Structure, electronic and optical properties of Cs2Ti(Br1-xYx)6 (Y = Cl, I; x = 0, 0.25, 0.5, 0.75, 1) perovskites: The first principles investigations

Extensive studies have demonstrated that all-inorganic lead-free halide perovskite solar cells as promising photoelectric devices are receiving great attention. In this paper, we have investigated the structures, electronical and optical properties of perovskite Cs2Ti(Br1-xYx)6 (Y = Cl, I, x ​= ​0, 0.25, 0.5, 0.75, 1). When x ​= ​0.25, the system Cs2Ti(Br0.75Cl0.25)6 has the suitable band gap value. With the increase of Cl content, the absorption coefficients showing blue shift which lead to the optical performance slightly decreased. But the systems become more stable. For the substitution of I to Br, the band gap values are lower than the optimal one. As to optical calculations, we find that the systems show obvious red shift, which result in the optical performance enhanced. However, the systems become unstable and not easy to be prepared. All calculations reveal that these excellent properties make Cs2Ti(Br0.75Cl0.25)6 as an ideal candidate material for perovskite solar cells.