Boosting the Performance of Blue Cu–Ga–Zn–S-Based Quantum-Dot Light-Emitting Diodes through Interfacial Passivation by ZnI2

The advancement of environmentally benign I–III–VI colloidal quantum dots (QDs) has established a promising materials platform to replace cadmium-based counterparts. However, in practical device architectures, especially blue-emitting devices, abundant surface nonradiative recombination centers and imbalanced carrier injection often lead to suboptimal device performance, thereby hindering their deployment in display technologies. Herein, we employ a zinc iodide (ZnI2) post-treatment for the Cu–Ga–Zn–S (CGZS) QDs film strategy, effectively passivating surface defects and nonradiative sites, thereby enhancing device performance. The treated QDs facilitate the formation of an interface dipole, which effectively elevates the overall energy levels of the QDs while simultaneously reducing the hole injection barrier, leading to an enhanced hole injection efficiency. Working in concert, these effects facilitate balanced carrier injection and optimize exciton recombination, thereby boosting the device efficiency and operational stability. Consequently, the peak external quantum efficiency (EQE) exhibits a favorable improvement, increasing from 1.01% in the pristine device to 1.90% after treatment. This work offers an effective approach to achieving balanced carrier injection in quantum-dot light-emitting diodes (QLEDs) and establishes a solid foundation for the development of high-performance, cadmium-free, blue-emitting QLEDs.