NOVELTY - The copper-selenide-diamine coordination compound (1) is dissolved in a liquid solvent, to obtain liquid copper-selenide-diamine solution. The copper-selenide-diamine solution is deposited on a substrate and heated. The solvent is vaporized and the copper-selenide-diamine coordination compound is decomposed, to form crystalline copper-selenide film on the substrate. Thus, formation of crystalline copper-selenide film is carried out.    USE - Formation of crystalline copper-selenide film used for thin-film semiconductor and absorber layers of solar cell. Uses of the crystalline copper-selenide film include but are not limited to thin film tandem cells and channel layers of transistors.    ADVANTAGE - The method economically provides crystalline copper-selenide film with high quality, large area, durability and without using vacuum deposition techniques.    DETAILED DESCRIPTION - The copper-selenide-diamine coordination compound (1) is dissolved in a liquid solvent, to obtain liquid copper-selenide-diamine solution. The copper-selenide-diamine solution is deposited on a substrate and heated. The solvent is vaporized and the copper-selenide-diamine coordination compound is decomposed, to form crystalline copper-selenide film on the substrate. Thus, formation of crystalline copper-selenide film is carried out. The copper-selenide-diamine coordination compound is of formula: Cu2Sex, where x is 1-12. The copper-selenide-diamine coordination compound is formed by reaction of copper-selenide and selenium in presence of ethylene diamine, 1,3-diaminopropane or 1,2-diaminobenzene. The copper-selenide-diamine coordination compound is dissolved in dimethylsulfoxide (DMSO) or ethylene diamine. The volatile products such as selenium and/or hydrogen-selenide are vaporized. A copper-indium-diselenide film and/or copper-indium-gallium-diselenide film are formed using a soluble copper-selenium precursor and a di-functional diamine. An indium-selenide film is formed using indium selenide compound of formula: In2Se4(enH)x(N2H5)2-x(en)y(N2H4)z, where x is 0-2, y is greater than or equal to 1 and z is greater than or equal to 0. The indium selenide compound is dissolved in a mixture of dimethylsulfoxide and ethanol amine or mixture of hydrazine and ethylene diamine. The copper-selenide film is formed using a copper-organoselenide precursor. The organoselenide precursor is copper alkyl selenide, copper aryl selenide or copper-n-butyl selenide. The copper-n-butyl selenide is formed by reacting n-butyl selenide and a copper salt. The copper salt is copper coordination complex such as tetracyanomehtylcopperhexafluorophosphate complex of formula: (Cu(CH3CN)4)(PF6), copper halide such as copper iodide, copper bromide, copper chloride or copper methoxide. The n-butyl selenide is formed using n-butyl lithium and selenium. The copper organoselenide is formed by reacting an organoselenide and copper salt or by reacting an organometallic reagent with selenium. The organometallic reagent is organolithium reagent, alkyllithium reagent such as n-butyl lithium, t-butyl lithium, secondary-butyl lithium, methyl lithium, phenyl lithium, tolyl lithium, xylyl lithium or 2,6-diisopropylphenyl lithium. The indium-selenide film is formed using indium-selenide (In2Se3) nanoparticles. The indium-selenide nanoparticles are formed by reaction of indium iodide and sodium selenide in presence of methanol. The indium-selenide film is formed using indium-selenide, selenium, hydrazine and ethylene diamine. An INDEPENDENT CLAIM is included for formation of copper-indium-diselenide film, copper-indium-gallium-diselenide film and indium-selenide film.