Enhancement in the efficiency of air processed bulk heterojunction photovoltaic devices is demonstrated via the addition of highly stable uncapped gold (Au) and aluminum (Al) nanoparticles (NPs) into the photoactive layer. An enhancement in conversion efficiency by 15% is observed, which can be attributed to Localised Surface Plasmon Resonance effects at the small diameter Au NPs and to efficient scattering by the large diameter Al NPs.