Customizing the optical, electronic and transport attributes of lead-free hybrid FASnBr perovskites triggered by spin-orbit coupling and strains.

Organic-inorganic hybrid halide perovskites are emerging as promising materials for solar energy due to their unique structures and electronic properties. However, the commonly studied MAPbI and FAPbI are toxic and less stable, prompting the necessity for safer replacements. Using the density functional theory (DFT), this study explored the effects of strains and spin-orbit coupling (SOC) on Sn-based FASnBr perovskites and the accuracy and validity of the obtained results were confirmed with the existing experimental results. The FASnBr perovskites paraded direct bandgaps of 1.20 eV without SOC and 0.89 eV with SOC. The tensile strains upsurged the bandgaps, while compressive strains reduced them. The SOC significantly diminished the bandgaps and effective carrier mass, and 8 % of compressive strains with SOC showed unique bandgap behaviour. For unstrained FASnBr perovskites, the real dielectric constant was 4.4 at zero photon energy, with a peak of 6.5 in the visible range. The maximum loss occurred at a photon energy of 21.88 eV. It was also observed that the tensile strain increases the loss to 1.46 at 20.20 eV. The tensile strains also increased absorption, while compressive strains caused a redshift in the dielectric function, loss spectrum, and absorption peaks. Due to their excellent optical and electronic properties, FASnBr perovskites are considered highly promising for lead-free optoelectronic applications like LEDs, solar panels, lasers, and optical detectors.