co‐doped with yellow and red phosphorescent dopants in a single emissive layer, the resulting devices deliver balanced warm‐white emission with CIE coordinates of (0.31, 0.44)–(0.40, 0.43), correlated color temperatures of 6013–4734 K, and negligible blue‐hazard photon ratios (<0.2%). Remarkably, the devices achieve high efficiencies up to 27.8% external quantum efficiency. This work establishes a robust molecular design paradigm for anti‐quenching MR‐TADF emitters and advances the development of high‐efficiency, eye‐safe WOLEDs for next‐generation healthy lighting and display technologies.