The invention provides a device for obtaining an improved efficiency in a photovoltaic, nanostructured, dye sensitized cell structure, comprising a photoactive working electrode, a counter electrode and an electrolyte arranged there-between. The cell structure thereby forms a tandem cell in that the counter-electrode also is a photoactive electrode, whereby the photoactive working electrode and/or the photoactive electrode are built on a transparent substrate. Furthermore, both the photoactive working electrode and the photoactive electrode are made of porous nanostructured film and the photoactive working electrode is dye sensitized with a first dye. The first dye is selected such that the electron injection into the working electrode is so fast that the red-form of a redox-couple in the electrolyte as fast as possible replaces an injected electron. The second dye is selected such that it has a long lived excited state. In this case the material in the counter electrode is comprised of a semiconductor having a large band gap. In an alternative embodiment, the working electrode is dye sensitized corresponding to the first embodiment, whereas the counter electrode is comprised of a semiconductor with a band gap having absorption in the visible and/or IR region, whereby the light absorption in this electrode is further enhanced by a dye having been adsorbed onto the surface of the electrode.