Discovery of new crystal structures of iodide perovskites CsPbI3 and RbPbI3 using density functional theory

Abstract

Iodine-based lead halide perovskites exhibit numerous potential phase transition structures that are challenging to identify experimentally. This study utilized density functional theory (DFT) to evaluate around 740 structural prototypes, identifying 13 possible crystal structures for CsPbI₃ and 2 for RbPbI₃, with the Cmcm structure of RbPbI₃ reported for the first time. Frozen phonon analysis reveals that CsPbI₃ does not possess any dynamically stable structures within these low-energy structures, while the Cmcm structure of RbPbI₃ exhibits adequate dynamical stability. The variation in Gibbs free energy indicates that the Pnma structure of RbPbI₃ will transform to the Cmcm structure at a temperature of 120 K. Furthermore, we calculated the band structure and optical properties. Band structure calculations indicate that CsPbI₃ possesses six direct bandgap structures, whereas RbPbI₃ displays indirect bandgap properties. The analysis of optical property analysis reveals a positive relationship between the bandgap and photon energy. While structures with larger bandgaps show superior optical qualities, those with smaller bandgaps respond optically more quickly.