Transient photovoltage and differential charging experiments have been carried out to investigate the plasmonic effects in organic photovoltaic devices (OPVs). We observed that the carrier lifetimes became longer after the Au nanoparticles were blended into the OPVs. Additionally, the charge carrier densities also became higher in the bulk of the device. The carrier lifetime, however, usually follows an inverse power relationship with the increasing charge density in OPVs fabricated base on the concept of bulk heterojunctions. Therefore, we conclude that one of the limitations for the plasmonic approaches could be the strong bimolecular recombination.