Effect of Precursor Aging on Built-In Potential in Formamidinium-Based Perovskite Solar Cells

Formamidinium-based perovskite with optimal bandgap and improved thermal stability is a promising active material for application in perovskite solar cells (PSCs). The hybrid precursor solutions, formed by adding various smaller cations, are often used for improving the phase stability in PSCs. Herein, research to understand the aging effect of a methylammonium- and bromine-free formamidinium precursor solution on the performance of FA_0.85Cs_0.1Rb_0.05PbI₃-based PSCs is reported. The results reveal that deterioration in the built-in potential in the PSCs is closely associated with the formation of the secondary phase in the FA_0.85Cs_0.1Rb_0.05PbI₃ active layer. The formation of the secondary phase in the active layer is related to the hydrolysis of the precursor solution. The suppression of the moisture encroachment greatly enhances the durability of the precursor solution and performance reproducibility of PSCs.