Lead-free perovskites InSnX₃ (X = Cl, Br, I) for solar cell applications: a DFT study on the mechanical, optoelectronic, and thermoelectric properties

This study aims to explore for the first time the mechanical, electronic, optical and thermoelectric properties of cubic lead-free perovskites InSnBr3 and InSnI3 to investigate their potential applications in solar cell devices. Additionally, the previously examined InSnCl3 perovskite is also included. The properties of the perovskites were determined using first-principles calculation based on the well-known Density Functional Theory (DFT) with the Generalized Gradient Approximation (GGA) functional implemented in the Quantum Espresso package. One of the most important findings was that the bandgaps of the compounds decrease and undergo an indirect-to-direct bandgap transition when Cl is replaced by Br and I. This indicates that InSnBr3 and InSnI3 perovskites are more suitable for solar cell applications. The bandgap energies for InSnCl3, InSnBr3, and InSnI3 perovskites are 0.59 eV (R?X), 0.44 eV (R?R), and 0.24 eV (R?R), respectively. The improved band gaps using the HSE06 functional are 2.35 eV, 2.13 eV, and 2.01 eV for the respective perovskites. The materials were found to possess chemical, mechanical, and thermodynamic stability as well as ductile behaviour. Furthermore, the materials exhibit remarkable optical properties, including high absorption coefficients and relatively small reflectivity. The calculated thermoelectric properties indicated high electrical conductivity and reasonable figure of merit values, making them promising candidates for the application in thermoelectric devices.