Composition related structural transition between mechanosynthesized CsPbBr3 and CsPb2Br5 perovskites and their optical properties

A facile solvent-free mechanochemical synthesis mechanism of perovskites of Cs–Pb–Br system has been demonstrated in the present study. Inherent structural and microstructural characteristics of CsPbBr3 and CsPb2Br5 perovskites are investigated by analyzing powder XRD patterns using Rietveld refinement analysis and formation of these perovskites has been ascertained. The compositional phase transition between orthorhombic CsPbBr3 and tetragonal CsPb2Br5 perovskites has been explained from the structural point of view. The optically active orthorhombic CsPbBr3 perovskite transforms to optically inactive tetragonal CsPb2Br5 perovskite under flowing water vapour within a short duration and the reverse transformation is noticed when the tetragonal perovskite is heat-treated at elevated temperature. Optical properties of these perovskites corroborate well with structural phase transitions of these compounds. This new approach of structural conversion not only provides a controlled synthesis of the ternary Cs–Pb–Br system but also demonstrates a clear underlying mechanism for the structural instability and associated optical properties.