Intrinsic Defects of Vacancy-Ordered Perovskite Cs2TiIBr5for Solar Cells

Vacancy-ordered perovskites A2M4+X6have shown potential in luminescence and photocatalytic applications, while limited research on them for solar cells exists. Previous studies have demonstrated that Cs2TiI6and Cs2TiBr6possess 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–xand further conducted a comprehensive analysis of the intrinsic defect properties and structural stability of Cs2TiIBr5and Cs2TiI2Br4. We find that as-yet-unsynthesized Cs2TiIBr5has a direct bandgap of 1.39 eV. Additionally, our results reveal that Cs2TiIBr5is thermodynamically stable and exhibits good defect tolerance. Notably, Cs2TiIBr5is 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.