Influence of different rotations of organic formamidinium molecule on electronic and optical properties of FAPbBr₃ perovskite

Hybrid organic–inorganic halide perovskites (HOIPs) have recently represented a material breakthrough for optoelectronic applications. Obviously, studying the interactions between the central organic cation and the Pb-X inorganic octahedral could provide a better understanding of HOIPs. In this work, we used a first-principles theoretical study to investigate the effect of different orientations of central formamidinium cation (FA⁺) on the electronic and optical properties of FAPbBr₃ hybrid perovskite. In order to do this, the band structure (with and without spin– orbit coupling (SOC)), density of states (DOS), partial density of states (PDOS), electron density, distortion index, bond angle variance, dielectric function, and absorption spectra were computed. The findings revealed that a change in the orientation of FA⁺ caused some disorders in the distribution of interactions, resulting in the formation of some specific energy levels in the structure. The interactions between the inorganic and organic parts in different directions create a distortion index in the bonds of the inorganic octahedral, thus leading to a change in the volume of PbBr₆. This is the main reason for the variations observed in the electronic and optical properties of FAPbBr₃. The obtained results can be helpful in solar-cell applications.