First Principles Study of the Properties of Cs2GaAgF6 Double Halide Perovskite Compound for Optoelectronic and Thermoelectric Applications

This study uses first-principles methods to analyze the structural, electronic, mechanical, thermophysical, optical, and thermoelectric properties of the Cs₂GaAgF₆ double-halide perovskite compound. The results have revealed that the Cs₂GaAgF₆ compound is mechanically and thermodynamically stable and can be potentially synthesized. The calculated band gap of the material was 2.27 eV, 2.41 eV, and 2.54 eV, derived from the local density approximation using Perdew–Zunger functional (LDA-PZ), the generalized gradient approximation using the Wu–Cohen (GGA-WC), and Perdew–Burke–Ernzerhof (GGA-PBE) functionals, respectively. The band gap was improved by using metaGGA functionals, which gave 3.10 eV, 3.15 eV, 3.15 eV, and 4.62 eV for strongly constrained and appropriately normed (SCAN), regularized strongly constrained and appropriately normed (rSCAN), restored-regularized strongly constrained and appropriately normed (r2SCAN), and Tran–Blaha-modified Becke–Johnson (TB-mBJ), respectively. The machine learning (ML) techniques predicted a band gap of 2.68 eV. The mechanical and elastic properties showed that the investigated compound is ductile and elastically anisotropic. Additionally, the optical properties showed excellent performance in the ultraviolet spectrum. Notably, the high absorption coefficients and optical conductivity values across the ultraviolet spectrum underscore the significant potential of the Cs₂GaAgF₆ double-halide perovskite compound for optoelectronic applications. Finally, the Cs₂GaAgF₆ double-halide perovskite compound showed a considerable figure of merit (ZT) value of 0.739 at approximately 600 K, suggesting its suitability for thermoelectric applications.