The development of efficient, scalable, and low-cost photovoltaic technologies is critical for advancing global energy sustainability. Perovskite solar cells (PSCs) have emerged as promising alternatives to traditional single-junction silicon-based solar cells due to their high power conversion efficiency (PCE) and solution-processable active materials. However, conventional fabrication methods typically require inert environments and complex anti-solvent processes, which increase production costs and limit scalability. Sequential deposition offers a promising solution by decoupling the solidification and crystallization steps, thereby eliminating the need for anti-solvent processes. Despite these advantages, fabricating high-quality mixed-cation perovskite layers in air remains a significant challenge, primarily due to the sensitivity of perovskite materials to moisture, which disrupts phase stability and perovskite phase formation. In this study, we addressed these challenges by developing an air-processable perovskite layer using a sequential deposition process. To overcome moisture-induced issues, pre-heating the substrate was employed to reduce surface tension and improve film coverage. Furthermore, imidazole iodide (ImI) was introduced into the PbI₂ precursor to effectively cap Pb sites, preventing moisture interference and promoting a complete transition to the α-phase of formamidinium lead iodide (FAPbI₃​) without residual PbI₂ in air​. These strategies enabled the production of PSCs in air achieving a champion PCE of 18.73%. Stability testing further demonstrated that PSCs incorporating ImI exhibited a T₈₀​ device lifetime exceeding 500 hours. The finding demonstrates its role in moisture prevention and durability enhancement for the air-processable perovskite solar cells.