Asymmetric Structural Engineering of Hot‐Exciton Emitters Achieving a Breakthrough in Non‐Doped BT.2020 Blue OLEDs with a Record 9.5% External Quantum Efficiency

Abstract High‐efficiency non‐doped deep‐blue organic light‐emitting diodes (OLEDs) meeting the standard of BT.2020 color gamut is desired but rarely reported. Herein, an asymmetric structural engineering based on crossed long‐short axis (CLSA) strategy is developed to obtain three new deep‐blue emitters (BICZ, PHDPYCZ, and PHPYCZ) with a hot‐exciton characteristic. Compared to 2BuCz‐CNCz featuring a symmetric single hole‐transport framework, these asymmetric emitters with the introduction of different electron‐transport units show the enhancement of photoluminescence efficiency and improvement of bipolar charge transport capacity. Further combined with high radiative exciton utilization efficiency and light outcoupling efficiency, the non‐doped OLED based on PHPYCZ exhibits the best performance with an excellent current efficiency of 3.49%, a record‐high maximum external quantum efficiency of 9.5%, and a CIE y coordinate of 0.049 approaching the BT.2020 blue point. The breakthrough obtained in this work can inspire the molecular design of deep‐blue emitters for high‐performance non‐doped BT.2020 blue OLEDs.