We demonstrate enhanced performance of a hybrid photovoltaic device, where poly[3-hexylthiophene] (P3HT) is used as active material and a solution-processed thin flat film of ZnO modified by a self-assembled monolayer (SAM) of phenyl-C61-butyric acid (PCBA) is used as electron extracting electrode. Ultraviolet photoemission spectroscopy measurements reveal an increase in the substrate work function from 3.6 to 4.1 eV upon PCBA SAM deposition due to an interfacial dipole pointing away from the ZnO. External quantum efficiency (EQE) of the SAM modified devices reached 9%, greatly improved over the 3% EQE of the unmodified devices. This corresponds to full charge separation of all photoexcitations generated in the P3HT within an exciton diffusion range from the interface.