NOVELTY - The precursor layer is formed on surface of substrate (101) using precursor material comprising group IB chalcogenide and/or group IIIA chalcogenide particles. The particle precursor material is heated to melt particles and to release excess amount of chalcogen from chalcogenide particles. The excess amount of chalcogen attains liquid form and acts as flux to form group IB and IIIA chalcogenide film (108) at desired stoichiometric ratio. The overall amount of chalcogen in precursor material is more than or equal to stoichiometric amount in chalcogenide film.    USE - For forming precursor layer used in semiconductor thin film used for fabrication of solar cell.    ADVANTAGE - The precursor material fabricates high quality uniform film rapidly and economically at low temperature.    DETAILED DESCRIPTION - The precursor layer is formed on the surface of a substrate using a precursor material comprising group IB chalcogenide and/or group IIIA chalcogenide particles in amount more than overall amount of chalcogen in group IB and group IIIA chalcogenide film formed from the precursor material. The particle precursor material is heated at temperature sufficient to melt the particles and to release excess amount of chalcogen from the chalcogenide particles. The excess amount of chalcogen attains liquid form and acts as a flux to improve intermixing of elements to form group IB and group IIIA chalcogenide film at desired stoichiometric ratio. The overall amount of chalcogen in the precursor material is more than or equal to stoichiometric amount in chalcogenide film. The particles are chalcogen-rich particles, preferably selenium-rich particles, sulfur-rich particles and/or tellurium-rich particles. The group IB element is copper. The group IIIA element comprises gallium, indium and/or aluminum. The chalcogen is selenium, sulfur or tellurium. The particles are alloy particles, preferably binary alloy particles, ternary alloy particles or multi-nary alloy particles, compound particles, or solid-solution particles. The solid-solution comprises copper, indium, gallium, selenium, copper-indium, copper-gallium, indium-gallium, sodium, sodium compound, sodium fluoride, sodium-indium sulfide, copper selenide, copper sulfide, indium selenide, indium sulfide, gallium selenide, gallium sulfide, copper-indium selenide, copper-indium sulfide, copper-gallium selenide, copper-gallium sulfide, indium-gallium selenide, indium-gallium sulfide, copper-indium-gallium selenide, and/or copper-indium-gallium sulfide. The substrate is a rigid substrate, and comprises material chosen from glass, soda-lime glass, steel, stainless steel, aluminum, polymer and/or ceramic.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic diagram of the formation of chalcogenide film from binary nanoparticles and chalcogen particles.    Substrate (101)    Chalcogenide film (108)