Structural and optical properties of vacancy-ordered double halide perovskites, Cs2TiI6 films

Vacancy-ordered double halide perovskites (DHP) structures have received considerable attention in photovoltaics due to their role in overcoming the lead toxicity issue for conventional halide perovskites. These materials also have tunable bandgaps and excellent optoelectronic properties suitable for a wide range of applications. Herein, we report the synthesis of titanium-based vacancy-ordered DHP, Cs2TiI6 using the Inverse Temperature Crystallization method for the first time. The Cs2TiI6 film's formation, structural and optical properties were also discussed. The films have a single-phase cubic structure with a space group of Fm3m (225) and a lattice parameter of 11.55 & ANGS;. The crystallite size, dislocation density, and micro-strain of Cs2TiI6 film calculated at (222) plane is 22 nm, 2.5 x 10-3 nm-2, and 0.53 x 10-3, respectively. Optical analysis reveals that Cs2TiI6 exhibits strong and wide optical absorption in the visible spectrum, with direct and indirect band gaps of 1.56 eV and 1.58 eV, respectively. The VESTA-calculated tolerance factor of 0.98 indicates excellent structural stability. These Titanium-based perovskites exhibit promising optoelectronic properties, opening the door for non-toxic perovskite devices with high performance and stability.