We evaluate an ordered organic-inorganic solar cell architecture based on CdS QD-decorated ZnO nanorod arrays encased in the hole-conducting polymer Poly(3-hexylthiophene-2,5-diyl)(P3HT). In this work, CdS quantum dot with different sizes were attached to the surface of the nanorods capped with mercaptopropionic acid. The results show that the CdS QDs on the ZnO nanorods increase both the open circuit voltage(VOC)and short circuit current density(JSC)relative to devices without CdS QDs. A photovoltaic device based that has been decorated with CdS QDs yields power conversion efficiency over 4 times greater than that for a similar device without CdS QDs. The best device yields a short circuit current density of 1.38 mAcm-2 under AM1.5 illumination(100 mW cm-2), resulting in a power conversion efficiency of 0.21% The increase shows that the modification with CdS QDs can serve not only as a photosensitizer but mainly as an energy funnel and/or an electronic mediator to significantly improve the electron injection efficiency from P3HT to ZnO nanorods.