First-principles study of halide double perovskite Cs₂SnX₆ (X=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.