A micro-prism array (MPA) integrated with subwavelength structures (SWSs) was employed to improve the efficiency of a CuIn1-xGaxSe2 (CIGS) solar cell by minimizing optical reflection losses caused by the metal grids. The MPA mounted on the CIGS solar cell refracted incident light normal to the grid into the nearby surface of the solar cell, thereby minimizing the optical reflection losses caused by the metal grids. Furthermore, to reduce reflection losses at the surface of the MPA, SWSs were formed on the MPA glass. This resulted in increased photovoltaic current, which enhanced the power conversion efficiency (PCE) of the solar cells. The final short circuit current density and the PCE of the CIGS solar cells with MPA glass integrated with SWSs were improved by 9.0% and 8.5%, respectively, compared with those of a CIGS solar cell without cover glass.