TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The method comprises, before conducting the synthesis process, preheating the container to 100 degrees C and introducing an inert gas for dewatering and deoxidizing, and where the inert gas is nitrogen, helium or argon. The cooling down step comprises cooling down the multi-element metal chalcogenide to 80 degrees C or lower, and the precipitation step comprises adding a first non-solvent for separating the multi-element metal chalcogenide out, where the first non-solvent is either methanol or toluene, and/or the flushing step comprises flushing the multi-element metal chalcogenide with a second non-solvent, where the second non-solvent is either methanol or toluene, and/or the drying step comprises drying the multi-element metal chalcogenide in a vacuum environment at 50 degrees C for 1 hour. The nanoscale multi-element metal chalcogenide powder is applied in a sputtering process or an ink-printing process for forming a multi-element metal chalcogenide thin film. Preferred Components: The pure metal element powders are simple substances of copper (Cu), indium (In), gallium (Ga), and the chalcogen is simple substances of sulfur (S), selenium (Se) or tellurium (Te). The alloy powders are Cu/In alloy, and Cu/Ga alloy. The multi-element metal chalcogenide has a structure of formula (Cux(In1-yGay)Sez).x = 0.8-1.2;y = 0-1; andz = 1.6-2.4.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The organic solvent is an aromatic amine of formula (a)-(e). (a) is diphenylamine, N-phenylbenzylamine, 2-anilinoethanol or N-phenylethylene-diamine. (b) is 4-butylaniline, 2-biphenylylamine, 2-aminobenzonitrile, N,N-diethyl-1,4-phenylenediamine or o-phenetidine. (c)-(e) is (1,2-phenylenediamine), (1,3-phenylenediamine), (1,4-phenylenediamine) or (4-methyl-1,3-phenylenediamine). The organic solvent is a mixture of two different solvents.R1, R2 = H, aryl, 1-5C amine or 1-5C alcohol group;R = H, 1-10C alkyl, 1-10C amine, 1-10C alkoxy, nitrile or aryl; andR3 = H, 1-10C alkyl, nitrile or aryl. EXAMPLE - A 500 ml container, e.g. a three-necked bottle, was heated to 100 degrees C, and then an inert gas (e.g. nitrogen) was introduced into the container to dewater and deoxidize for 1 hour. Gallium ingot (0.04 mole) heated to 30 degrees C, copper powder (0.18 mole), indium powder (0.16 mole), and selenium powder (0.44 mole), were provided with nitrogen and maintained under a temperature of 200 degrees C for 0.5 hours. Then the gallium ingot, copper (Co) powder, indium powder (In), and selenium (Se) powder were put in the container, in which the mole ratio of the ingredients of the mixture (Co:In:Ga:Se) was 0.18:0.16:0.04:0.38. Then 2-aminobenzonitrile (1.2 mole) was added into the container for dissolving the gallium ingot, the copper powder, the indium powder and the selenium powder. The 2-aminobenzonitrile had a boiling point higher than 240 degrees C, and had a pH of 7-10. A magnet was employed to stir the mixture for 1 hour, and the mixture was slowly heated to 240 degrees C. After the temperature of the mixture was stably maintained at 240 degrees C, the operation condition was maintained for 24 hours. The operation temperature was cooled down to 80 degrees C or lower, and then 160 ml of dewatered methanol was introduced to deposit, filter, and separate out black copper-indium-gallium-selenide (CIGS) sediment powder. The CIGS sediment powder was flushed with methanol. The CIGS powder was dried in a vacuum environment at a temperature of 50 degrees C or above for 1 hour.