Density Functional Theory Assessment of the Structural, Electronic and Optical Properties of Lead-Free KSnI₃ Perovskite

Abstract

Lead-free halide perovskites are of interest for optoelectronic applications, but the electronic and optical properties of potassium tin iodide (KSnI₃) require further assessment. Here, we performed density functional theory calculations using Quantum ESPRESSO 7.2 to examine its structural, electronic, and optical properties. The optimised structure yielded a characteristic lattice parameter of approximately 6.30 Å. The calculated band gap was approximately 0.75 eV, indicating semiconducting behaviour; this GGA-PBE result is method-dependent, and spin–orbit coupling was not included. The density of states indicates that iodine 5p states dominate the valence-band region, with tin 5s hybridisation, while tin 5p states contribute strongly to the conduction band. Optical calculations show a weak response below approximately 2.52 eV, followed by increased absorption and stronger dielectric and related optical features at higher photon energies. These results provide a theoretical description of KSnI₃ and motivate further study. The optimised structure and bulk DFT results alone do not establish thermodynamic stability or photovoltaic device performance; phase competition, lattice dynamics, spin-orbit effects, and experimental or device-level validation remain important avenues for future work.