Spin‐Flip‐Restricted Multiple‐Resonance Emitters for Extended Device Lifetime in Indolocarbazole‐Based Blue Organic Light‐Emitting Diodes

Abstract In this study, a multiple‐resonance (MR) core structure is developed with a spin‐flip‐restricted emission mechanism based on a fused indolo[3,2,1‐ jk ]carbazole (ICz) framework as emitters to improve the lifetime of blue organic light‐emitting diodes. The molecular skeleton modulation approach applied to the conjugated π ‐system effectively stabilizes the triplet energy of the fused ICz emitters and narrows the full‐width‐at‐half maximum (<20 nm). In addition, the emitters exhibit higher exciton stability than conventional boron‐based MR emitters. The fused ICz‐based blue fluorescent device exhibits a high external quantum efficiency of 7.2%, a blue index of 68.6 cd A −1 at a Commission internationale de l'éclairage y coordinate (CIE y ) of 0.075, and a device lifetime 1.8 times longer than that of a boron‐based emitter. In addition, a phosphor‐sensitized fluorescent device based on the ICz emitter exhibited an improved external quantum efficiency of 20.6% with a CIE y coordinate of 0.076.