Halide vacancy passivation in cesium lead halide perovskite nanocrystals with mixed halide compositions: the impact of prolonged reaction time

Abstract

Perovskite nanocrystals offer a significant advantage in covering the entire visible spectrum with outstanding color purity by simply tuning their halide compositions, making them highly desirable for light-emitting diode applications with excellent color reproducibility. However, mixed halide perovskite nanocrystals often suffer from instability issues, such as halide segregation under various stimuli. In this study, we present a straightforward synthetic approach to produce stable blue-emitting perovskite nanocrystals with mixed halide compositions. Specifically, we synthesized blue-emitting CsPbBr_xCl_3−x nanocrystals in the presence of impurity metal halides, such as ZnBr₂, as halide sources. Our findings show that the reaction can be prolonged for over 90 min at elevated temperature when ZnBr₂ is added as a bromine source, while the addition of PbBr₂ fails to extend the reaction. In CsPbBr_xCl_3−x nanocrystals synthesized in the presence of ZnBr₂, it turned out that the photoluminescence quantum yield gradually increases due to effective passivation of halide vacancies over time during the reaction. In addition, air and thermal stabilities, which are strongly associated with the compositions, were significantly enhanced. Finally, we demonstrate blue light-emitting diodes based on these nanocrystals, exhibiting greatly suppressed phase segregation even under high operating voltage.