NOVELTY - The method comprises: forming a nano pattern on a side of a substrate using a nano imprinting mode for enhancing an absorption efficiency of an incident light; forming a transparent electrode in a portion of the substrate; forming a photoactive layer on the transparent electrode to absorb light and to create electrons and holes; and forming a reflective electrode on the photoactive layer. The nano pattern formation step comprises forming a resin nanoimprint on the side of the substrate, transferring the pattern into a nanoimprint mold, pressurizing the mold, and dry etching the pattern.    USE - The method is useful for fabricating a solar cell (claimed).    ADVANTAGE - The nano pattern is formed on the surface of the substrate and the incident light is diffused to the substrate, so that the light loss of the cell can be reduced, thus improving the optical absorption efficiency and an element efficiency of the cell. The imprint mold can be repetitively reused. The solar cell is fabricated in a cost-effective manner with low processing time.    DETAILED DESCRIPTION - The method comprises: forming a nano pattern on a side of a substrate using a nano imprinting mode for enhancing an absorption efficiency of an incident light; forming a transparent electrode in a portion of the substrate; forming a photoactive layer on the transparent electrode to absorb light and to create electrons and holes; and forming a reflective electrode on the photoactive layer. The nano pattern formation step comprises forming a resin nanoimprint on the side of the substrate, transferring the pattern formed into a nanoimprint mold, pressurizing the nanoimprint mold, separating the resin nanoimprint from the nanoimprint mold, and dry etching the pattern. The method further comprises removing the nanoimprint resin, and performing the dry etching until the nanoimprint resin is removed from the side of the substrate, where the pattern of the nanoimprint mold is formed using the anodized aluminum oxide method, a photo chemical etching method or an electron-beam lithography method.