First-principles study of halide double perovskite Cs₂SnX₆ (X ¼ Cl, Br, I) for solar cell applications

In this work, we used di®erent approximations, namely the GGA and LDA of the density functional theory framework, to investigate the properties of the double perovskite Cs₂SnX₆ (X ¼ Cl, Br, I). We found that these materials are mechanically stable, and the calculated band gaps are 3.62 eV for Cs₂SnCl₆, 2.33 eV for Cs₂SnBr₆, and 1.00 eV for Cs₂SnI₆, which agree well with the experimental results. The band structure reveals that the conduction band primarily arises from hybridization between the Sn-5s orbitals and the halogen p orbitals, while the valence band is predominantly composed of the halogen p orbitals. Additionally, we observed that all Cs₂SnX₆ compounds exhibit strong optical absorption in the ultraviolet region. Moreover, the absorption spectra edges shift toward the red from Cs₂SnCl₆ to Cs₂SnI₆. The thermoelectric properties have also been extensively characterized in this study. These favorable physical characteristics make Cs₂SnX₆ compounds attractive candidates for replacing expensive silicon cells in solar panels.