Efficiency of organic solar cells shows a strong improvement when the transparent conductive anode (indium tin oxide-ITO, aluminium-doped zinc oxide-AZO, fluorine-doped tin oxide-FTO), is covered with an ultra-thin metallic film. It is shown that the best results are achieved with a gold film (0.5 nm). The efficiency of the solar cells using AZO or FTO is improved up to one order of magnitude, while in the case of ITO it is at least 50%. It is shown that if the matching between the work function of the anode and the highest occupied molecular orbital (HOMO) of the organic electron donor is the most important factor limiting the hole transfer efficiency, others factors such as transparent conductive oxide (TCO) surface roughness and adhesion of the organic layer are also key factors. (c) 2008 Elsevier B.V. All rights reserved.