Optoelectronic properties of all-Inorganic lead-free halide double perovskites (RbxCs1-x)2AgBiBr6 for solar cell applications

Abstract

Solar cells based on lead-free double perovskites as absorber layer is an environment friendly, stable alternative for the conventional lead based hybrid halide perovskites. A comprehensive theoretical study on the optical and electronic properties of all-inorganic double perovskite with A₂BB’X₆ stoichiometry is done using density functional theory. Doping studies on (Rb_xCs_1-x )₂AgBiBr₆ perovskite is done using the virtual crystal approximation method within density functional theory. It is found that as increasing the Rb content (x) from 0.0 to 1.0 in Rb_xCs_1-xAgBiBr₆, the lattice parameter, dielectric constant and band gap are found to be decreasing linearly in accordance with Vegard's law. The lattice constant decreases linearly in x with a function of a(x) = 11.516 - 0.0057 x (Å), while the band gap decreases linearly as a function of x, E_g(x) = 1.472 - 0.0009 x (eV). Opto-electronic properties of substitutional doping of Rb in (Rb_xCs_1-x)₂AgBiBr₆ is compared with Cs₂AgBiX₆ (X=Cl, Br, I) and Br doped Cs₂AgIn(Br_xCl_1-x)₆.