A lithography free approach to fabricating optically thin (∼10 nm) noble metal electrodes with a dense array of sub-wavelength apertures is reported. These nano-structured electrodes support surface plasmon resonances which couple strongly with visible light concentrating it near to the electrode surface. They are also remarkably robust and can be fabricated on glass and plastic substrates with a sheet resistance of <15 Ω sq−1. As the window electrode in solution processed and vacuum deposited organic photovoltaics (OPV) the photocurrent is increased by as much as 28% as compared to identical devices without apertures, demonstrating that the apertures do not need to have a tight size and/or shape distribution to be effective. As a drop-in replacement for the indium-tin oxide electrode in flexible OPV these plasmon-active electrodes offer superior performance; 5.1% vs. 4.6%, demonstrating that this class of electrode is a truly viable alternative to conducting oxide window electrodes for OPV.