A method of fabricating a solar cell includes forming a first electrode on a transparent substrate; forming a first impurity-doped semiconductor layer on the first electrode; forming a light absorption layer on the first impurity-doped semiconductor layer and including a plurality of sub-layers, the plurality of sub-layers having stepwisely varying energy band gaps; forming a second impurity-doped semiconductor layer on the light absorption layer; and forming a second electrode on the second impurity-doped semiconductor layer.