Tuning of band gap by anion variation of Ga₂TiX₆(X = Cl, Br, I) for solar cells and renewable energy

Vacancy-ordered double perovskites have been studied vastly for energy applications for the last few decades. In this article, we have investigated the optical and thermoelectric characteristics of Ga2TiX6 (X = Cl, Br, I). The phonons dispersions, formation energy, and tolerance factors reveal dynamic and structural stabilities. The predicted band gaps turn out to be 2.74 eV, 2.0 eV, and 1.32 eV for Ga2TiCl6, Ga2TiBr6, and Ga2TiI6, respectively, corresponding to the absorption bands 275 nm to 413 nm, 365 nm to 539 nm, and 413 nm to 689 nm. Therefore, the absorption band in the entire visible region for Ga2TiI6 makes it an excellent material for solar cells. The optical characteristics are explained by dielectric constants (ϵ 1, ϵ 2), absorption coefficient, and dielectric constants. Thermoelectric efficiency is addressed by calculating the figure of merit to highlight the potential of the investigated materials for thermoelectric applications.