We have fabricated efficient heterojunction organic photovoltaic (OPV) cells based on pentacene-doped copper(II) phthalocyanine (CuPc) layer as donor and fullerene (C60) layer as acceptor. The power conversion efficiency of 4% pentacene-doped CuPc/C60 OPV cell (3.06%) is increased by 77% compared with that of the standard CuPc/C60 OPV cell (1.73%). The efficiency improvement can be attributed to the higher carrier mobility instead of the stronger photon absorption of the pentacene-doped CuPc layer.