Solution-processed ultrafine gold nanowires (Au-NWs) have been exploited as plasmonic antennae in organic P3HT:PCBM photovoltaic cells. The careful reduction of the spacer layer thickness which allows the evanescent field to be extended into the photoactive layer and the geometry of the Au-NWs bands which favors the enhanced scattering collectively result in an increased short-circuit current density by 23.2%. The exact nature of the plasmonic effect in Au-NWs incorporated P3HT system and the critical role played by the spacer layer were studied through optical and time-resolved photoluminescence spectroscopy. The improved photocurrent in the Au-NWs integrated devices is due to an enhanced absorption in the photoactive layer which is contributed from an increased plasmon excitation field and far-field scattering of Au-NWs.