NOVELTY - Method for forming a thin film of copper-zinc-tin containing compound, comprises (a) forming a dispersion (110) comprising copper containing nanoparticles (101), zinc containing nanoparticles (103) and tin containing nanoparticles in a dispersing agent, (b) depositing the dispersion on a substrate (109) to form a precursor thin film (120), and (c) heating the substrate comprising the precursor thin film in an inert atmosphere at a temperature of 300-600 degrees C to form the thin film of copper-zinc-tin containing compound.    USE - The method is useful for forming the thin film of copper-zinc-tin containing compound, which is useful in a solar cell device (all claimed).    ADVANTAGE - The method simply and economically provides the thin film with mass production and low cost solution deposition techniques under ambient conditions with less energy consumption and without forming any toxic byproduct in an environmentally friendly manner.    DETAILED DESCRIPTION - Method for forming a thin film of copper-zinc-tin containing compound of formula (Cu-Zn-Sn-X) (I), comprises (a) forming a dispersion (110) comprising copper containing nanoparticles (101) of formula ((Cu)pX) (II), zinc containing nanoparticles (103) of formula (ZnX) (III) and tin containing nanoparticles of formula (SnXq) (IV) in a dispersing agent, (b) depositing the dispersion on a substrate (109) to form a precursor thin film (120), and (c) heating the substrate comprising the precursor thin film in an inert atmosphere at a temperature of 300-600 degrees C to form the thin film of (I).    X = selenium (preferred) and/or sulfur;    p = 1-2; and    q = 1-2.    An INDEPENDENT CLAIM is included for a Cu-Zn-Sn-X thin film formed by the method.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a method for forming a thin film of copper-zinc-tin containing compound.    Copper containing nanoparticles (101)    Zinc containing nanoparticles (103)    Substrate (109)    Dispersion (110)    Precursor thin film. (120)