Eco‐Friendly Solvent System for Inkjet Deposition of Wide Bandgap Perovskite Solar Cells Enabling Tandem Integration

ABSTRACT Inkjet printing offers scalable, material‐efficient route to fabricate perovskite solar cells. However, the widespread use of toxic and hazardous solvents in one‐step printed perovskite absorber layers poses significant environmental and safety challenges when handling large volumes in production. In this work, we overcome this limitation by demonstrating high‐performance, wide‐bandgap inkjet‐printed perovskite solar cells processed with truly green, non‐toxic solvent system, entirely free of carcinogenic and highly hazardous components. γ‐Valerolactone, a biomass‐derived solvent, is employed as the primary solvent due to its low toxicity and environmental impact, and dimethyl sulfoxide is introduced as a co‐solvent to overcome solubility constraints of wide‐bandgap perovskite precursors (> 1.68 eV). The ink chemistry and rheology are optimized for solubility and printability. The challenges of wetting and drying dynamics are addressed by tuning interactions between substrate and ink, combined with additive and surface engineering to enhance performance. The resulting green‐solvent‐based, inkjet‐printed perovskite solar cells exhibit power conversion efficiencies exceeding 17% in single‐junction devices. Critically, we further demonstrate first perovskite/silicon tandem solar cell integrating one‐step inkjet‐printed perovskite thin film, achieving an efficiency above 28%. These results establish green solvent inkjet printing as a viable and compelling pathway toward sustainable and scalable manufacturing of high‐efficiency perovskite photovoltaics.