This study investigates the crystallization kinetics of perovskite films during gas-quenching-assisted blade coating using in situ optical spectroscopy and phase-field simulations. The research aims to optimize the crystallization process for high-quality, scalable perovskite solar cells. Gas quenching is shown to be critical in achieving a smooth, compact perovskite film by controlling nucleation rate. Excessive methylammonium iodide (MAI) in the precursor solution is found to increase grain size by accelerating crystal growth, leading to morphological variations. By balancing nucleation and growth rates with 5% excess MAI, high-quality perovskite films with low defect density are achieved. The study demonstrates that in situ optical spectroscopy combined with phase-field simulations provides insights into the role of gas quenching and non-stoichiometric precursors in perovskite crystallization. The results show that controlling the crystal growth rate is essential for achieving optimal film quality, leading to fully printed solar cells with a power conversion efficiency of 19.50% and mini solar modules with 15.28% efficiency. The findings highlight the importance of optimizing crystallization kinetics for efficient, scalable perovskite photovoltaics.This study investigates the crystallization kinetics of perovskite films during gas-quenching-assisted blade coating using in situ optical spectroscopy and phase-field simulations. The research aims to optimize the crystallization process for high-quality, scalable perovskite solar cells. Gas quenching is shown to be critical in achieving a smooth, compact perovskite film by controlling nucleation rate. Excessive methylammonium iodide (MAI) in the precursor solution is found to increase grain size by accelerating crystal growth, leading to morphological variations. By balancing nucleation and growth rates with 5% excess MAI, high-quality perovskite films with low defect density are achieved. The study demonstrates that in situ optical spectroscopy combined with phase-field simulations provides insights into the role of gas quenching and non-stoichiometric precursors in perovskite crystallization. The results show that controlling the crystal growth rate is essential for achieving optimal film quality, leading to fully printed solar cells with a power conversion efficiency of 19.50% and mini solar modules with 15.28% efficiency. The findings highlight the importance of optimizing crystallization kinetics for efficient, scalable perovskite photovoltaics.