First principle study of structural, mechanical, electronic and optical properties of K2TiX6 (X=Cl, Br, I) for photovoltaic applications

In this present work, we have uncovered the structural stability, mechanical, electronic and optical properties of earth-abundant titanium based vacancy ordered double perovskites K2TiX6 (X = Cl, Br, I) through the density functional theory. The material's thermal stabilities are calculated from the formation energies; K2TiCl6 is the most thermally stable material among K2TiX6 (X = Cl, Br, I). The calculated structures are in the cubic phase with the Fm-3m space group, and the lattice parameters are in strong agreement with reported values. All the double perovskites are classified as ductile materials and are mechanically stable. The perovskites' band gaps are varied in the range of 3.18 eV-1.54 eV by the anion replacement from Cl to I. Total density and partial density of states readily explore the intention of band gap variations. The optical properties are calculated from the frequencydependent dielectric functions. The optical absorption is high for K2TiBr6 and K2TiI6 in the visible region of 400-800 nm. Comprehensive results disclose that K2TiBr6 is the most noticeable material for photovoltaic and optoelectronic applications.