“…The degradation of PSCs is mainly attributed to the hybrid ionic nature of perovskite materials, which is intrinsically unstable in the presence of moisture, oxygen, heat and light. − In addition, inhomogeneity of polycrystalline perovskite films due to imperfect stoichiometric ratios, nonequilibrium reactions, and partial evaporation of the organic components also deteriorates the long-term stability of PSCs . For instance, state-of-the-art PSCs have typically utilized excess lead iodide (PbI 2 ) (5–10 mol %) in the precursor solution to prepare polycrystalline perovskite films. , This is due to the fact that a slight excess of PbI 2 at the perovskite grain boundaries (GBs) and surfaces has some benefits for high efficiency PSCs, including defect passivation, reduction of halide vacancy concentration, and enhancement of carrier lifetime. − However, excess PbI 2 can be a double-edged sword for PSCs. , Numerous publications have reported that excess PbI 2 readily decomposes to gaseous I 2 and metallic Pb 0 under light and thermal stress, acting as catalytic sites to trigger perovskite decomposition. − It is therefore necessary to manage the unstable PbI 2 in perovskite films to achieve an efficient and stable PSC.…”