Study of optical and thermoelectric properties of double perovskites Cs2KTlX6 (X = Cl, Br, I) for solar cell and energy harvesting

The double perovskites have emerging optical properties and extensively studied solar cells and renewable energy. In this work, we have investigated the optical, electronic and transport properties of Cs2KTlX6 (X = Cl, Br, I) using density functional theory. The thermodynamic stability is determined from the calculation of enthalpy of formation and structural stability is probed by computing the tolerance factor. Energy-volume optimization graphs reveal that lattice constant increased (11.31-12.80 angstrom) and bulk modulus decreased (20.46 15.90 GPa) with the increasing size of halogens. The optical properties are computed using TB-mBJ which reveals direct bandgaps (3.10, 2.0, 0.96) eV for (Cl, Br, I). In addition, the dielectric constant, refractive index, and reflectivity has been discussed in detail in the energy range of 0 6 eV. The absorption bands are recorded in infrared, visible and ultraviolet regions for Cl, Br and I based DPs. The temperature and chemical potential dependent transport properties are computed using BoltzTrap code. The appropriate values of thermoelectric parameters with high figure of merit at room temperature show the potential of these DPs for thermoelectric applications.