Optimizing UV Resistance and Defect Passivation in Perovskite Solar Cells with Tailored Tin Oxide

Abstract Tin oxide (SnO₂) as an electron transport layer (ETL) has garnered significant attention in planar perovskite solar cells (PSCs) for its excellent physical and chemical properties, paving its commercial potential. However, its drawbacks, such as surface defects and photocatalytic properties due to its wide band gap, remain unresolved. Under ultraviolet (UV) light, photocatalytic SnO₂ induces perovskite phase transitions at the interface, compromising device stability. In this study, the fluorescent dopant sodium 2,2′‐([1,1′‐Biphenyl]‐4,4′‐Diylbis (Ethene‐2,1‐Diyl)) Dibenzenesulfonate (CF351) is introduced into SnO₂ Solution for the first time. With excellent UV absorption, CF351 effectively blocks UV light, reducing SnO₂‐induced perovskite degradation. Perovskite films on CF351‐doped SnO₂ show remarkable stability under continuous UV irradiation (365 nm) for 32 days, the resistance to phase transition is improved by 100%. PSCs retaining 80.8% of their initial power conversion efficiency (PCE) after ≈1000 h of UV exposure, compared to only 18.7% for control. Additionally, CF351 passivates interfacial defects, regulates crystallization, and optimizes energy levels. It's down‐conversion capability also enhances photocurrent by generating extra visible photons. As a result, CF351‐doped PSCs achieve a PCE of 22.59%, significantly surpassing the 20.42% of control devices. This work provides an effective strategy for preparing highly efficient and UV stable PSCs.