DFT-based investigation on novel lead-free inorganic cubic halide double perovskite Cs2LiInX6 (X = Br and I) for energy harvesting device applications

Abstract

Lead-free cubic inorganic halide double perovskites are a promising class of materials for photovoltaics and optoelectronics device applications due to their tunable band gaps and good light absorption properties. In this work, we present a theoretical analysis of the structural, electronic, elastic, and optical properties of lead-free cubic halide double perovskite Cs₂LiInX₆ (X = Br and I) using Density Functional Theory (DFT). The structural stability of the compounds is evaluated from Goldschmidt's tolerance, and the thermodynamic stability is assessed using formation, cohesive, and decomposition energies. Band gaps are found to be direct from the band structure plots using PBE-GGA, TB-mBJ, and TB-mBJ + SOC approximations with values 1.54, 2.82, and 2.72 for Cs₂LiInBr₆ and 0.42, 1.26, and 1.08 for Cs₂LiInI₆. The effective masses and DOS were also calculated, and the dynamic stability of the compounds was assessed using the phonon dispersion curve plots. The mechanical parameters are calculated as Cs₂LiInBr₆ exhibits ductility, while Cs₂LiInI₆ shows brittleness. Thermal parameters, such as the Debye and melting temperatures, are also calculated. Optical properties reveal good absorption in the visible and the UV regions in the order of 10⁵ cm⁻¹, which signifies their application as photo absorbers in tandem solar cells and as UV-related optoelectronic devices.