TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The chalcogenide semiconductor material is selected from IV-VI, I-III-VI and I-II-IV-VI compounds. The sodium source includes at least one of sodium ions, sodium-containing compound particles or sodium-containing micelles. A mole fraction of the sodium ions in the ink composition is at 0.01-10.0 (preferably 0.25-0.5) mole%. The nanoparticles include at least two different metal chalcogenide. The metals of the nanoparticles, metal ions and metal complex ions include tin, copper and zinc, and further include germanium; or include copper, indium and gallium. The nanoparticles includes at least one of Sn-S, Cu-S, Zn-S, In-S, Ga-S, Sn-Se, Cu-Se , Zn-Se, In-Se, Ga-Se, CuSn-S, Cu-Zn-S, Zn-Sn-S, Cu-In-S, Cu-In-Ga-S, Cu-Sn-Se, Cu-Zn-Se, Zn-Sn-Se, Cu-In-Se, Cu-Ga-S, Cu-Ga-Se, Cu-In-Ga-Se, Cu-S-Na, Sn-S-Na, Zn-S-Na, In-S-Na, Ga-S-Na, Cu-In-S-Na, Cu-Ga-S-Na, In-Ga-S-Na, Cu-Zn-S-Na, Cu-Sn-S-Na, Zn-Sn-S-Na, Cu-In-Ga-S-Na, Cu-Zn-Sn-S-Na, Cu-Se-Na, Sn-Se-Na, Zn-Se-Na, In-Se-Na, Ga-Se-Na, Cu-In-Se-Na, Cu-Ga-Se-Na, Cu-Zn-Se-Na, Cu-Sn-Se-Na, Zn-Sn-Se-Na, In-Ga-Se-Na, Cu-In-Ga-Se-Na, and Cu-Zn-Sn-Se-Na. The metal complex ions include at least one of metal-thiourea ions, metal-selenourea ions, metal-thioacetamide ions and metal-ammonium sulfide ions. The sodium salt includes sodium hydroxide, sodium oxide, sodium amide, sodium halide, sodium chalcogenide, carboxylic sodium, sodium sulfonate or a sodium salt of polyacrylic acid.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: At least 95% of the solvent system is water. The solvent system includes polar solvents; and at least one solvent selected from water, methanol, ethanol and isopropyl alcohol, dimethyl sulfoxide (DMSO) and amines. Preferred Method: The step of incorporating the sodium into the solvent system includes at least one of adding sodium ions, sodium-containing particles and sodium containing micelles. The step of adding sodium ions includes dissolving a sodium salt. EXAMPLE - Metal chalcogenide nanoparticles were prepared as follows: Tin chloride (5 mmol) was dissolved in H2O (25 ml) to form an aqueous solution (A1). Thioacetamide (4 mmol) was dissolved in H2O (40 ml) to form an aqueous solution (B1). The aqueous solutions (A1) and (B1) were mixed to form a reaction solution (C1). The reaction solution (C1) was added with 30% NH4OH (12 ml) and stirred under 65 degrees C for 1.5 hour. The resulting brown-black precipitates were collected to provide tin sulfide (Sn-S) nanoparticles. Metal complex ions were prepared as follows: copper nitrate (7 mmol) was dissolved in H2O (5 ml) to form an aqueous solution (D1). Thioacetamide (10 mmol) was dissolved in H2O (5 ml) to form an aqueous solution (E1). The aqueous solutions (D1) and (E1) were mixed to form a reaction solution (F1). The reaction solution (F1) was stirred under room temperature for 0.5 hours to form copper-thioacetamide ions. The collected tin sulfide (Sn-S) nanoparticles were mixed with the reaction solution (F1) to form a mixture solution (G1). Metal ions were prepared as follows: zinc nitrate (4.8 mmol) was dissolved in H2O (5 ml) to form an aqueous solution (H1) containing zinc ions. The aqueous solution (H1) was mixed with the mixture solution (G1) and stirred overnight to form an ink. The obtained ink is a well-mixture of copper, zinc, tin and sulfur and thus used to form a Cu2ZnSnS4 (CZTS) film.