An Emerging Stannous Fluoride Complex‐Enabled Highly Efficient Electron Collection and High Stability of Tin‐Based Perovskite Solar Cells

In advancing high‐performance tin‐based perovskite solar cells, rapid crystallization and oxidation susceptibility are key challenges. SnF₂, often added to control crystallization and oxidation, may impact cell performance, particularly postannealing. This study uses in situ variable‐temperature X‐Ray diffraction to examine SnF₂'s physicochemical behavior and phase transitions in these cells. The analysis highlights how residual SnF₂ affects carrier recombination through energy‐level structures. Postfilm formation, SnF₂ chemically interacts with 2,2′:6′,2″‐Terpyridine (TPY), forming a stannous fluoride complex that enhances electron transport and energy alignment. Crucially, TPY passivates surface defects and reduces tin vacancies, boosting device stability. The experimental results indicate that the unencapsulated devices in air atmosphere exhibit a stabilized power output retention rate above 90% of the initial efficiency after 29.5 h. After ≈800 h of continuous illumination in ambient air, the conversion efficiency can still be maintained above 100%. Remarkably, t₉₀ (time to retain 90% efficiency) of the target device in pure oxygen is over 24 h.