sensitized solar cells (DSCs), [ 2 ] are based on low-cost materials and can be fabricated by means of simple printing techniques. Two transparent fl uorine-doped tin oxide (FTO) coated glass substrates are conventionally used as collecting electrodes to extract photogenerated charge carriers from the dye-sensitized junction. These substrates account for a major fraction of the fabrication costs while also compromising the DSC performance due to their limited transmission and conductivity. Here, we demonstrate that back-contact solar cell confi gurations, successfully developed to increase the performance of silicon solar cells, can be used to address these limitations. For the fi rst time, we report the successful fabrication of a monolithic back-contact dye-sensitized solar cell (BC-DSC) based on an array of two interdigitated fi nger electrodes located on one common substrate. In photovoltaic cells, light absorption results in the generation of charge carriers of opposite sign, which are subsequently collected by two charge selective contacts. For silicon solar cells, [ 1 ] as well as for dye-sensitized solar cells (DCSs) [ 2 ] those collecting electrodes are most commonly located on opposite sides of the junction in a co-planar arrangement, above and below the photoactive junction. Consequently at least one of the electrodes needs to combine transparent and conducting properties, compromising both, optical transmission as well as electrical conductivity. Placing both collecting electrodes onto one common face of the photovoltaic junction provides the opportunity to use opaque electrode materials and to illuminate the junction through the opposite, optically unobstructed face. Such back-contact concepts have successfully been applied to increase the performance of silicon solar cells. [ 3 ] Charge collection in these devices is facilitated by a set of two interdigitated fi nger electrodes, co-located on the backside of the silicon wafer. [ 3 ] In this work we use analogue concepts to construct dye-sensitized back-contact solar cells that use interdigitated electrodes to effi ciently extract photogenerated positive and negative charge carries from an overlying dye-sensitized heterojunction. The potential advantages of BC-DSCs over conventional DSCs are that (1) optical transmission losses can be avoided, (2) highly conductive electrode materials can be used for charge collection, (3) opaque substrate materials can be applied, and (4) auxiliary wiring and interconnections can be integrated onto one common substrate to facilitate the fabrication of interconnected solar cell modules and their integration into electronic circuits. The most common DSC device confi guration is schematically shown in Figure 1a . The DSC electrodes consist of an FTO glass plate coated with a dye-sensitized mesoporous TiO 2 layer and an additional platinized FTO substrate sandwiched together. The cell gap is fi with an electrolyte solution that contains a redox couple such as iodide/triodide. An appropriate spacer thickness ensures that direct contact of the mesoporous TiO 2 and the opposing platinized FTO glass (counter electrode) is avoided. Dye excitation by visible light is generally followed by ultrafast electron injection into the semiconductor electrode (TiO 2 ). These photogenerated electrons show free diffusion