Structural, Electronic and Optical studies of Pb-Free Halide Double Perovskite Cs2BiAgBr6; an mBJLDA approach

Despite phenomenal rise in the efficiency of hybrid halide perovskite, RPbX3 (R=organic group, X=Cl, Br, I) based solar cells from 3% to 22% in a time span of few years, the toxicity of lead (Pb) is one of the greatest challenges for their commercialization. This propelled the search for Pb-free materials with similar optoelectronic properties. In this regard, through first principles calculations, we have investigated the structural, electronic and optical properties of Pb-free halide double perovskites Cs2BiAgBr6 withinmBJLDA approach. The calculated bandgap of 2.01 eV is found to be in good agreement with the experimental value (2.19 eV). Our results exhibit that strong directional interaction between Ag-4d state with Br-4p states modifies the valence band leading to an indirect bandgap in Cs2BiAgBr6. The absorption onset in Cs2BiAgBr6 at 2.01 eV and bandgap is indirect in nature. The optical response of Cs2BiAgBr6 is comparable tocorresponding hybrid halide perovskites making it one suitable substitute for absorber layer in perovskite solar cells.