TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The precursors of Cu, In and optional Ga are mixed in a mole ratio of 1:0.5:0 to 1:2:2. In step (B), the oxide mixture is mixed with the Se precursor in a mole ratio of 1:0.5 to 1:2. The heat treatment in step (A) is conducted at 500-900 degrees C. In step (A), the precursors of Cu, In, and optional Ga are mixed by dispersing them in water or alcohol, optionally at a pH of less than 10. In step (B), the resulting mixture including the Se precursor is heated to obtain a CIGS-based powder, followed by adding the powder to an aqueous or alcohol solvent to obtain the paste; where, a dispersing agent and/or a binder is further added in step (B). The sulfur-containing compound is further added in step (A) or (B). The elements selected from sodium (Na), potassium (K), nickel (Ni), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi) are further added as a dopant in step (A) or (B). In step (C), the coating is conducted by a method of doctor blade coating, screen coating, spin coating, spray coating or paint coating; the heat treatment is conducted at 200-700 degrees C (preferably heat treatment is conducted under ambient atmosphere at 100-400 degrees C, and is followed by heat treatment under inert or reducing gas atmosphere (preferably gaseous hydrogen as reducing gas). The thickness of the coating layer obtained in step (C) is 0.5-10 mu m. Preferred Components: The precursor of the copper (Cu), indium (In) or gallium (Ga) is the corresponding hydroxide, nitrate, sulfate, acetate, chloride, or oxide. The Se precursor is selenium tetrachloride (SeCl4), selenium sulfide (SeS2), sodium selenide (Na2Se), sodium selenite (Na2SeO3), and/or sodium selenite pentahydrate (Na2SeO3.5H2O). The sulfur-containing compound is hydrogen sulfide (H2S), or sodium sulfide (Na2S).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The precursor of the copper (Cu), indium (In) or gallium (Ga) is corresponding acetylacetonate, or formate. The dispersing agent is alpha -terpienol, ethylene glycol, and/or thioacetamide. The binder is palmitic acid. The sulfur-containing compound is a thiol of formula RSH, or thioacetamide.R=alkyl, or carboxyalkyl.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The binder is ethyl cellulose, polyethylene glycol, polypropylene glycol, and/or polypropylene carbonate. EXAMPLE - Copper nitrate trihydrate (Cu(NO3)2.3H2O) (7.77 g), indium nitrate trihydrate (In(NO3)2.3H2O) (10.23 g) and gallium nitrate trihydrate (Ga(NO3)2.3H2O) (8.7 g) were dissolved in water (30 ml), the pH was adjusted for 7 using 1M sodium hydroxide and stirred for a day. The precipitates were isolated by filtering, dried at 110 degrees C for a day, and then heated at 800 degrees C for 5 hours to obtain a copper-indium-gallium (CIG) oxide (CuInGaO4). The resulting CIG oxide (0.83 g) and SeCl4 (1.17 g) were added to ethanol (50 ml), and then stirred thoroughly to obtain a copper-indium-gallium-selenide (CIGS) precursor mixture. A dispersing agent such as alpha -terpienol (10 g) and a binder such as ethyl cellulose (0.75 g) were dissolved in ethanol (20 ml), mixed with the CIGS precursor mixture, and the resulting mixture was stirred, followed by evaporating the solvent at 40 degrees C to obtain a CIGS paste. The CIGS paste was coated on a glass plate using a doctor blade method, and the resulting coat was heated at 400 degrees C for 40 minutes under a hydrogen/argon (H2/Ar) (5:95) atmosphere to obtain a CIGS thin film.