Thermoelectric and optoelectronic properties of novel lead-free halide perovskites CsRbTiX6 (X= I, Br and Cl) for photovoltaic applications

Abstract

Motivated by the physical properties of halide perovskites. The density functional theory was used to investigate the structural stability, elastic, electronic, optical and thermoelectric properties of new perovskites CsRbTiX6 (X = I, Br and Cl). The obtained results from the ground state show that the calculated lattice parameter a0 and Ti-X bond length decrease progressively when X goes from I to Cl. The elastic constants and their derived parameters like Young's modulus, shear modulus, Poisson's ratio and the anisotropic factor show high mechanical stability, brittle behavior and elastic anisotropy nature. The electronic profile shows a semiconducting nature with an indirect band gap and the values of the band gap decrease when X goes from Cl to Br and then to I. Thermoelectric properties are reported and found to increase with temperature, which also demonstrates the semiconducting nature with electrons as the majority carriers. The optical parameters reveal high light absorption and low reflectivity, particularly in the visible light range. The mechanical stability, strong absorption and low reflectivity in the visible and ultra-violet regions make these materials more suitable for optoelectronic applications.