TECHNOLOGY FOCUS - ELECTRONICS - Preferred Method: The method (M3) further involves depositing a semiconductor layer on the substrate.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The composition (C1) has atomic ratios of: X1 = Cu divide by Zn+Sn; X2 = Zn divide by Sn; X3 = Cu divide by S+Se; and X4 = 2(S+Se) divide by Cu+2Zn+4Sn (where X1, X2 and X4=1, greater than 1, or less than 1; X3=0.5). The composition is formulated as a nanoparticle ink solution suitable for forming a thin film coating on a substrate. The nanoparticle ink solution comprises a mixture of at least two different particles, including several first CZTSSe nanoparticle and a several a second particle (preferably second CZTSSe nanoparticle), where the first CZTSSe nanoparticle comprises first parameter value set defined by ya, X1a, X2a, X3a, and X4a, including a first parameter value; and the second CZTSSe nanoparticle comprises second parameter value set defined by yb, X1b, X2b, X3b, and X4b, including a second parameter value corresponding in type to the first value, where the first parameter value is different from second parameter value; and further a third parameter value defined by members of the first parameter value set, and the second CZTSSe nanoparticle comprises a fourth parameter value defined by the members of the second parameter value set, where the third and fourth parameter values correspond in type to one another, and the third parameter value is substantially the same as the fourth parameter value. The second particle comprises a CZTSSe family particle comprising Cu, Zn, Sn, S, and/or Se, and comprises a metal, metal alloy, oxide, sulfide, selenide, or telluride; a binary, ternary, quaternary, or higher chalcogenide particle of Cu, Zn, and/or Sn; or a CIGSSe nanoparticle (where CIGSSe nanoparticle has a chemical composition of formula Cu(In1-xGay)(S1-ySey) 2 (where x = 0-1), or a multinary IB-IIB/IIA-IVA-VIA type nanoparticle. The composition (C2) is formulated as a nanoparticle ink solution suitable for forming a thin film coating on a substrate. The nanoparticle ink solution comprises a mixture of at least two different pluralities of particles, including a several a first multinary IB-IIB/IIA-IVA-VIA nanoparticle and a several of second particle. The second particle comprises a second multinary IB-IIB/IIA-IVA-VIA nanoparticle, where the first and second multinary IB-IIB/IIA-IVA-VIA nanoparticles differ from one another in composition or stoichiometry; or the second particle comprises a CZTSSe nanoparticle, a CZTSSe family particle comprising Cu, Zn, Sn, S, and/or Se, or CIGSSe nanoparticle. Preferred Method: In the method (M1), the first and second sets of precursors are suspended in a single solvent to form a reaction mixture; or the method involves suspending the first set of precursors in a solvent to form a first precursor solution, suspending the second set of precursors in a solvent to form a second precursor solution, and combining the first and second precursor solutions to form a reaction mixture. The method (M1) further involves incubating the reaction mixture at 150-300 degrees C. The nanocrystals are collected by centrifugation following reaction of the precursors in the reaction mixture. The method (M2) further involves providing a source of at least one chalcogen and annealing the layer of the particles in the presence of the at least one chalcogen to form the CZTSSe thin film; depositing at least a second layer of particles on the substrate, where the second layer of particles comprises a several of second particle, and annealing the first and second layers of particles to form a CZTSSe thin film having a composition profile, where the first layer and/or second layer comprises several CZTSSe particles; or providing a source of at least one chalcogen, and annealing the first and second layers of particles in the presence of the at least one chalcogen to form the CZTSSe thin film having a composition profile. The first layer, and/or second layer is deposited on the substrate from at least one ink solution (preferably the first layer is deposited on the substrate from a first ink solution, and the second layer is deposited on the substrate from a second ink solution), where at least one of the ink solution(s) comprises an ink solution mixture including several first CZTSSe nanoparticles (I) and the second particles. In the method (M2), the layers of particles are deposited on the substrate by drop casting, spray coating, inkjet printing, roll coating, knife coating, spin coating, dip coating, and/or web coating; and after the deposition of any particle layer on the substrate, the particle layer is subjected to chemical treatment, heat treatment, etching, and/or washing. The annealing step involves gas phase chalcogen exchange reaction, or liquid phase chalcogen exchange reaction. The annealing is performed at 50-650 degrees C (preferably in a gas phase chalcogen exchange reaction at 350-550 degrees C, or in a liquid phase chalcogen exchange reaction at 200-350 degrees C). The particles of the method (M2) are selected to form a thin film coating where the overall composition of the thin film coating is substantially stoichiometric; or form a thin film coating where the overall composition of the thin film coating has an atomic ratio having a non-stoichiometric atomic ratio (where X1, X2 and X4 are greater than 1 or less than 1). Preferred Components: The substrate comprises glass, and/or metal. The first set of precursors comprises at least one member selected from elemental form, metal or metal alloy, metal salt of; and/or metal chalcogenide of Cu, Zn, and/or Sn. The second set of precursors comprises at least one member selected from elemental form and/or compound of S, and/or Se. The source of chalcogen of the method (M2) is selected from elemental chalcogen sources in vapor form, powder, flakes, or pellets; chalcogen compounds, including H2S, Na2S, Na2Se, H2Se, diethyl selenium, and their and gaseous derivatives; metal chalcogenides including sulfides, selenides, and tellurides including their binary, ternary, and quaternary compounds, selected from Cu2O, ZnO, Cu2S, Cu2Se, SnO, ZnS, Cu2SnS3, and Cu4SnS4; chalcogen-containing particles or particle layers including CZTSSe family particles, and CIGSSe nanoparticles; and/or chalcogen containing layers mixed with at least one elemental chalcogen source.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The first set of precursors comprises at least one member selected from organic complex of Cu, Zn, and/or Sn. The second set of precursors comprises at least one member selected from complex of S, and/or Se. The solvent comprises at least one alkane, alkenes, alkane derivative, and/or alkene derivative. The alkane or alkene derivative comprises at least one functional group selected from amine, carboxylic acid, ether, phosphine, phosphonic acid, and thiol. The source of chalcogen of the method (M2) is selected from thiourea, selenourea, and their gaseous derivatives; and/or chalcogen complexes including oleylamine-sulfur complex, trioctylphosphine-sulfur complex, and trioctylphosphine selenium complex.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The substrate comprises plastic. Preferred Definitions:    y=0 or 1.    EXAMPLE - Copper-tin-zinc-sulfur (CZTS) nanoparticle was performed by non-coordinating solvent as follows. Octadecene (10 ml) was combined with oleic acid (1.58 ml) to form a reconstituted solvent solution to which a mixture of copper(II) acetylacetonate (1 mmol; 99.99%), zinc acetylacetonate (0.5 mmol; 99.995%), and tin(IV) bis(acetylacetonate) dibromide (0.5 mmol; 98%) were added. The resulting precursor solution was added to a 100 ml three neck flask connected to a Schlenk line. The reaction products were heated to -130 degrees C under vacuum, degassed for 30 minutes, and purged with Ar several times. After raising the temperature to 230 degrees C, 1 M sulfur solution (in oleylamine, 2 ml) was injected through the third neck. Following injection, the reaction mixture was allowed to proceed for 30 minutes for completion. The heating mantle was then removed and the mixture was cooled to -80 degrees C. The resulting nanocrystals were collected by centrifugation in a 3:1 mixture of isopropanol and toluene. The precipitate was then redispersed in toluene (40 ml) to form a stable ink solution. The resulting CZTS nanocrystals were identified as Cu2.04\|0.25Zn0.89\|0.19Sn1.11\|0.05S4 by energy dispersive X-ray spectroscopy (EDX).