The study investigates the crystallization kinetics of perovskite films during gas-quenching-assisted blade coating, a scalable method for fabricating perovskite photovoltaics. In situ optical spectroscopies, integrated into a doctor-blading setup, reveal that gas quenching significantly enhances film quality by controlling the nucleation rate, resulting in a smooth and compact perovskite layer. Phase-field simulations and experimental results show that excessive methylammonium iodide (MAI) in the precursor solution accelerates crystal growth, leading to larger grain sizes. Optimal film quality is achieved with a 5% excess of MAI, resulting in fully printed solar cells with a champion power conversion efficiency (PCE) of 19.50% and mini solar modules with a PCE of 15.28%. The study highlights the importance of balancing nucleation and growth rates to optimize film properties and device performance.The study investigates the crystallization kinetics of perovskite films during gas-quenching-assisted blade coating, a scalable method for fabricating perovskite photovoltaics. In situ optical spectroscopies, integrated into a doctor-blading setup, reveal that gas quenching significantly enhances film quality by controlling the nucleation rate, resulting in a smooth and compact perovskite layer. Phase-field simulations and experimental results show that excessive methylammonium iodide (MAI) in the precursor solution accelerates crystal growth, leading to larger grain sizes. Optimal film quality is achieved with a 5% excess of MAI, resulting in fully printed solar cells with a champion power conversion efficiency (PCE) of 19.50% and mini solar modules with a PCE of 15.28%. The study highlights the importance of balancing nucleation and growth rates to optimize film properties and device performance.