We demonstrate enhanced power conversion efficiency in organic photovoltaic (OPV) cells incorporated into a plasmonic nanocavity array. The nanocavity array is formed between a patterned Ag anode and an unpatterned Al cathode. This structure leads to the confinement of optical energy and enhanced absorption in the OPV. Devices characterized under simulated solar illumination show a 3.2-fold increase in power conversion efficiency compared to OPVs with unpatterned Ag anodes. The observed enhancement is also reflected in the external quantum efficiency, and the spectral response is consistent with optical finite-difference time-domain simulations of the structure.