NOVELTY - Copper indium gallium diselenide/disulfide (CIGS) nanoparticles are prepared by heating (102) copper salt together with greater than or equal to 1 salt selected from indium salt and gallium salt in solvent at 1st temperature to produce reaction solution, adding (104) organo-chalcogen precursor to reaction solution, heating (106) reaction solution to 2nd temperature while stirring for 1st time interval, cooling (110) reaction solution to room temperature, and isolating (112) nanoparticles from reaction solution.    USE - Preparation of copper indium gallium diselenide/disulfide nanoparticles for copper indium gallium diselenide/disulfide-based photovoltaic device (claimed).    ADVANTAGE - The nanoparticles are processable in organic solvents and enable fabrication of photovoltaic device at low cost.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) copper indium gallium diselenide/disulfide (CIGS) nanoparticles; and    (2) CIGS-based photovoltaic device prepared by performing step (a) of mixing nanoparticles in solvent to form ink, performing step (b) of depositing ink on substrate to form film, performing step (c) of annealing film in inert atmosphere to produce annealed film, performing step (d) of repeating steps (b) and (c) until annealed film obtains a preselected thickness, performing step (e) of depositing n-type semiconductor layer on annealed film to form junction, performing step (f) of depositing intrinsic zinc oxide (ZnO) on junction to form extended depletion layer, performing step (g) of depositing window layer on extended depletion layer, performing step (h) of depositing metal grid on window layer to form assembly, and performing step (i) of encapsulating assembly to form photovoltaic device.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart of the process of preparing copper-rich CIGS nanoparticles.    Heating process at 1st temperature (102)    Addition process of organo-chalcogen precursor (104)    Heating process at 2nd temperature (106)    Cooling process of reaction solution (110)    Isolation process of nanoparticles (112)