Residual PbI₂ Conversion and Crystallization Control for Ambient‐Air Fabrication of Industrially Viable Perovskite Solar Cells

Abstract The fabrication of perovskite solar cells (PSCs) in the air can accelerate their industrialization. However, residual lead iodide (PbI₂) in perovskite films is considered a double‐edged sword. This study provides a comprehensive solution to this issue by introducing N, N‐methylenebisformamide (NMF) into the PbI₂ precursor solution. On the one hand, NMF molecules regulate the morphology and crystallization of PbI₂ films, creating sufficient space for the subsequent growth of perovskite films. On the other hand, NMF partially generates formamidinium (FA), which enables in situ conversion of residual PbI₂, transforming microcrystals and residual PbI₂ into high‐quality perovskite. Concurrently, NMF exhibits lattice compatibility with the perovskite and its presence at grain boundaries and interfaces effectively passivates undercoordinated lead ions in perovskite films. As a result, the optimized device achieves an efficiency of 24.87%, and the unencapsulated NMF‐optimized device retains 93.7% of its initial efficiency after 1680 h of storage in air, also exhibiting excellent thermal stability. This work demonstrates the effectiveness of using organic small molecules to simultaneously improve PbI₂ morphology and crystallinity, remove residual PbI₂, enhance perovskite crystallization, and passivate defects, enabling the fabrication of efficient and stable PSCs entirely under ambient conditions.