NOVELTY - Depositing a kesterite film comprising tin selenide compounds, comprises: contacting a hydrazine-based solvent with a source of copper, a source of tin, a source of zinc carboxylate, a source of at least one of sulfur and selenium under conditions sufficient to form a solution substantially free of solid particles; applying the solution onto a substrate to form a thin layer; and annealing the thin layer at a temperature, pressure, and length of time sufficient to form the kesterite film.    USE - The method is useful for depositing a kesterite film onto a substrate such as plastic, metal foil, glass, ceramics, aluminum foil coated with a layer of molybdenum and/or a polymer, where the kesterite film is useful in photovoltaic device (all claimed).    ADVANTAGE - The method is capable of economically depositing the kesterite film onto the substrate in an eco-friendly manner.    DETAILED DESCRIPTION - Depositing a kesterite film comprising tin selenide compounds of formula (Cu2-xZn1+ySn(S1-zSez)4+q), comprises: contacting a hydrazine-based solvent with a source of copper, a source of tin, a source of zinc carboxylate, a source of at least one of sulfur and selenium under conditions sufficient to form a solution substantially free of solid particles; applying the solution onto a substrate to form a thin layer; and annealing the thin layer at a temperature, pressure, and length of time sufficient to form the kesterite film.    x-z = 0-1, where x and y are preferably 0-0.5; and    q = -1 to 1, preferably -0.5 to 0.5.    INDEPENDENT CLAIMS are included for:    (1) a photovoltaic device comprising a top electrode having transparent conductive material, an n-type semiconducting layer, the kesterite film on the substrate formed by the method, and a substrate having an electrically conductive surface; and    (2) a hydrazine-based precursor solution for forming the kesterite film, comprising a source of copper, a source of tin, a source of zinc carboxylate, a source of at least one of sulfur and selenium, and hydrazine, where a dispersion of the zinc carboxylate in hydrazine is mixed with a solution comprising hydrazine and the source of tin to solubilize and stabilize the source of the zinc carboxylate.