TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Materials: The Group 1B metal selenide is a copper selenide (Cu-Se). The Group 3A metal selenide is an indium selenide (In-Se) or gallium selenide (Ga-Se). The paste further includes sodium (Na), potassium (K), nickel (Ni), phosphorus (P), arsenic (As), antimony (Sb), or bismuth (Bi) as dopant. The compound of the absorption layer is copper indium gallium selenide (Cu(In,Ga)Se2).Preferred Process: The Cu-Se is prepared by prepared by adding a copper salt and selenious acid (H2SeO3) to a solvent and heating the mixture. The In-Se is prepared by adding an indium salt and H2SeO3 to a solvent and heating the mixture. The rapid thermal processing is carried out at 400-600degreesC for 1-30 minutes.Preferred Properties: The metal selenide particles have a particle diameter of 5 nm to 10 microns (preferably 50 nm to 5 microns).Preferred Composition: The mole ratio of copper (Cu) to the total of indium and gallium (In+Ga) is 0.6-1.5 and the mole ratio of gallium (Ga) to the total of gallium and indium (Ga+In) is 0-0.5, when Cu-Se is used as the Group 1B metal selenide and In-Se and/or Ga-Se are used as the Group 3A metal selenide. The coating layer has a monolayer or multilayer structure and a total thickness of 3-5 microns, preferably a trilayer structure where the bottom first layer has a mole ratio of Cu/(In+Ga) of 0-0.9 and a thickness of 0.1-1.0 microns, the intermediate second layer has a mole ratio of Cu/(In+Ga) of 0.8-3.0 and a thickness of 0.5-3.0 microns and the top third layer has a mole ratio of Cu/(In+Ga) of 0-0.9 and a thickness of 0.1-1.0 microns.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Compounds: The solvent of the paste is water, alcohol-based compound, carbonate-based compound or glycol-based compound. EXAMPLE - A 0.03 M copper nitrate and a 0.02 M selenious acid were mixed in ethylene glycol (250 mL). The resulting reaction solution was heated to 170degreesC and reacted for 3 hours to prepare copper selenide (CuSe) nanoparticles. A 0.02 M indium nitrate and a 0.02 M selenious acid were mixed in diethylene glycol (250 mL). The resulting reaction solution was heated to 170degreesC and reacted for 3 hours to prepare indium selenide (InSe) nanoparticles. The CuSe and InSe nanoparticle powder was dispersed in alpha-terpineol and propylene carbonate as solvents and polypropylene carbonate as binder to prepare a paste. The weight ratio among terpineol/propylene carbonate/polypropylene carbonate/powder was 43.34:26.65:5.01:25. The resulting paste was coated on a glass substrate, followed by rapid thermal annealing at 430degreesC for 2 minutes under nitrogen atmosphere to prepare copper indium selenide (CuInSe2).