Selectively localized growth of two-dimensional perovskites at grain boundaries for efficient and stable CsPbI3 perovskite solar cells

All-inorganic CsPbI3 perovskite solar cells (PSCs) have garnered great interest in the photovoltaic field owing to their high thermal stability and application potential in tandem devices. However, their low operational stability remains a significant issue that limits their practical applications. This study proposes a novel strategy to simultaneously enhance the stability and performance of CsPbI3 PSCs by selectively-localizing growth of twodimensional (2D) perovskites at grain boundaries. The proposed strategy involves modifying CsPbI3 intermediate films with methylammonium chloride (MACl) and post-treating the CsPbI3 films with phenethylammonium chloride (PEACl). The former induces the formation of delta-phase species at grain boundaries, whereas the latter transforms them into a 2D perovskite in situ. These modifications introduce additional Cl- ions near the CsPbI3 surface, which along with the as-formed 2D perovskite significantly passivate surficial iodine vacancies (IV). This enhances the moisture resistivity of CsPbI3 films, improves the energy level alignment, and promotes carrier transport in PSCs. The optimized CsPbI3 PSC demonstrates a remarkable efficiency of 20.55% and exhibits exceptional long-term storage reliability and operational stability, retaining 95% of the initial efficiency after a 500 h test in ambient air.