Green Precursor Aqueous Solution for High-Performance Cu(In,Ga)(S,Se) ₂ Thin-Film Solar Cells

Cu(In,Ga)(S,Se)₂ (CIGSSe) thin-film solar cells have emerged as one of the most promising next-generation photovoltaic technologies, owing to their record power conversion efficiency (PCE) exceeding 23%, tunable bandgap, and outstanding environmental stability. Although solution-based deposition of CIGSSe absorber layer offers substantial cost and processing advantages over vacuum-based methods, conventional solution-processed methods suffer from critical limitations, including the toxicity of organic solvents and detrimental carbon residue contamination. To address these challenges, we developed a green, facile, and cost-effective aqueous solution for fabricating high-performance CIGSSe thin-film solar cells. Our approach utilizes an environmentally benign, odorless precursor solution prepared by dissolving copper oxide, silver oxide, indium hydroxide, gallium nitrate, and thiourea (TU) in a carbon-free sulfamic acid (H₂NSO₃H) aqueous solution. The aqueous precursor exhibits excellent wettability on Mo-coated soda-lime glass (Mo-SLG), as evidenced by a low contact angle of 36.70°, ensuring uniform film formation. The resulting CIGSSe solar cells achieve a champion PCE of 14.04%, with a short-circuit current density (<i>J</i>_sc) of 35.42 mA/cm², an open-circuit voltage (<i>V</i>_oc) of 0.61 V, and a fill factor (FF) of 65.00%. This water-based processing route not only eliminates toxic and hazardous organic solvents but also reduces manufacturing costs compared with conventional methods, representing a significant advancement toward sustainable and scalable photovoltaic production.