Mutual effect of strains and spin-orbit coupling on structural, electronic, transport and optical characteristics of FASnI2Br perovskites

Energy shortages have become a global issue in the twenty-first century, as energy consumption continues to rise at an alarming rate and the fossil fuel supply is depleted. Thus, producing sustainable renewable energy to replace fossil fuels is essential to resolve energy shortages. Solar energy is the most promising, easily accessible, reusable, fresh and sustainable alternative to fossil fuels. Organic-inorganic halide perovskite solar cells (PSCs) are a rising star in third-generation photovoltaic technology, with excellent power conversion efficiencies (PCEs). However, the most extensively researched perovskites contain poisonous lead, a cumulative toxicant to human bodies that may limit their broad use. Despite multiple alternative metal ions to replace Pb, tin is used with an efficiency of over 30 %. This study uses density functional theory (DFT) to examine the strain's effect and spin-orbit coupling (SOC) on structures and properties of FASnI 2 Br perovskites. FASnI 2 Br perovskites show semiconducting behavior having a direct bandgap of 1.11 eV and 0.75 eV, excluding and including SOC, respectively. According to electronic studies, the B-site p-orbital influences the CBB (conduction band bottom), whereas the X-site p-orbitals impact the VBT (valence band top). Generally, tensile strains increase bandgaps, whereas compressive strains reduce them. The SOC reduces the bandgap and effective mass of the charge carrier. At zero frequency, the real dielectric constant value is 4.62, and the highest value is 7.19 under strain-free conditions. The highest loss values also vary depending on the strain. The maximum loss value for unstrained cubic FASnI 2 Br structure is 1.36 at a photon energy of 16.87 eV. For the no-strained structures, the absorption coefficient is 0.055 × 10 4 , which also increased with bandgap, i,e., with increasing strains. The FASnI 2 Br perovskites, with their remarkable optical and electronic properties, hold good promise for lead-free optoelectronic uses, including light-emitting diodes, solar power plants, laser beams, and optical sensors.