Systematic study of optoelectronic and transport properties of cesium lead halide (Cs2PbX6; X = Cl, Br, I) double perovskites for solar cell applications

A systematic density functional theory investigation of Cs2PbX6 (X = Cl, Br, I) double perovskites is presented. The lattice constants are computed after structure optimization and using Birch-Murnaghan equations, which agree to the experimental literature. The mechanical stability conditions satisfy Born criteria, and the ductile nature is evidenced by the calculated Poisson's (v) and Pugh's ratios (B-0/G) because all three double perovskites exhibit values higher than the respective critical values v = 0.26 and B-0/G = 1.75. A detailed study of the optoelectronic properties reveals these double perovskites as promising candidates for future optical devices due to their direct band gaps (within 0.45-2.54 eV) and large absorption coefficients 5.95 x 10(5) cm(-1), which are suitable for solar cell applications. ZT calculations demonstrate minute variations within 200-800 K and computed parameter values are quite favorable for thermoelectric applications of these materials in the future. A p-type semiconducting nature is predicted by the computed thermoelectric properties. Additionally, computed refractive indices show Cs2PbBr6 and Cs2PbI6 exhibiting super-luminescent properties in the UV range. Therefore, the studied double perovskites provide further interest for future energy conversion and photonic based technologies.