Fine optimized cation immobilization strategy for enhancing stability and efficiency of perovskite solar cells

The migration and volatilization of cations within organic–inorganic hybrid perovskite (OIPs) materials has been identified as a major issue for irreversibly degrading perovskite solar cells (PSCs), severely limiting their performance and impeding progress toward large-scale applications. To mitigate these problems, an adjustable cation immobilization strategy was proposed for the first time, in which a series of fluorobenzenesulfonamide (FBSA) molecules was introduced into perovskite precursor, a strong coordination bond was formed between the sulfonamide group with the octahedral imperfection caused by iodine vacancy, along with a hydrogen bond formed between the cation and F atom. As a result, the A-site cations were tightly immobilized in the octahedral of perovskite crystal lattice and the uncoordinated Pb2+ defects were effectively eliminated. Besides, the immobilization distance of cation was finely optimized by changing the substitution position of F atoms. Based on the cation-immobilized perovskite film, the efficiency of PSCs was significantly increased from 19.88 % to 22.30 %. Moreover, the unencapsulated PSCs exhibited impressive light and thermal stability, retaining 82 % of the initial efficiency after 720 h illumination at 1-sun, and maintaining nearly 80 % of the initial PCE after heating at 85 °C for 240 h. Thus, the present study offers a promising approach for advancing the commercialization of stable and high-efficiency perovskite solar cells.