A first-principles study on the optoelectronic properties of mixed-halide double perovskites Cs₂TiI_6-xBr_x

All-inorganic double perovskites as promising photovoltaic materials have received great attention in recent years. In this work, the structural, mechanical, electronic, and optical properties of mixed-halide double perovskites Cs₂TiI_6-xBr_x (x = 0, 2, 4, and 6) were studied by using first-principles calculations. The calculated lattice parameters of Cs₂TiI_6-xBr_x agree well with the reported experimental values. The calculated results have confirmed that these compounds are thermodynamically stable. Moreover, these mixed-halide double perovskites can easily be converted into thin films based on their unique mechanical properties. The obtained band gaps of the Cs₂TiI_6-xBr_x systems using the PBE+U method have better matched with the experimental values. When the Br content increases, the band gap of Cs₂TiI_6-xBr_x increases gradually, which leads to a decreased optical performance in the visible light region. Based on a suitable direct band gap and strong absorption coefficient, Cs₂TiI₂Br₄ is an ideal potential material for single-junction solar cells