Investigation on the phase transition, geometric and electronic properties of Bi-doped CsPbBr₃ perovskites

Given the ongoing debate regarding the potential impact of Bi dopant on the phase transition of CsPbBr3, our study aims to provide a comprehensive understanding of this phenomenon. Through a multifaceted examination encompassing energetic states, geometric configurations, bonding interactions, and electronic structures, we find that the inclusion of Bi dopants alone does not directly induce the orthorhombic/tetragonal phase transition in CsPbBr3. However, we observe a obvious reduction in the energetic discrepancy between these two phases, indicating an indirect stimulation of the phase transition by Bi dopants. This accelerates the stimulations originating from external environment, which may be responsible for the experimentally observed phase transition. Moreover, our investigation confirms that Bi dopants selectively weakens the bonding interaction within the Pb/Bi octahedra of the CsPbBr3 lattice in an anisotropic manner. Specifically, we identify that the weakening of the out-of-plane Bi-Br bond strength arises from the diminished bonding interaction between the p orbital of Bi and the s orbital of Br. This phenomenon results in the elongation of the metal-halide octahedra, consequently relaxing lattice distortions and twists in undoped CsPbBr3 systems, particularly pronounced in orthorhombic phases. Consequently, both orthorhombic and tetragonal CsPbBr3 lattices tend to evolve towards similar geometric configurations. Our findings reveal the significant influence of Bi dopants on the phase dynamics of CsPbBr3, a factor often overlooked in previous investigations.