Developing a simple method to synthesize the perovskite layer without the antisolvent technique can facilitate the industrial production of perovskite solar cells (PSCs). Limited progress has been made for the antisolvent-free method on formamidinium lead triiodide perovskite layers because of the phase stability issue. Here, we use N-methyl pyrrolidone (NMP) as an additive to inhibit the nonperovskite phase of FAPbI 3 to fabricate the formamidinium iodide (FAI)−PbI 2 −NMP intermediate phase via the self-volatilization of volatile solvent 2-methoxyethanol instead of the traditional antisolvent method. The high-quality pure α phase of FAPbI 3 films is obtained by phase transition via annealing. The photovoltaic properties of the perovskite films affected by different NMP amounts are studied. The corresponding PSCs show a PCE of 20.1% compared to 15.6% for the PSCs fabricated with the classical antisolvent technique. The unencapsulated devices exhibit ∼75% efficiency of their initial PCE values after 35 days of storage. This method can be used in the scalable production of PSCs because of high reproducibility and easy operation.

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