First principle study of Lead free halide double perovskites Cs2AuBiX6 (X = Cl, Br)

Abstract

Halide double perovskites based on bismuth and silver have recently been studied extensively as potential environment friendly alternatives to lead-based hybrid halide perovskites. In this paper the structural, electronic and optical properties of Pb-free halide double perovskites Cs2AuBiX6 were investigated. The material was systematically analyzed within the framework of Density Functional Theory (DFT) using various exchange correlation such as LDA, PBE and PBE-sol. The optimized lattice parameters are found to be 10.94 Å and 11.45 Å for Cl and Br respectively in the face-centered cubic structure (Fm3̅m space group). It is found that these compounds have an indirect band gap. As the halogens are changed from Chlorine to Bromine the band gap is decreasing and first-principles calculations indicate that the energy gaps values are 0.63 eV and 0.24 eV respectively. This energy might be slightly underestimated as expected from DFT calculations. Optical studies make it clear that the compound shows good absorbance in visible region. The optical properties of Cs2AuBiX6 is comparable to hybrid halide perovskites MAPbI3 and halide double perovskites (like Cs2AgBiBr6) making it a suitable candidate for absorber layer in perovskite solar cells.