TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Nanoparticle: The CIS comprising nanoparticle comprises Cu, In, and Se with a secondary phase comprising copper selenide (CuSe), CuSe2, Cu3Se2, or any combination, where the CuSe is alpha -CuSe, beta -CuSe, or gamma -CuSe. The CIS comprising nanoparticle has a cubic (spharelite) or tetragonal (chalcopyrite) CIS crystal lattice. The CIS crystal lattice comprises Cu, In, and Se where a portion of In is substituted with Al, Zn, Sn, Ga, or any combination, and/or Cu is substituted with Au, Ag, or any combination in the cation lattice. The CIS crystal lattice comprises Cu, In, and Se where a portion of its anion lattice is substituted with S and/or Te, The CIS crystal lattice forms a solid solution comprising Al, Zn, Au, Sn, Ga, Ag or any combination, or forms a solid solution comprising sulfur or tellurium. The CIS comprising nanoparticle is 10-500 nm in cross section. The distribution of cross sections is narrow or monodispersed. Preferred Method: In preparing the CIS comprising nanoparticle, the copper halide is copper(I) chloride (CuCl), copper(I) bromide (CuBr), copper(I) iodide (CuI), copper(II) chloride (CuCl2), copper(II) bromide (CuBr2), copper(II) iodide (CuI2), Cu2Cl2, Cu3Cl3 Cu2Br2, Cu3Br3, Cu2I2, Cu3I3, CuOC(O)CH3, Cu(OC(O)CH3)2, Cu2(OC(O)CH3)2, Cu3(OC(O)CH3)3, or any combination. The indium halide is indium chloride (InCl), InCl2, InCl3, indium iodide (InI), InI2, InI3, indium bromide (InBr), InBr2, InBr3, InOC(O)CH3, In(OC(O)CH3)2, In(OC(O)CH3)3, or any combination. The solvent for the first solution and second solution independently comprise methanol, ethanol, 3-8C alcohol, or any combination. The solvent for the third solution comprises isopropyl amine, isobutyl amine, butyl amine, methylamine, ethylamine, ethylenediamine, other 3-8C amine, 3-8C diamine, or any combination. Heating comprises refluxing in the solvents of the combined solutions. Washing is performed with methanol or any volatile alcohol. The method further comprises drying the CIS comprising nanoparticles, where drying is performed under vacuum. In preparing the CIS comprising absorber layer, forming is spray coating, drop casting, screen printing, or inkjet printing. The annealing occurs at a maximum temperature of about 380 degrees C or 280 degrees C. Preferred Ink: In the ink, the solvent is an alcohol or a sulfoxide. The CIS comprising nanoparticles comprises a blend of CIS comprising nanoparticles having different sizes, shapes or elemental composition. Preferred Layer: In the CIS comprising absorber layer, the microstructure further comprises columnar grains. Preferred Device: The photovoltaic device further comprises a metallic or polymeric substrate, where the substrate is stainless steel or a polyimide.