Studies on the Light-Induced Phase Transition of CsPbBr₃ Metal Halide Perovskite Materials

We investigate the internal mechanism of the light-inducedphasetransition of CsPbBr3 perovskite materials via densityfunctional theory simulations. Although CsPbBr3 tends toappear in the orthorhombic structure, it can be changed easily byexternal stimulus. We find that the transition of photogenerated carriersplays the decisive role in this process. When the photogenerated carrierstransit from the valence band maximum to conduction band minimum inthe reciprocal space, they actually transit from Br ions to Pb ionsin the real space, which are taken away by the Br atoms with higherelectronegativity from Pb atoms during the initial formation of theCsPbBr(3) lattice. The reverse transition of valence electronsleads to the weakening of bond strength, which is proved by our calculatedBader charge, electron localization function, and integral value ofCOHP results. This charge transition releases the distortion of thePb-Br octahedral framework and expands the CsPbBr3 lattice, providing possibilities to the phase transition from theorthorhombic structure to tetragonal structure. This phase transitionis a self-accelerating positive feedback process, increasing the lightabsorption efficiency of the CsPbBr3 material, which isof great significance for the widespread promotion and applicationof the photostriction effect. Our results are helpful to understandthe performance of CsPbBr3 perovskite under a light irradiationenvironment.