Pressure dependence of the structural and optoelectronic properties of Pb-free perovskites LiSnX3 (X = Br and Cl): A DFT approach

In this study, the structural, electronic and optical properties of cubic lead-free halide perovskites LiSnX₃ (X = Br and Cl) under hydrostatic pressure are investigated. The first-principle approach based on density functional theory (DFT) is employed. The exchange-correlation functional is treated using the generalized gradient approximation (GGA), specifically a variant of the Perdew-Burke-Ernzerhof (PBE) method. The aim of the study is to understand the effect of pressure on the properties of LiSnX₃ (X = Br and Cl), with a maximum pressure limit of 6 GPa. The results show a decreasing tendency in the energy band gap as pressure increases. In addition, a prominent reduction in the energy band gap is observed when the halogen atom is changed from Cl to Br under constant pressure. The calculations also investigate the density of states (DOS), showing variations in energy levels near the Fermi level under different pressures. For optical properties, density functional perturbation theory (DFPT) is used in conjunction with the Kramers-Kronig relation. Optical parameters such as the real and imaginary parts of the dielectric constant, refractive index, absorption coefficient, and wavelength are computed under different pressures to understand the optical response of the perovskites to the electromagnetic spectrum. The insights from this study highlight the fundamental properties of LiSnX₃ (X = Br and Cl) under different pressures, which could influence advancements in optoelectronic devices, photonic applications, and solar cell technologies. Moreover, this research contributes to the growing body of knowledge on lead-free halide perovskites, encouraging further developments in the field.