Metastable γ-CsPbI3 Perovskite Nanocrystals Created Using Aged Orthorhombic CsPbBr3

Research on anion exchange reactions (AERs) indicated that the reaction rate has a significant influence on the photoluminescence properties and crystal structures of the resulting CsPb(Br/I)3 nanocrystals (NCs). Controllable AERs were achieved by controlling the reaction rate. Using controllable AERs, metastable γ-CsPbI3 NCs were directly obtained from the aged orthorhombic CsPbBr3 NCs. Rietveld refinement indicated that the crystal structure of parent CsPbBr3 was maintained without any phase transition or degradation. The prepared γ-CsPbI3 NCs exhibited good stability at room temperature. X-ray photoelectron spectroscopy analysis demonstrated the presence of Br and the high binding energy of Pb–Br bonding. Pb–Br bonds maintained the parent orthorhombic CsPbBr3 structure and increased the stability of γ-CsPbI3 NCs. Controllable AERs provide versatile methods to maintain the parent perovskite structure and synthesize CsPbI3 NCs with a more rigid crystal structure. They pave the way for the preparation of NCs, which are difficult to synthesize directly.