High-performance non-doped deep-blue/white OLEDs via HLCT-type oxazole emitter with negligible efficiency roll-off

Stable deep-blue emitters with high-efficiency and low-efficiency roll-off are crucial for the commercialization of deep-blue organic light-emitting diodes (OLEDs). Hybridized local and charge-transfer (HLCT) emitters can achieve high external quantum efficiency (EQE) and extremely low efficiency roll-off through efficient high-lying reverse intersystem crossing. In this work, we developed a simple, efficient deep-blue HLCT emitter, PBOAn2N, which exhibited an emission peak at 446 nm with CIE coordinates of (0.131, 0.086). The related OLED device achieved the maximum EQE of 9.7%, demonstrating an exceptionally low efficiency roll-off of merely 1.0% at 1000 cd m−2. Furthermore, when employed as a host material for an orange phosphorescent emitter, PBOAn2N demonstrated exceptional performance with a maximum EQE of 25.7% and an ultralow efficiency roll-off of merely 0.4% at 1000 cd m−2. By integrating a PBOAn2N-based blue-emitting layer into the orange phosphorescent system, we fabricated a two-color hybrid WOLED with minimal roll-off (2.3% at 1000 cd m−2), achieving near-ideal CIE coordinates approaching (0.333, 0.333). Notably, the optimized device attained a record-high color rendering index of 68.4, representing one of the best performances reported for two-color hybrid WOLEDs, thereby showcasing the significant potential of PBOAn2N-based systems for high-quality white light emission applications.