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 <em>A₂BB&rsquo;X₆ </em>stoichiometry is done using density functional theory. Doping studies on (<em>Rb_xCs_1-x)₂AgBiBr₆</em>perovskite is done using the virtual crystal approximation method within density functional theory. It is found that as increasing the Rb content (<em>x)</em> from 0.0 to 1.0 in <em>Rb_xCs_1-xAgBiBr₆</em>, 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 <em>x</em> with a function of <em>a(x) = 11.516 - 0.0057 x</em> (Å), while the band gap decreases linearly as a function of <em>x, E_g(x) = 1.472 - 0.0009 x </em>(eV). Opto-electronic properties of substitutional doping of Rb in (<em>Rb_xCs_1-x)₂AgBiBr₆</em> is compared with <em>Cs₂AgBiX₆ (X=Cl, Br, I) </em>and <em>Br</em> doped <em>Cs₂AgIn(Br_xCl_1-x)₆</em>.