Effective perovskite crystallization control strategies for flexible substrates with scalable processing techniques have rarely been reported and remain an important challenge. In this study, 3-mercaptobenzoic acid (3-MBA) was introduced into the perovskite precursor to modulate the crystallization dynamics, facilitating rapid nucleation while slowing down crystal growth. This approach enabled the formation of uniform, dense large-area perovskite films on flexible substrates. Consequently, a$12\ \text{cm}^{2}$flexible perovskite solar module achieved a power conversion efficiency (PCE) of 16.43%. Additionally, the module exhibited enhanced mechanical stability under various bending radii and improved light stability, marking a substantial advance toward the practical application of flexible perovskite solar modules.