Process-Dependent Performance of FAMAPbI₃ Perovskite Solar Cells Fabricated by One-Step and Two-Step Methods

A comprehensive comparison was conducted between formamidinium–methylammonium lead iodide (FAMAPbI₃) 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 FAMAPbI₃ films and provide valuable insights into process–structure–property relationships for scalable, high-efficiency PSCs.