TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: In the method (M1): each of the first and second layers comprises several particles, where at least one element in the chemical composition denoted by Cu((In)1-x1(Ga)x1)((S)1-y1(Se)y1)2, is substituted by an element selected from Ag, Au, Al, Tl, O, and Te. The method (M1) involves: depositing a first layer of particles comprising several CIGSSe particles having a chemical composition denoted by Cu((In)1-x2(Ga)x1)((S)1-y1(Se)y1)2 on a substrate; depositing a second layer of particles comprising a CIGSSe particles having a chemical composition denoted by Cu((In)1-x2(Ga)x2)((S)1-y2(Se)y2)2; a CIGSSe family particle containing at least one element from the group of Cu, In, Ga, S, and Se; and annealing individually or in combination one or both of the first and second layers of particles to form a CIGSSe thin film having a composition profile along the depth of the film. The second layer of particles comprises several CIGSSe particles having a chemical composition denoted by Cu((In)1-x2(Ga)x2)((S)1-y2(Se)y2)2. The second layer of particles comprises several CIGSSe family particles containing at least one element from the group consisting of Cu, In, Ga, S, and Se. The method (M1) further involves: depositing a portion of particles comprising several third particles. Depositing the portion of particles involves dispersing the third particle within one or both of the first and second layers to form at least one mixed layer of particles. Depositing the portion of particles involves depositing third particles on the substrate to form a third layer of particles. The third particle comprises a CIGSSe particle denoted as Cu((In)1-x3(Ga)x3)((S)1-y3(Se)y3)2. The third particle comprises a CIGSSe family particle comprising at least one element selected from Cu, In, Ga, S, and Se. The CIGSSe family particle comprises a metal oxide or mixed metal oxide particle comprising at least one of Cu, In, or Ga; or comprises a chalcogenide compound containing at least one of Cu, In, or Ga. The chalcogenide compound includes at least one of S, Se, Te, or O. The particles of the first, second, and third layers are about less than or equal to 50 nm in size. After 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 is carried out after deposition of each particle-based layer. The annealing involves heating in an inert, reducing, and/or oxidizing atmosphere. The annealing involves: (i) heating in an Se containing atmosphere, where the Se containing atmosphere comprises a source of Se selected from H2Se, Se vapor, Se-containing compounds, Se pellets, Se powders, Se particles within the particle-based layers, at least one Se layer on the particle-based layers, and/or a Se coating on at least one of the particles; and/or (ii) heating in an S containing atmosphere, where the S containing atmosphere comprises a source of S selected from H2S, S vapor, S containing compounds, S pellets, S powders, S particles within the particle-based layers, at least one S layer on the particle-based layers, and/or S coating on at least one of the particles. The method further involves: forming a CIGSSe absorber film on the substrate prior to forming the first layer. The CIGSSe absorber film is formed using a deposition method selected from vacuum co-evaporation, sputtering, selenization of various precursor layers, electrodeposition, and spray pyrolysis. The CIGSSe absorber film is porous or nonporous. Forming the first and second layers of particles entails depositing an ink solution comprising particles. The ink solution is deposited by a solution-based technique selected from drop casting, spray coating, inkjet printing, roll coating, knife coating, spin coating, dip coating, and/or web coating. The method further involves etching at least one of the first, second layers, and third layers. The etching is carried out with an aqueous solution comprising potassium cyanide; and is carried out after or before annealing. The method (M1) for forming a CIGSSe thin film involves: providing a substrate having an absorber formed on it; depositing a layer of particles on the absorber to form a composite precursor film, the layer of particles comprising CIGSSe particles having a chemical composition denoted by Cu((In)1-x1(Ga)x1)((S)1-y1(Se)y1)2; and annealing the composite precursor film to form a CIGSSe thin film having a composition profile along the depth of the film. The method further involves depositing a semiconductor layer on the substrate. In the method (M3): the metal chalcogenide particles comprise at least one element from each of Groups IB, IIIA, and VIA of the Periodic Table, and the elements from Groups IB, IIIA, and VIA are present as elements, binary compounds, ternary compounds, and/or quaternary compound. The elements include Cu, In, and/or Ga, and the multinary metal chalcogenide thin film is denoted by the formula Cu(In)1-x(Ga)x(S)y(Se)1-y)2. A binary compound provides at least some of the at least one element, the binary compound is selected from (Cu)zSe, (Cu)zS, (Cu)zO, (In)zSe, (In)zS, (In)zO, (Ga)zSe, (Ga)zS, and/or (Ga)zO. The binary compound provides at least some of the elements, and is selected from: (In)tSe, (In)tS, (In)tO, (Ga)tSe, (Ga)tS, and/or (Ga)tO. A ternary compound provides at least some of elements, and the ternary compound is selected from CuInS2, CuGaS2, and/or CuInSe2. A quaternary compound provides at least some of the elements. The metal chalcogenide particles comprise a binary chalcogenide denoted by the formula Mm-(VIA)p, the binary chalcogenide comprises at least one element from Group VIA of the Periodic Table. The binary chalcogenide is FeS2, NiS, Bi2S3, PbS, CdS, or Cu2S. The metal chalcogenide particles are deposited on the substrate as nanocrystals synthesized by solution phase chemistry. The nanocrystals are deposited on the substrate by a solution-based technique selected from drop casting, spray coating, inkjet printing, roll coating, knife coating, spin coating, dip coating, and/or web coating. The liquid chalcogen medium comprises an elemental chalcogen, a chalcogen complex, a non-metal chalcogen compound, a metal chalcogen compound, a metal chalcogen salt, and/or a metal (preferably a metal, a metal chalcogen compound, and/or a metal chalcogen salt, especially a metal salt comprising chloride, iodide, oxide, selenide, sulfide, nitrate, sulfate, acetate, acetylacetonate, and/or its dimethyl salt). The precursor film is contacted with the liquid chalcogen medium at 150-350 degrees C, for a period of 30-120 minutes. The metal chalcogenide particles and the liquid chalcogen medium are formulated so that chalcogen in the liquid chalcogen medium is incorporated into the precursor film, resulting in a multinary chalcogenide thin film containing chalcogen from the liquid chalcogen medium. The metal chalcogenide particles and the liquid chalcogen medium are formulated so that chalcogen in the precursor film is exchanged with chalcogen in the liquid chalcogen medium. The precursor film comprises a multinary metal chalcogenide and contact with chalcogen in the liquid chalcogen medium results in sintering of a nanocrystalline or polycrystalline precursor film into larger polycrystalline grain sizes. The method (M3) further involves an annealing step to improve the crystallinity and adhesion of the precursor film. At least one of the solvents comprises a hydrocarbon having 5-20 carbons and at least one functional group selected from amines, carboxylic acids, thiols, phosphines, phosphine-oxides, alkanes, and/or alkenes.x1 and x2=0-1 (preferably 0);y1 and y2=0-1 (preferably greater than 0 and less than 1);x3 and y3=0-1;z=1-2;t=0.5-1;M=metal element (preferably Fe, Ni, Bi, Pb, Cd, Ag, Cu, Zn, W, In, and Bi);m=greater than 0 to less than or equal to 2;p=greater than 0 to less than or equal to 2. EXAMPLE - No suitable example is given.