Fluorocarbon Surfactant‐Assisted Large‐Area Uniform and Water‐Resistant Perovskite Films for Efficient Photovoltaics

Formamidinium (FA)‐based lead triiodide perovskites are suitable light‐absorbing materials for solar cells due to their narrow bandgap, long‐range charge diffusion length, and excellent thermal stability. However, large‐area uniformity and phase purity are still challenging issues in the two‐step solution processed perovskite films because of the incomplete spreading/reacting of the organic amine salt solution. Herein, a novel multifunctional nonionic fluorocarbon surfactant (FS) is introduced to improve the crystallization of perovskites via the strategy of reducing the surface tension of the organic amine salt solution and facilitating the adequate binding of the organic amine salts with PbI 2 . Moreover, the FS additives effectively reduce residual PbI 2 ; passivate the surface and interfacial defects of perovskites. The FS modified perovskite solar cells (PSCs) exhibit a champion power conversion efficiency (PCE) of 21.72% (0.16 cm 2 ) with an enhanced stability, and the unencapsulated device maintains about 80% of the initial PCE even after 1000 h of storage. In addition, the larger PSCs with the active area of 1.00 cm 2 deliver a peak PCE of 19.19%. Eventually, FS impedes moisture intrusion and effectively mitigates the decomposition of perovskite film. This work opens the way to explore large‐area PSCs with high performance and long‐term stability.