Mechanism-guided design and process optimization of a roll-to-sheet coating system for flexible perovskite solar cells

We report a mechanism-informed roll-to-sheet (R2S) slot-die coating system engineered for high-uniformity deposition on large-area flexible substrates, advancing scalable fabrication of perovskite solar cells (PSCs). Unlike conventional post-deposition thermal treatments, which induce secondary fluid flow and result in pinholes, thickness non-uniformity, and compromised interfacial contact, our R2S platform integrates an in-line heated roller that delivers precise thermal energy during coating. This real-time thermal input governs solvent evaporation kinetics and crystallization pathways, minimizing defect formation at the wet-to-dry transition stage. Guided by a detailed understanding of solvent drying dynamics and their influence on film morphology, we optimized critical parameters, including roller temperature, rotation speed, and solution flow rate, to achieve highly uniform and pinhole-free active layers. Devices fabricated with two R2S-coated functional layers exhibited a power conversion efficiency (PCE) of 12.58 %, while triple-layer R2S devices reached 11.58 %, approaching the 13.24 % PCE benchmark of spin-coated controls. Notably, the integrated heated roller not only accelerates drying but also enhances film adhesion and crystallinity, enabling reproducible multi-layer stacking with superior mechanical integrity. This scalable R2S approach bridges the gap between lab-scale coating and industrial roll-to-roll production, laying essential groundwork for future high-throughput manufacturing of flexible PSCs.