We report an approach for the fabrication of CuIn(S,Se)2-based photovoltaic devices from hydrazinium precursors in non-hydrazine solvents, specifically a ethanolamine/dimethyl sulfoxide (EA/DMSO) mixture. For the first time, both Cu hydrazinium precursor and Cu-In hydrazinium precursor are found with good solubility in non-hydrazine solvents, producing molecular-level blending of metal precursors. Sulfur loss in Cu hydrazinium precursor is compensated for by either introduction of excessive S/Se or the formation of S/Se-bridged Cu-In compounds. The success of dissolving Cu-In hydrazinium precursor is ascribed to the coordinated S group and strong intramolecular interaction within non-hydrazine solvents. X-ray diffraction (XRD) and Raman characterization indicate the formation of the CuIn(S,Se)2 phase after annealing. Through introducing different amounts of excess S/Se, the ratio between CuInS2 and CuInSe2, as well as the morphology of the resulted CuIn(S,Se)2 film can be controlled. Optimized devices exhibit a power conversion efficiency of 3.8% with a CISS absorber layer of only around 300 nm thickness, which is comparable to N2H4-based devices of similar thickness.