a b s t r a c t Recently discovered production techniques allow the synthesis of carbon nanostructured films with large surface areas. The abundance of carbon and the unique properties of these nanostructures, including high transparency and excellent electrical conductivity, make these materials very interesting for photovoltaic applications, in particular in combination with amorphous silicon. We examine the properties of thin carbon nanotube films (buckypaper) and graphene in junctions with undoped amorphous silicon thin films. The observed open-circuit voltages, 390 mV for the carbon nanotube film and 150 mV for graphene, suggest that solar cells with high efficiency can be produced without expensive processing steps like doping, multilayer film deposition in high vacuum, or transparent conducting oxide deposition. The buckypaper cells are stable in ambient conditions for many weeks, at least.