TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The flexible substrate is made of transparent polyethylene sulfone, polycarbonate, polyethylene terephthalate, polyimide, or stainless steel. In the copper indium gallium selenide single target, the composition ratio of: copper is 0.7-1; indium is 0-1; gallium is 0-1; and selenide is 2. Preferred Method: The light absorption layer containing copper indium selenide and copper gallium selenide single target are simultaneously evaporated at temperature of 200 degrees C on the flexible substrate and the stable thin film is formed by depositing indium and gallium according to the crystallographic compositional ratio. In the step (ii), the copper indium selenide and copper gallium selenide single target are simultaneously deposited to form copper indium selenide-copper gallium selenide absorber thin film. In the step (ii), depositing copper indium gallium selenide single target to form copper indium gallium selenide absorber thin film. The sputtering process condition is as follows: the sputtering process power is 100 W (1.23W/cm2) to 300 W (3.70W/cm2), the work pressure is 0.1-1 Pa, the time is 0.5-2 hours, and the temperature is room temperature of 200 degrees C. Copper indium gallium selenide absorber thin film is deposited on the flexible substrate, and the X-ray diffraction (XRD) analysis result represents increased substrate temperature, chalcopyrite structure without secondary phase and improved crystallization, the peak intensity is increased and full width at half maximum is decreased according to the Raman PL characteristic; and copper indium gallium selenide target composition ratio meets the band gap as the substrate temperature increases. Copper indium gallium selenide light absorbing layer is deposited simultaneously on copper indium selenide, copper gallium selenide single target flexible substrate, according to XRD analysis result shows increased substrate temperature, chalcopyrite structure without secondary phase and improved crystallization, increasing copper indium selenide or copper gallium selenide Raman PL characteristics area having close characteristic to each Raman shift values, and the indium and gallium composition ratio meets optical band gap constant distribution function.