Moisture-inhibited deprotonation at the buried interface enables efficient perovskite solar cells with a high fill factor of over 86%

SnO2 is one of the best electron-transport materials for perovskite solar cells (PSCs). However, the limited interfacial contact and the reaction occurring at the buried interface between the perovskite and SnO2 reduce their performance. Herein, we revealed a strong deprotonation reaction of formamidinium cation that occurred at the buried interface during perovskite growth under a nitrogen atmosphere. In contrast, this reaction was considerably inhibited by moisture when the perovskite was grown under an ambient atmosphere (Amb-perovskite). Thus, defects at the buried interface of the Amb-perovskite were reduced, considerably suppressing the non-radiative recombination. Amb-PSC resulted in an efficiency of 25.69%, with an ultra-high fill factor of 86.21% and enhanced operational stability without decay after more than 1000 h under continuous 1-sun illumination. This work provides an efficient strategy for perovskite film annealing under an ambient atmosphere to minimise the buried interface loss. Its scaling-up potential and easy-processibility make it a promising strategy for low-cost large-scale manufacturing of PSCs.