Synergistic Integration of Lithium Doping and Chloride Passivation in ZnMgO Electron Transport Layers Enables Efficient and Ultra‐Bright Blue QLEDs

ABSTRACT Quantum dot light‐emitting diodes (QLEDs) are promising for cost‐effective and color‐saturated lighting and display applications. As a key to realizing full‐color emission of the emerging technology, blue QLEDs usually exhibit inferior performance compared with their red and green counterparts, stemming from additional challenges in achieving efficient and balanced charge injection in state‐of‐the‐art devices. Herein, we develop a lithium chloride (LiCl)‐assisted approach to simultaneously modulate defect and electrical properties of commonly used magnesium‐doped zinc oxide (ZnMgO) nanocrystals, enabling blue QLEDs with obviously enhanced performance. We demonstrate that the chlorine ions of LiCl induce effective defect passivation of resultant nanocrystals, which effectively alleviates problematic interfacial exciton quenching between ZnMgO and the emissive layer. Meanwhile, the LiCl‐induced modulations on the electrical property and energy level structure of ZnMgO ensure enhanced charge‐injection balance in resultant devices. The champion QLED with emission peaking at 471 nm demonstrates a high external quantum efficiency (EQE) of 17.0% and a maximum luminance of 145,153 cd/m 2 at a low driving voltage of 6 V, representing one of the best‐performing blue QLEDs reported to date. Moreover, the device shows a measured T 95 lifetime of 12.5 h at 1,092 cd/m 2 , which is over five‐fold improvement than devices using conventional ZnMgO nanocrystals.