Defect Passivation on SnO2/Perovskite Interface Using Oxalate-Based Passivators for Efficient and Stable Perovskite Solar Cells

Tin oxide (SnO 2 ) is a popular electron transport layer (ETL) in n-i-p structured perovskite solar cells, with its excellent charge mobility and longer chemical stability. However, Interfacial defects at the SnO 2 /perovskite interface are still a major bottleneck limiting the efficiency and stability of perovskite solar cells (PSCs). Herein, we introduced lithium difluoro(oxalato)borate (LiDFOB) and lithium bis(oxalato)borate (LiBOB) as interfacial modifiers to regulate the SnO 2 /perovskite interface and control perovskite crystallization, resulting in larger grain sizes and reduced grain boundaries. Spectroscopic analysis confirms strong interfacial interactions and effective defect passivation at both the electron transport layer and the buried perovskite interface, leading to reduced trap density and suppressed metallic Pb formation. The resulting films exhibit lower trap density and suppressed nonradiative recombination, which are reflected in improved charge transport, reduced leakage current, and enhanced conductivity. Consequently, the optimized devices achieve a champion power conversion efficiency of 25.12%, significantly higher than the control (23.42%), along with excellent operational stability, retaining 98% and 95% of initial efficiency under ambient and thermal (85 °C) conditions over 2000 h. This work demonstrates an effective strategy for simultaneously optimizing interfacial chemistry and film quality to achieve highly efficient and stable perovskite solar cells (PSCs).