Investigation on electronic structure and optical properties of lead-free double perovskite A2SnCl6 (A= Sr, K) from first principle study

The double perovskite materials A₂SnCl₆ (A= Sr, K) demonstrate significantly enhanced stability compared to Sn²⁺ based perovskites, as well as promising optoelectronic properties including direct bandgaps. A₂SnCl₆ adopts a vacancy-ordered double perovskite structure featuring isolated [SnCl₆] octahedra, which contribute to a quantum confinement effect that enhances photoluminescence. The calculated structures exhibit a cubic phase with the Fm-3m space group, and their lattice parameters agree closely with reported values. All double perovskites exhibit mechanical stability. The band gaps of the perovskites vary depending on the A substitution from K to Sr. The total density and partial density of states provide insights into the variations in band gaps. The optical properties are determined through frequency-dependent dielectric functions, with optical absorption occurring in the visible range of 400-800 nm. Considering the stability, bandgap, and optical absorption properties, A₂SnCl₆ (A= Sr, K) emerges as a potential material for photovoltaic applications.