Achieving Defect Passivation and Oriented Crystallization Regulation at the SnO ₂ /Perovskite Interface via Molecular Bridging

Buried interface defects between the SnO₂ electron transport layer (ETL) and the perovskite layer severely limit the efficiency, hysteresis, and stability of SnO₂-based perovskite solar cells (PSCs). In this study, 3-Isothioureidopropionic acid (ATPN) is introduced as a molecular bridge at the buried perovskite interface, effectively passivating interface defects and regulating the oriented growth of perovskite crystals. The carboxyl (-COOH) groups of ATPN passivate dangling Sn bonds on SnO₂, reducing surface oxygen vacancies and facilitating charge extraction and transport. Meanwhile, the imino (-C═NH) and amino (-NH₂) groups of ATPN effectively passivate undercoordinated Pb²⁺ and I^- ions in the perovskite, reducing interfacial defects and optimizing energy level alignment. In situ crystallization studies reveal that ATPN-mediated modulation extends the recrystallization process of the perovskite, promoting the formation of larger grains during fabrication. Additionally, this strategy induces a highly preferred out-of-plane (100) crystal orientation by eliminating energy barriers, thus enhancing carrier extraction and transport. A champion ATPN-treated PSC achieved a power conversion efficiency (PCE) of 24.06%, compared to 22.15% for the control device. After 1920 h of aging in a nitrogen atmosphere, the ATPN-modified device retained 90.14% of its initial PCE, while the unmodified device retained only 68.32%.