Lead-free halide double perovskites Rb2InSbX6 (X = F, Cl, Br, I): A first-principles study of structural and optoelectrical properties

First-principles calculation employing PBE and HSE06 hybrid functionals have been used to investigated the structural optoelectrical properties of lead-free halide double perovskite Rb2InSbX6 (X = F, Cl, Br, and I). The optical bandgaps are 2.48 eV for Rb2InSbF6, 1.18 eV for Rb2InSbCl6, 0.60 eV for Rb2InSbBr6, and 0.23 eV for Rb2InSbI6, which are all direct bandgap semiconductors. Electronic structure calculations reveal that the valence band is made up of the In-5 s and X-p orbitals, whereas conduction band is mostly made up of hybridization between the Sb-5p and X-p orbitals. According to optical properties, these four compounds have strong optical absorption in multi regions. When the number of halogen atoms increased, the absorption spectra shift from the ultraviolet region to the visible region. According to the examination of various optical parameters, Rb2InSbBr6 and Rb2InSbI6 exhibit greater light absorption than Rb2InSbF6 and Rb2InSbCl6 in the visible light range, making them suitable candidates for testing the high-power conversion efficiency and lead-free nature of solar cells.