Tailored Crystallization and Defect Control via Acetamide Derivatives for Efficient Tin Perovskite Solar Cells

Tin perovskite solar cells (PSCs) have emerged as a highly promising lead-free alternative, attracting significant research interest owing to their reduced toxicity and excellent optoelectronic characteristics. However, their photovoltaic performance is severely restrained by the uncontrollable crystallization process and the resultant high defect density in the perovskite films. To address these issues, two acetamide derivatives, i.e., 2-cyanoacetamide (2CA) and 2-amino-2-cyanoacetamide (2A2CA), with multifunctional groups are used to improve the film quality of tin perovskites. Theoretical calculations and experimental results jointly demonstrate that 2A2CA molecules with larger dipole moments can significantly enhance the interaction between the carbonyl group and uncoordinatedSn²⁺ cations. The introduction of 2A2CA effectively increases the formation energy of tin vacancy defects (V_Sn), regulates the crystallization of tin perovskites, and produces high-quality tin perovskite films with smooth morphology, compact structure, increased crystallinity, and low defect density. Thereby, the 2A2CA-modified tin PSCs achieve a champion efficiency of 14.98% and maintain 90% after storing for over 2200 h in a nitrogen atmosphere.