Density functional theory study of structural, electronic, optical, mechanical, and thermodynamic properties of halide double perovskites Cs2AgBiX6 (X = Cl, Br, I) for photovoltaic applications

In recent years, double perovskite materials have been considered potential candidates for different applications. Therefore, in this study, we investigated the structural, electronic, optical, and mechanical properties of Cs2AgBiX6 (X = Cl, Br, I) double perovskite materials based on first-principles calculations. All properties were evaluated using the LDA + U technique in the CASTEP code. According to the values of the octahedral factor and tolerance factor, Cs2AgBiX6 (X = Cl, Br, I) possesses a cubic structure with the space group Fm3m (225). The lattice constants were evaluated as 7.7579 & ANGS;, 8.1264 & ANGS;, and 8.6814 & ANGS; for Cs2AgBiCl6, Cs2AgBiBr6, and Cs2AgBiI6, respectively. The tolerance factor and octahedral factor confirmed their structural stability. The electronic properties indicate that the double perovskite materials are semiconductors. The energy band gaps were calculated as 2.02 eV, 1.53 eV, and 1.00 eV for Cs2AgBiCl6, Cs2AgBiBr6, and Cs2AgBiI6, respectively. The optical properties of Cs2AgBiX6 (X = Cl, Br, I) were calculated and discussed in the photon energy range of 0-25 eV to explain the interaction between light and matter. Assessment of the mechanical properties showed that the materials are ductile in nature. The theoretical power conversion efficiencies were calculated as 21.74%, 30.95%, and 30.03% for Cs2AgBiCl6, Cs2AgBiBr6, and Cs2AgBiI6, respectively. Our analysis of the electronic and optical properties demonstrates that these double perovskite materials are suitable for photovoltaic and optoelectronics applications.