Pressure effect on the halide double perovskite Cs2TlBiCl6; Ab initio study

Motivated by its potential solar cell applications, we investigated the mechanical, electronic, and optical properties of the double halide perovskite Cs2TlBiCl6 in the cubic Fm3m phase using first-principles calculations. The obtained lattice parameters of the cubic structure are in good agreement with previous results. The thermodynamic stability of the system from the cohesive energy and the formation energy. Also, from the elastic constants calculations, we confirmed the mechanical stability of this material for cubic symmetry. The calculated B/G ratio and Poisson's ratio show that the Cs2TlBiCl6 system has a ductile nature and strong ionic bonds. The TB-mBJ potential was used to calculate the electronic and optical properties. The Cs2TlBiCl6 system showed a direct band gap that is in the visible region but the absorption is weak in the same region. By applying pressure, we found an increase and shift in the absorption spectrum in the visible region. This finding indicates that the Cs2TlBiCl6 system can be considered as potential candidate for solar cell applications.