Intrinsic Defects of Vacancy-Ordered Perovskite Cs₂TiIBr₅ for Solar Cells

Abstract

Vacancy-ordered perovskites A 2 M 4+ X 6 have shown potential in luminescence and photocatalytic applications, while limited research on them for solar cells exists. Previous studies have demonstrated that Cs 2 TiI 6 and Cs 2 TiBr 6 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 Cs 2 TiI x Br 6−x and further conducted a comprehensive analysis of the intrinsic defect properties and structural stability of Cs 2 TiIBr 5 and Cs 2 TiI 2 Br 4 . We find that as-yet-unsynthesized Cs 2 TiIBr 5 has a direct bandgap of 1.39 eV. Additionally, our results reveal that Cs 2 TiIBr 5 is thermodynamically stable and exhibits good defect tolerance. Notably, Cs 2 TiIBr 5 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.