A method of manufacturing a solar cell having increased light efficiency due to increased gallium distribution on a surface of a light absorption layer, the method including forming a first electrode on a substrate, forming a precursor that includes at least one of copper, gallium, and indium on the first electrode, forming a preliminary light absorption layer by providing selenium to the precursor, forming the preliminary light absorption layer further including performing a heat treatment, and forming a liquid state CuSe compound, forming a light absorption layer by providing a compound including at least one of gallium and indium to the preliminary light absorption layer, and forming a second electrode on the light absorption layer.