NOVELTY - A copper indium diselenide (CIS) comprising nanoparticle comprises: copper (Cu), where optionally Cu includes some gold (Au), silver (Ag) or both; indium (In), aluminum (Al), zinc (Zn), tin (Sn), gallium (Ga), or any combination; and selenium (Se), sulfur (S), tellurium (Te) or any combination., where the nanoparticle further comprises a secondary phase that comprises a compound that decomposes to a liquid, is free of a surfactant or binding agent.    USE - The CIS comprising nanoparticle is useful for producing an ink, where the ink can be used for screen or inkjet printing a precursor layer that can be annealed to a CIS comprising absorber layer for a photovoltaic device (all claimed).    ADVANTAGE - The CIS comprising nanoparticle is free of surfactants or binding agents, displays a narrow size distribution and is 30-500 nm in cross section.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are:    (1) a method to prepare the CIS comprising nanoparticle, comprising: providing a copper halide or its equivalent in a first solution; providing an indium halide or its equivalent in a second solution; providing selenium or sulfur in a third solution; combining the first solution with the second solution and the third solution; heating the combined solution to a temperature up to 150 degrees C to form a precipitate; and optionally, washing the precipitated CIS comprising nanoparticles, where no surfactant or binding agent is included in any solution;    (2) an ink comprising the CIS comprising nanoparticles and one or more solvent;    (3) a method of preparing a CIS comprising absorber layer, comprising: forming a layer of ink on a surface; removing the solvent from the ink to form a precursor layer; and annealing the precursor layer under an overgas of selenium or sulfur to form the CIS comprising absorber layer;    (4) a CIS comprising absorber layer, comprising copper indium diselenide (CuInSe2) with a microstructure comprising lamellar grains; and    (5) a photovoltaic device comprising the CIS comprising absorber layer.