Rigid Oxygen‐Bridged Boron‐Based Blue Thermally Activated Delayed Fluorescence Emitter for Organic Light‐Emitting Diode: Approach towards Satisfying High Efficiency and Long Lifetime Together

Thermally activated delayed fluorescence (TADF) materials have emerged as an efficient emitter for achieving high efficiency of blue organic light emitting diodes (OLEDs). However, it is challenging to satisfy both high device efficiency and long operational lifetime together. Here, highly efficient and electrochemically stable blue TADF emitter, 5‐(5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)‐10,15‐diphenyl‐10,15‐dihydro‐5H‐diindolo[3,2‐a:3′,2′‐c]carbazole (DBA‐DI) is designed and synthesized for high efficiency and long lifetime OLED. This emitter exhibits high photoluminescence quantum yield of 95.3%, small single‐triplet energy gap of 0.03 eV, short delayed exciton lifetime of 1.25 µs, and high bond dissociation energy (BDE). Also, phosphine oxide free high triplet energy host systems (single and mixed) and exciton blocking layer materials are analyzed using molecular and optical simulations to find an efficient host system with high BDE and suitable emission zone for high efficiency and stable OLEDs. The fabricated OLED with DBA‐DI and high triplet host exhibited a maximum external quantum efficiency (EQE) of 28.1% with blue CIE color coordinates of (0.16, 0.39) and long operational lifetime (LT50) of 329 h at the initial luminance of 1000 cd m−2. Furthermore, the mixed host‐based TADF device showed a slightly lower EQE of 26.4% and almost two times longer lifetime (LT50: 540 h) than the single host device. This work reports a highly efficient and stable thermally activated delayed fluorescence (TADF) emitter for blue organic light‐emitting diode (OLED). The fabricated TADF‐OLED exhibited both high external quantum efficiency (26.4%) and long device lifetime (540 h at the initial brightness of 1000 cd m−2) together due to the short‐delayed lifetime, small ΔEST, high bond dissociation energy of emitter, and well‐controlled emission zone.