TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The viscosity of the first paste is different by 400-1500 cP from that of the second paste. The first paste and the second paste have viscosities of 700-1500 cP and 50-300 cp respectively. The method (II) further comprises forming a third paste layer on the second paste layer, where the ratios of the concentration of the copper element to the sum of the concentrations of the indium and gallium elements in the first, second and third paste layers are 1:0.9-1.3:0.9-1.3, and the concentration distributions of the gallium element in the paste layers are adjusted such that the ratios of the concentration of the gallium element to that of the copper element in the first and third paste layers are greater by 0.1-0.9 than the ratio of the concentration of the gallium element to that of the copper element in the second paste layer. The steps (e) and (f) are carried out at 250-550degree C and 400-600degree C, respectively, the sulfur gas atmosphere is a hydrogen sulfide gas or sulfur vapor atmosphere, and the selenium gas atmosphere is a hydrogen selenide gas or selenium vapor atmosphere. The step (c) further comprises drying the first paste coated on the conductive substrate in an air atmosphere at 100-300degree C. The step (d) further comprises drying the second paste coated on the first paste layer in an air atmosphere at 100-300degree C. Preferred Components: The first organic binder is ethyl cellulose or a mixture comprising 90-99.9 pts. wt. of ethyl cellulose and 0.1-10 pts. wt. of polyvinyl acetate, palmitic acid, polyethylene glycol, polypropylene glycol, polypropylene carbonate and/or propylenediol. The second organic binder is polyvinyl acetate or a mixture comprising 90-99.9 pts. wt. of polyvinyl acetate and 0.1-10 pts. wt. of ethyl cellulose, palmitic acid, polyethylene glycol, polypropylene glycol, polypropylene carbonate and/or propylenediol. The ratios of the concentration of the copper element to the sum of the concentrations of the In element and gallium element in the first paste layer and the second paste layer are 1:0.9-1.1, and the ratio of the concentration of the gallium element to that of the copper element in the first paste layer is different by 0.1-0.9 from the ratio of the concentration of the gallium element to that of the copper element in the second paste layer. The copper precursor is a hydroxide, nitrate, sulfate, acetate, chloride, acetylacetonate, formate or oxide of copper and/or a hydroxide, nitrate, sulfate, acetate, chloride, acetylacetonate, formate or oxide of a copper/indium or copper/gallium alloy. The indium precursor is a hydroxide, nitrate, sulfate, acetate, chloride, acetylacetonate, formate or oxide of indium and/or a hydroxide, nitrate, sulfate, acetate, chloride, acetylacetonate, formate or oxide of an indium/copper or indium/gallium alloy. The gallium precursor is a hydroxide, nitrate, sulfate, acetate, chloride, acetylacetonate, formate or oxide of gallium, and/or a hydroxide, nitrate, sulfate, acetate, chloride, acetylacetonate, formate or oxide of a gallium/copper or gallium/indium alloy. The first and second paste further comprises a dispersant comprising a -terpineol, ethylene glycol, thioacetamide and/or ethylenediamine. The first and second pastes each independently further comprise a dopant comprising sodium, potassium, nickel, phosphate, arsenic, antimony and/or bismuth and the dopant is present at 1-100 pts. wt. based on 100 pts. wt. of the first metal precursor(s) and the second metal precursor(s). EXAMPLE - 1 g Copper nitrate, 0.4 g gallium nitrate and 1.12 g indium nitrate were dissolved in 80 ml ethanol. The solution was mixed with 20 ml solution of 13.7 g terpineol and 0.75 g ethyl cellulose in ethanol with stirring. The ethanol was removed by evaporation at 40degree C for 1 hour to obtain a copper indium gallium precursor paste having a sufficiently high viscosity. The paste was spin coated on a molybdenum glass substrate and dried on a hot plate at 150degree C for 3 minutes. After drying, the substrate was thermally treated in a furnace in an air atmosphere at 350degree C for 1 hour and in a sulfur vapor atmosphere at 500degree C for 30 minutes to obtain a copper indium gallium selenide thin film.