Provided are a CIGS solar cell and a method of fabricating the CIGS solar cell. In the method, a buffer layer exposing protrusions is formed. Then, a window electrode layer having an uneven surface conforming with the protrusions of the buffer layer is formed. Thus, an additional process for making the upper surface of a window electrode layer rough is unnecessary in order to decrease surface reflectance of incident sunlight and increase the solar cell efficiency, so that productivity can be improved.