Novel Multiple Resonance Type TADF Emitter as Blue Component for Highly Efficient Blue‐Hazard‐Free White Organic Light‐Emitting Diodes

Abstract Realizing blue‐hazard‐free emission is an important goal for white organic light‐emitting diodes (OLEDs) toward healthy lighting applications. However, conventional blue organic emitters with broad emission spectra would generally cover the high‐energy emission region and thus cannot meet the demand. Here a blue multiple resonance type thermally activated delayed fluorescence (TADF) emitter DPMX‐CzDABNA is newly designed. The DPMX‐CzDABNA‐based OLEDs can realize blue narrowband emission peaked at 484 nm with a full width at half maximum of 29 nm, and external quantum efficiencies (EQEs) around 26%, which allows DPMX‐CzDABNA to precisely avoid the high‐energy photon contribution and thus be a promising blue component to construct high‐performance white OLEDs with human‐eye‐friendly emission spectra. Using DPMX‐CzDABNA and a reported TADF emitter BPPZ‐DPXZ, respectively, as blue and orange components in white OLEDs, the single‐emitting‐layer devices approach white emission with outstanding EQE up to 35.8%; the double‐emitting‐layer OLEDs achieve blue‐hazard‐free white emissions with a maximum EQE of 26.5% and very stable Commission Internationale de l'Eclairage coordinates of ≈(0.38,0.43) over a wide luminance range from 100 to 10 000 cd m −2 . It is expected that this strategy can pave a new way for developing highly efficient all‐TADF white OLEDs without blue‐hazard emission.