NOVELTY - The method comprises coating (104) a substrate containing elemental copper, indium and gallium with a solution comprising a source of selenium (Se) dissolved in a solvent to form a layer comprising Se on the substrate, where a thickness or composition of the Se layer is determined during the coating step by measuring thickness of the solution, concentration of Se in the solution, viscosity of the solution and/or speed of coating the solution on the substrate, and heating (106) the coated substrate. The step of coating is performed by ink jet coating or ink-jet printing and spraying process.    USE - The method is useful for selenization in the formation of a copper indium gallium diselenide (CIGS) layer in a photovoltaic (PV) device (claimed) such as a solar cell, which is useful for commercial markets including residential rooftops, commercial rooftops, utility-scale PV projects, building integrated PV and building applied PV applications.    ADVANTAGE - The method allows economical and efficient selenization of the CIGS layer with less material consumption, increased reliability and high stability in a safe manner thus enhancing life span of the PV device.    DETAILED DESCRIPTION - The method comprises coating (104) a substrate containing elemental copper, indium and gallium with a solution comprising a source of selenium (Se) dissolved in a solvent to form a layer comprising Se on the substrate, where a thickness or composition of the Se layer is determined during the coating step by measuring thickness of the solution, concentration of Se in the solution, viscosity of the solution and/or speed of coating the solution on the substrate, and heating (106) the coated substrate. The step of coating is performed by ink jet coating or ink-jet printing and spraying process. The concentration of selenium in the solvent is 0.1-5 M. The heating step is carried out in an inert environment at a temperature of 200-650 degrees C for 1-300 minutes. An INDEPENDENT CLAIM is included for a method for forming a copper indium gallium diselenide layer on a substrate.    DESCRIPTION OF DRAWING(S) - The figure shows a flowchart of a method for selenization in the formation of a copper indium gallium diselenide layer.    Depositing elemental copper, indium and gallium onto a substrate (102)    Coating a substrate with a solution comprising a source of selenium (104)    Heating the coated substrate. (106)