NOVELTY - Aqueous solutions of combined cationic precursor of copper sulfate, zinc sulfate, and tin sulfate with different molarities and cationic pH in acidic range, and anionic precursor of thioacetamide with molarities of 0.1-0.4 and acidic pH, are prepared. A substrate is immersed for 10-40 seconds in the aqueous solutions and rinsed for 10-40 seconds to form an adherent copper-zinc-tin sulfide thin film on the substrate surface. The film is annealed at sufficient temperature in air to obtain a polycrystalline copper-zinc-tin sulfide thin film.    USE - Production of polycrystalline copper-zinc-tin sulfide thin film on large-area (greater than 10 cm2) glass substrates of thin-film solar cells.    ADVANTAGE - The method enables simple and economical production of high-quality, uniform polycrystalline copper-zinc-tin sulfide thin films having excellent optical property and electrical property, with convenient and controlled large-area deposition at room temperature. The method does not require sophisticated instrumentation like vacuum system and other controlling expensive equipment. Since the operating temperature is low, energy is saved and corrosion/oxidation of metallic substrate by high temperature is prevented. Unlike in electrodeposition, electroconductivity of substrate is not an essential requirement. Any type of substrate, such as metals, semiconductors or insulators of complex shape can be used.    DETAILED DESCRIPTION - Aqueous solutions of combined cationic precursor of copper sulfate, zinc sulfate, and tin sulfate with different molarities and cationic pH in acidic range, and anionic precursor of thioacetamide with molarities of 0.1-0.4 and acidic pH, are prepared. A substrate having an area of greater than 10 cm2 is immersed for 10-40 seconds in the aqueous solutions and rinsed for 10-40 seconds in cycle number sufficient to form an adherent copper-zinc-tin sulfide (Cu2ZnSnS4) thin film on the substrate surface. The film is annealed at sufficient temperature in air to obtain a polycrystalline copper-zinc-tin sulfide thin film.