Phenylene-bridged cyclic multi-resonance TADF emitters for high-efficiency and high-color-purity sky-blue OLEDs with EQE of 30%

Abstract

Although multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters exhibit near-unity photoluminescence quantum yield (PLQY) and narrow-band emission, their aggregation-caused quenching (ACQ) and random molecular orientation in organic light-emitting devices (OLEDs) restrict the maximization of their full potential. In this study, we developed a series of novel phenylene-bridged MR-TADF emitters with varying numbers of carbazole units. These emitters exhibited sky-blue emission at approximately 480 nm with a near-unity PLQY, a small full width at half maximum of 26–31 nm, and horizontal molecular orientation of θ ∼ 80%. The chemical modifications with a phenylene bridge and varied carbazole units reduced the ACQ behavior at high concentration ratios and greatly enhanced the θ values from 62% to 80%. The corresponding OLED exhibited an external quantum efficiency of approximately 30%.