Moisture-Stable Intermediate Phase Manipulation for Efficient Perovskite Solar Cells Fabricated in Ambient Air

Fabricating high-efficiency perovskite solar cells (PSCs) in ambient air can facilitate their low-cost industrialization. However, the metastable wet-film stage before annealing during the film deposition process is susceptible to moisture invasion, making it difficult to form black-phase formamidinium lead iodide (α-FAPbI3) perovskites in ambient air. Herein, we construct a moisture-stable intermediate phase dominated by δ-FAPbI3 in the metastable wet-film stage using acetimidamidal acetate (AceAc). AceAc can induce the formation of δ-FAPbI3 to resist the invasion of moisture on a wet film, further transforming the formed δ-FAPbI3 into pure α-FAPbI3 in the presence of MACl. The resulting PSCs fabricated in ambient air achieve a power conversion efficiency (PCE) of 26.5% (certified at 25.9%) and maintain 98% of the initial PCE after 11000 h of aging under air conditions (25% relative humidity (RH) and 25 °C).