We report a simple one-step process to enhance power conversion efficiency in poly(3-hexylthiophene)(P3HT):methanofullerene(PCBM) bulk-heterojunction photovoltaic system. The active layer/cathode interface in the organic photovoltaic devices was modified by the commercially available AAO membrane filters. One-step process was achieved by putting the AAO membrane filter on the spin-coated active layer at the wetting condition. The power conversion efficiency of the organic photovoltaics was mainly improved by the absorption in visible light. Diffuse reflectance spectra were obtained by using a UV-Vis-NIR Spectrophotometer. The scanning electron microscopes (SEM), atomic force microscope (AFM), were used to observe surface morphologies of AAO mold and active layers, respectively.