NOVELTY - Method-I of forming metal chalcogenide nanoparticles, comprises: contacting water, a source of zinc, a source of copper, optionally a source of tin and at least one of a source of sulfur and a source of selenium under conditions to produce a dispersion of the metal chalcogenide nanoparticles having a zinc chalcogenide distributed within its surface layer; and separating the metal chalcogenide nanoparticles from the dispersion.    USE - The method-I is useful for forming metal chalcogenide nanoparticles for forming the ink, where the ink is useful for fabricating kesterite film of a photovoltaic device (all claimed) e.g. high efficiency solar cell.    ADVANTAGE - The method easily forms the metal chalcogenide nanoparticles at high yield and purity without requiring organic compounds and heat treatment in an economical and environmental friendly manner. The ink fabricates the photovoltaic devices with high power conversion efficiency of greater than 6%.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a method-II for forming an ink for fabricating a kesterite film having a copper containing compound of formula (Cu2xZn1+ySn(S1zSez)4+q), comprising forming metal chalcogenide nanoparticles, and dispersing the metal chalcogenide nanoparticles in a solvent to form the ink, where the ink has a pH of 7-14;    (2) a method-III of forming the kesterite film comprising forming the ink by the method-II, depositing the ink onto a substrate to form a layer on the substrate, and heating the layer at a temperature and for a duration to form the kesterite film; and    (3) a photovoltaic device with power conversion efficiency of greater than 6%, comprising a substrate, a kesterite film absorber layer formed on the substrate by the method-III, an n-type semiconducting layer on the kesterite film, and a top electrode on the n-type semiconducting layer.    x, y = 0-1, preferably 0-0.5;    z = 0-1; and    q = -1 to 1, preferably -0.5 to 0.5.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a method for forming a kesterite film.    Extracting solid product comprising chalcogenide nanoparticles by filtration or centrifugation (110)    Optionally, washing extracted nanoparticles with clean solvent (112)    Redispersing nanoparticles in solvent with optional additives (126)    Depositing nanoparticle dispersion to form film on a substrate (128)    Optionally, drying the film. (130)