NOVELTY - A copper-indium-gallium selenide thin film solar cell comprises substrate having back electrode layer, light-absorption layer, transition layer, intrinsic layer and transparent conductive film layer. The back electrode layer is molybdenum layer or molybdenum-copper alloy layer. The light absorption layer has gradient energy band distribution structure. The transition layer is zinc sulfide film. The transparent conductive film layer is aluminum-doped zinc oxide (ZAO) film.    USE - Copper-indium-gallium selenide thin film solar cell.    ADVANTAGE - The copper-indium-gallium selenide thin film solar cell has improved photoelectric conversion efficiency and gradient energy band, and is manufactured by environmentally-friendly process with improved controllability, and without using cadmium and hydrogen selenide.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for preparation of copper-indium-gallium selenide (CIGS) thin film solar cell, which involves ultrasonically cleaning glass substrate using solvent for 5-30 minutes, drying at 50-150 degrees C in an oven, providing obtained substrate into vacuum chamber, introducing process gas, and sputtering molybdenum target or co-sputtering molybdenum and copper target to obtain molybdenum layer or molybdenum-copper alloy layer as back electrode layer, providing back electrode layer of the glass substrate into vacuum chamber with copper-indium-gallium selenide (CuInxGa(1-x)Se) target, and sputtering to obtain CIGS light absorption layer, sputtering the light absorption layer with gallium-copper target or aluminum target at 100-500 degrees C to form gradient in the light absorption layer, heating continuously, annealing at 150-550 degrees C for 10-60 minutes, cooling to room temperature, carrying out magnetron sputtering of zinc sulfide target to obtain zinc sulfide transition layer, and preparing intrinsic zinc oxide and transparent conductive film layer by magnetron sputtering of zinc oxide target and aluminum-doped zinc oxide target.