TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The method further involves washing the crude cake with a washing solution containing water, alcohol and ketone before the post-treatment; filtering the treatment mixture after the post-treatment to obtain a treated crude cake, followed by washing the treated crude cake with a washing solution containing water, alcohol and ketone; and washing the treated crude cake with an acid. Preferred Components: Each of the first and second solvents is selected from alkylamine, dimethyl foramide, N-methylpyrolidone, methylimidazole, dimethyl sulfoxide, oleyamine, glycerol, and ethyleneglycol. Each of the first and second solvents is selected from ethylenediamine and methylimidazole. The reaction mixture includes at least one first compound and at least one second compound, the first compound containing M1 and A1, the second compound containing M2 and A1. The reaction mixture includes Cu2Se and In2Se3; Cu2Se, In2Se3 and Ga2Se3; Cu2Se, In2S3, and Ga2Se3; Se, InCl3.4H2O, and CuCl; InCl3, Na2Se, and CuCl; or InCl3, GaCl3, Na2Se, and CuCl.A1=S, Se, Te, Cl-, Br-, I-, OH-, NO3-, SO42-, CH3COO-, acetylacetonate, and combinations of S, Se, and Te.When A1 of the first and second compounds is Cl31, Br-, I-, OH-, NO3-, SO42-, CH3COO31, acetylacetonate, the reaction mixture further includes a powder of material selected from S, Se and/or Te. EXAMPLE - Ethylenediamine (9000 ml) was added into a reactor. In2Se3 (600 g) and Cu2Se (260 g) were added into the reactor with stirring. The mixture in the reactor was stirred for 5 minutes before heating and was heated to a boiling point with stirring for reaction of the mixture to take place. The reaction of the mixture lasted under reflux condition for 30 hours. The mixture was filtered to obtain a crude cake of CuInSe2 after the reaction was completed and the mixture was cooled. The crude cake was washed with a solution containing a large amount of water, ethanol (2 l) and acetone (2 l), followed by drying at 150 degrees C. A black powder of CuInSe2 (a1) having a composition of Cu (25.43 at.%), In (26.68 at.%) and Se (47.89 at.%) was obtained. Ethylenediamine (6000 ml) was added into a reactor. Black powder of CuInSe2 (a1) (730 g) and Se powder (44 g) were added into the reactor with stirring. The mixture in the reactor was stirred for 5 minutes before heating and was subsequently heated to its boiling point with stirring for 40 hours for conducting a post treatment of black powder of CuInSe2 of the mixture under reflux condition. The mixture was filtered to obtain a crude cake of CuInSe2. After the post treatment was completed and the mixture was cooled. The crude cake was washed with a solution containing a large amount of water, ethanol (2 l) and acetone (2 l), followed by drying at 150 degrees C. A black powder of CuInSe2 (b1) having a composition of Cu (25.44 at.%), In (26.67 at.%), and Se (47.88 at.%) was obtained. The post treatment of product permitted a significant reduction of the carbon content of the CuInSe2 product from 1.536 wt.% to 0.877 wt.%.