Thin-film CuIn(Se,S)2 (i.e., CIS) absorbers have been solution-deposited using a hydrazine-based approach that offers the potential to significantly lower the fabrication cost for CIS solar cells. In this method,metal chalcogenides are completely dissolved in hydrazine, forming a homogeneous precursor solution. Film deposition is demonstrated by spin-coating of the precursor solution onto various substrates, including Mo-coated glass and thermally oxidized silicon wafers. Using this approach, no postdeposition anneal in a toxic Se or S-containing environment is needed to obtainCIS films. Instead, only a simple heat-treatment in an inert atmosphere is required, resulting in CIS films with good crystallinity. Bandgap tuning can readily be achieved by varying the amount of S incorporated into the film. Complete CIS devices with glass/Mo/CIS/CdS/i-ZnO/ITO structure are fabricated using absorbers produced via this hydrazine-based approach. Air Mass 1.5G power conversion efficiencies of as high as 12.2% have been achieved, demonstrating that this new approach has great potential as a low-cost alternative for high-efficiency CIS solar cell production.