Effects of Halide Composition on the Self-Recovery of Photodegraded Cesium Lead Halide Perovskite Nanocrystals: Implications for Photoluminescence Applications

Photodegraded CsPbBr3 perovskite nanocrystals (NCs) can exhibit complete self-recovery following storage in the dark. This behavior results from the readsorption of surface ligands that experienced photoinduced desorption under UV light excitation. In the present work, mixed-halide CsPb(Cl0.4Br0.6)3, CsPb(Cl0.2Br0.8)3, and CsPb(Br0.7I0.3)3 NCs were prepared via ion exchange to evaluate the influence of halide composition on the photodegradation and self-recovery of NCs. Partially substituting Cl- for Br- enhanced the photoactivation, which improved the photoluminescence properties by optimizing the adsorption state of the surface ligands during light excitation. In contrast, partially substituting I- for Br- reduced the stability of the cubic crystal structure, thus subjecting the NCs to irreversible degradation (likely including a partial phase transition) and preventing their self-recovery. Cycle tests confirmed the reversibility of the photodegradation/self-recovery of CsPbBr3 NCs; however, this behavior was disturbed by irreversible surface oxidation reactions when the sample was exposed to ambient air. Therefore, it was concluded that ambient air must be excluded to effectively take advantage of the self-recovery phenomenon for practical applications.