Despite the rapid development of small‐area perovskite solar cells (PSCs), the performance limitations of large‐area perovskite solar modules (PSMs) hinder their commercialization. Uncontrolled crystallization kinetics and complex environmental factors in scalable manufacturing pose major challenges in regulating perovskite crystallization, ultimately deteriorating film quality. Herein, mercaptoacetamide (MAA) is introduced as a dual‐function additive, improving perovskite crystal homogeneity while efficiently passivating defects through multifaceted interactions with perovskite constituents. The delayed crystallization rate broadens the processing window of perovskite films, significantly increasing grain size and improving crystal orientation. In addition, MAA's ability to reduce vacancy defects and its strong reducibility effectively shield perovskite films from hydrolysis and oxidation in ambient air, facilitating the fabrication of high‐quality, large‐area perovskite films. Based on this strategy, power conversion efficiencies (PCEs) of 25.52%, 22.87%, and 20.18% are achieved on PSCs with an active area of 0.09 cm2, and mini‐modules with aperture areas of 11.09 and 113.00 cm2, respectively, all fabricated using a scalable deposition method. Meanwhile, the encapsulated target devices demonstrated excellent photothermal and damp‐heat stability.