TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The preparation of nanoparticles is performed using any one selected from a low-temperature colloidal process, solvent heat synthesis process, microwave process and an ultrasonic synthesis process. Preparing the slurry involves subjecting the nanoparticles to mixing with a binder, dissolving in a solvent and treating with ultrasound to disperse them. Applying the slurry on the substrate is performed using any one selected from spraying, ultrasonic spraying, spin coating, doctor blading, screen printing or ink-jet printing. The method further involves performing drying in two stages. The thermal treatment is performed at 400-530 degrees C for 10-60 minutes.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The solvent is alcoholic solvent selected from ethanol, methanol, pentanol, propanol and butanol. The binder includes at least one selected from ethyleneglycol, propyleneglycol, ethylcellulose, polyvinylpyrrolidone, ethylenediamine, monoethanolamine, diethanolamine or triethanolamine. EXAMPLE - In a glove box, copper(I)iodide (0.343 g) and indium(III)iodide (0.991 g) were mixed with distilled pyridine solvent (30 ml), and the resultant mixture was stirred for 10 minutes on a hot plate at 50 degrees C. After stirring for 10 minutes, the opaque solution was made transparent. The copper/indium (Cu/In) mixture was mixed with Sodium sulfide (Na2S) (0.312 g) in distilled methanol (20 ml), so as to correspond to the atomic ratio of Cu:In:Se = 0.9:1:2. Then, the mixture of methanol and pyridine was mechanically stirred in an ice bath at 0 degrees C and reacted for 1 minutes, thus synthesizing CIS nanoparticles. The synthesized CIS colloid was centrifuged at 4000 rotation per millions (rpm) for 30 minutes, treated with ultrasound for 5 minutes, and washed with distilled methanol, and these procedures were repeated to completely remove by-products and pyridine from the product, resulting in high-purity CIS compound nanoparticles. Then, the CIS precursor nanoparticles (0.3 g), propylene glycol binder (0.3 g), monoethanolamine (0.5 g), and methanol solvent (1.2 g) were mixed, and treated with ultrasound for 30 minutes to disperse them, thus preparing slurry. The slurry thus prepared was applied using spin coating on a soda-lime glass substrate having deposited molybdenum (Mo). The spin coating was carried out at 1000 rpm for 20 seconds. After completion of the application of the slurry on the Mo/glass substrate, two-stage drying was performed to remove the alcoholic solvent and the binder. The coated glass substrate was primarily dried on a hot plate at 100 degrees C for 3 minutes, and then secondarily dried at 300 degrees C for 5 minutes. The coating and drying procedures were repeated five times thus forming a CIS compound thin film on the glass substrate. Finally, selenization was performed to replace sulfur of the CIS precursor thin film with selenium. Specifically, while gaseous Se was supplied at a substrate temperature of 500 degrees C, thermal treatment was performed for 30 minutes, thus obtaining dense Cu-In-Se compound thin film.