Metallic Lead Formation in Perovskites: Mechanisms, Suppression, and Future Directions

Lead halide perovskites APbX₃ (A = methylammonium, formamidinium, cesium; X = halogen) have advanced the field of optoelectronics, particularly in solar cells, photodetectors, and light-emitting diodes, due to their outstanding properties. However, a significant challenge remains unresolved: the formation of metallic lead (Pb⁰), which introduces deep-level defects that trap charge carriers and degrade device performance. The formation of Pb⁰ in perovskites can occur after their synthesis under various conditions, including high-energy radiation, light, heat, and moisture, and has also been observed during perovskite crystallization. Thus, it is crucial to understand the underlying mechanisms of Pb⁰ formation and its suppression pathways. Recent studies have explored various strategies to suppress Pb⁰ formation, including compositional engineering, additive incorporation, and protective passivation layers. In this review, we discuss the origins of Pb⁰ formation in perovskites, focusing on the mechanisms driving this process under different environmental conditions, and then strategies for suppressing Pb⁰ formation, including compositional engineering and passivation techniques. By addressing these aspects, we seek to identify pathways for enhancing the stability and performance of perovskite-based devices, enabling their widespread adoption in commercial applications.