Non-aliphatic Protic Ammonia for Post Healing of Formamidinium-containing Perovskite Films

Abstract The solvents employed for perovskite materials not only play roles in dissolving the precursors but also participate in crystallization process. The high boiling point aprotic solvents with O-donor coordinating ligands have been extensively studied, but a highly uniform film still requires the participation of additives or an additional step to accelerate the nucle-ation rate. The volatile protic aliphatic amines with both coordinating ligands and hydrogen proton facilitate the pro-cessing of pure MAPbX3 perovskite films with higher crystallinity, fewer defects, and easier for large scale fabrication as well. However, their attempts in FA-containing perovskite is challenged heretofore. Here, the degradation mechanism of FA-containing perovskite in aliphatic amines environment has been revealed, and non-aliphatic ammonia was selected to avoid undesired side reactions. In particular, low temperature is proved to be crucial to enable FAPbI3 perovskite material absorb enough NH3 molecules to form a flowable intermediate state, which is the heart for defect healing. As a result, a rough FA-containing perovskite film was effectively healed to a highly uniform, compact one, toward an efficiency of 23.3% with excellent reproducibility. The manipulating of the interaction between perovskite and ammonia opens up a new di-rection for upscaling the fabrication of highly efficient FA-containing perovskite solar cells.