Intrinsic Defects of Vacancy-Ordered Perovskite Cs₂TiIBr₅ for Solar Cells

Vacancy-ordered perovskites A2M4+X6 have shown potential in luminescence and photocatalytic applications, while limited research on them for solar cells exists. Previous studies have demonstrated that Cs2TiI6 and Cs2TiBr6 possess good stability and high optical absorption coefficients in the visible light range but have undesirable bandgap characteristics. In response to the shortcoming, we investigated the bandgap properties of Cs2TiIxBr6–x and further conducted a comprehensive analysis of the intrinsic defect properties and structural stability of Cs2TiIBr5 and Cs2TiI2Br4. We find that as-yet-unsynthesized Cs2TiIBr5 has a direct bandgap of 1.39 eV. Additionally, our results reveal that Cs2TiIBr5 is thermodynamically stable and exhibits good defect tolerance. Notably, Cs2TiIBr5 is expected to exhibit n-type conductivity with a considerable concentration of charge carriers under Ti-rich/Cs-rich/I-poor chemical potential conditions. Overall, our findings provide valuable theoretical insights that facilitate the experimental synthesis of new vacancy-ordered perovskites.