Process‐Dependent Performance of FAMAPbI ₃ Perovskite Solar Cells Fabricated by One‐Step and Two‐Step Methods

A comprehensive comparison was conducted between formamidinium–methylammonium lead iodide (FAMAPbI 3 ) perovskite solar cells (PSCs) fabricated using an optimized one‐step process in a glovebox and a two‐step method under ambient air to identify the key factors governing performance and stability. Systematic optimization of processing parameters revealed that the one‐step films exhibited smaller grains, higher defect densities, and greater moisture sensitivity, which promotes trap‐assisted recombination and reduces stability. In contrast, the two‐step films contained larger and better‐connected crystalline domains, enhanced crystallinity, and lower trap densities, resulting in stronger light absorption and more efficient charge transport. Optical and electrical analyses, including steady‐state photoluminescence (PL), time‐resolved photoluminescence (TRPL), dark current, and space‐charge‐limited current (SCLC) measurements, confirmed longer carrier lifetimes, suppressed nonradiative recombination, and reduced deep‐trap density in the two‐step films. The champion two‐step PSC achieved a power conversion efficiency of 21.34%, outperforming the one‐step device (18.90%). Despite exhibiting higher hysteresis associated with stronger ion migration, the two‐step method demonstrated good reproducibility and retained 83% of its initial efficiency, compared with the one‐step device, after 500 h of continuous illumination. These results indicate the effectiveness of the ambient‐air two‐step route in producing good quality FAMAPbI 3 films and provide valuable insights into process–structure–property relationships for scalable, high‐efficiency PSCs.