Computational Study of Lead-Free Halide Double Perovskites 𝟐 𝟔 Structural, optical and Electronic Properties from DFT Calculations

Abstract

This thesis presents a theoretical study of the structural, electronic, and optical properties of the lead-free halide double perovskites K₂AgSbCl₆ and K₂CuSbCl₆. The calculations were performed within the framework of Density Functional Theory (DFT) using the GGA-PBE approximation, employing the CASTEP code. The results show that both compounds crystallize in a cubic double perovskite structure (space group Fm3􀴥 m and are geometrically stable. Band structure analysis reveals that K₂AgSbCl₆ possesses an indirect band gap of approximately 1.327 eV, while K₂CuSbCl₆ exhibits a narrower band gap of about 0.646 eV. Substituting silver with copper significantly reduces the band gap and enhances optical activity in the low-energy region. Both materials exhibit strong optical absorption and significant dielectric response, making them promising candidates for optoelectronic and photovoltaic applications