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.