Environmentally Friendly R2R Process for Flexible Perovskite Solar Cells via DMF ‐Free Cosolvent Ink

Roll‐to‐roll (R2R) coating is an essential manufacturing strategy for the scalable production of perovskite solar cells (PSCs), offering high throughput and compatibility with flexible substrates. However, the widespread use of toxic solvents such as dimethylformamide (DMF) in the perovskite precursor solution poses significant environmental and health concerns, particularly in large‐scale continuous processing. In this study, we propose solutions using a DMF‐free, environmentally friendly solvent system using a cosolvent mixture of dimethyl sulfoxide (DMSO) and acetonitrile (ACN) for the fabrication of R2R‐processed PSCs via a two‐step slot‐die coating method. DMSO provides high solubility for lead iodide (PbI 2 ) due to its strong coordination ability and ACN promotes rapid drying thanks to its high volatility, enabling the formation of uniform PbI 2 layers. Also, the large volatility difference between ACN and DMSO induced porous PbI 2 structures during drying, which facilitated the infiltration of the formamidinium (FAI) solution and enhanced the conversion to high‐quality perovskite layers. This led to improved crystallinity and grain growth, ultimately resulting in a power conversion efficiency of 15.84% for flexible small‐area devices (0.125 cm 2 ). Our results demonstrate a realistic pathway toward toxic‐solvent‐free, scalable PSC manufacturing and highlight the potential of this green R2R process for future commercialization of perovskite photovoltaics.