Effects of Moisture-Based Grain Boundary Passivation on Cell Performance and Ionic Migration in Organic–Inorganic Halide Perovskite Solar Cells

Because of the polycrystalline nature, grain boundaries (GBs) in hybrid perovskite thin films play critical roles in determining the charge collection efficiency of perovskite solar cells (PSCs), material stability, and in particular the ion migration, considering their relatively soft ionic bonds with low formation energy. Different GB passivation methods are being studied, and introducing PbI₂-rich phase at GBs in methylammonium lead iodide (MAPbI₃) has been found to be useful. In this study, combining macroscale measurements with tip-based microscopic probing that includes scanning Kelvin probe microscopy for surface potential mapping and conductive atomic force microscopy for charge transport mapping, we revealed the effects of PbI₂-rich phase at GBs, which was introduced in moisture-assisted synthesis of MAPbI₃ thin films. It was found that PbI₂ passivation of GBs could change the surface potential and charge carrier screening and significantly retard current conduction at the GB while enhancing conduction through the grain interior. Inhibition of ion migration at GBs, as well as enhanced PSC device performance, is reported.