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 CsPbBrxCl3-x nanocrystals under the presence of an impurity metal halides, such as ZnBr2, as halide source. Our findings show that the reactions can be prolonged over 90 min at elevated temperature when ZnBr2 is added as bromine source, while addition of PbBr2 cannot work to extend the reaction. In CsPbBrxCl3-x nanocrystals synthesized under the presence of ZnBr2, it turned out that photoluminescence quantum yield gradually increases due to effective passivation of halide vacancies over reaction. In addition, air and thermal stabilities, which are strongly associated with the compositions, were significantly enhanced. Finally, we demonstrate blue-emitting light-emitting diodes based on these nanocrystals, exhibiting greatly suppressed phase segregation even under high operating voltage.