Defects Mitigation and Charge Transport Promotion via a Multifunctional Lewis Base for Efficient 2D/3D Tin Perovskite Solar Cells

Tin perovskite solar cells (PSCs) have garnered considerable attention as promising alternatives to lead PSCs due to their lower toxicity and outstanding optoelectronic properties. However, their efficiency and stability, particularly in 2D/3D tin PSCs, are usually hindered by high defect densities and inefficient carrier transport. In this study, a small-molecule Lewis base with multiple functional groups-cyanoacetohydrazide (CAH) is employed to mitigate defects and enhance charge transport in 2D/3D tin PSCs. It is revealed that the carbonyl, amine, and cyano groups in CAH form strong chemical bonds with Sn²⁺ ions, resulting in synergetic coordination effects. Moreover, the strong interaction between CAH and tin perovskite effectively regulates the crystallization process of perovskite film, resulting in a high-quality tin perovskite film with enhanced crystallinity, reduced defect density, and a modulated 2D/3D phase distribution. As a result, the optimized 2D/3D tin PSCs achieve a remarkable power conversion efficiency of 15.06%, marking one of the highest values for 2D/3D tin PSCs. Furthermore, the optimized devices exhibit outstanding stability, retaining 95% of their initial performance after 2000 h of storage in a nitrogen atmosphere.