Exploring the structural, electronic and optical properties of vacancy-ordered double perovskites Cs2TlAsX6 (X = I, Br, Cl) based on first-principles

In this work, we have been systematically studied the structural stability, electronic and optical properties of Cs2TlAsX6 (X = I, Br, Cl) by adopting first-principles calculations based on density functional theory (DFT). The mechanical and thermodynamic stability of Cs2TlAsX6 are confirmed by the calculated elastic constants, negative binding energies and formation energies. The calculated Pugh and Poisson's ratio indicate that Cs2TlAsI6 is brittle, and Cs2TlAsBr6 and Cs2TlAsCl6 are ductile. Moreover, the calculated results reveal that Cs2TlAsX6 (X = I, Br, Cl) are direct bandgap semiconductors with values of 1.476 eV, 1.874 eV, and 2.19 eV, respectively. Furthermore, the effective mass of electrons of Cs2TlAsX6 is much smaller than that of many perovskite materials. In addition, all the materials exhibit significant absorption capacity of visible and near ultraviolet light. Perovskite Cs2TlAsX6 is very suitable for solar cell applications and other optoelectronic devices because of its good light absorption performance and narrow band gap.