Giant‐Domain Perovskite Films via Reduced‐Temperature Meniscus‐Guided Coating: Fluid‐Dynamic Control of Supersaturation

Scalable fabrication of high‐quality perovskite films is critical for the industrialization of perovskite solar cells (PSCs). Meniscus‐guided coating is promising, yet the trade‐off between maintaining liquid film continuity and securing the time window for crystal growth remains a significant bottleneck. Here, we demonstrate a strategy to achieve both full coverage and giant domains (>3 × 10 −2 mm 2 ) via reduced‐temperature (100°C) bar‐coating. By integrating in situ microscopy with fluid dynamics analysis, we reveal that a specific low‐speed condition (0.3 mm s −1 ) within the evaporation regime maintains the solution in a metastable supersaturation zone. Our analysis identifies that the circulation loop formed by the interaction of Couette and Marangoni flows not only continuously supplies solute to the meniscus tip but also suppresses excessive evaporation through advective cooling. This fluid‐dynamic regulation prevents explosive nucleation while circumventing the film rupture (dewetting) often observed in slow drying, enabling the formation of continuous films with giant crystal domains. Consequently, PSCs utilizing these giant‐domain films achieved a power conversion efficiency of 16.5%, significantly outperforming devices with smaller crystal domains. This study provides a physical framework linking macroscopic coating parameters to microscopic crystallization dynamics, offering a rational pathway for scalable, high‐performance device manufacturing.