Due to the high cost of silicon photovoltaics there is currently great interest in fi nding alternative semiconductor materials for light harvesting devices. Single-walled carbon nanotubes are an allotrope of carbon with unique electrical and optical properties and are promising as future photovoltaic materials. It is thus important to investigate the methods of exploiting their properties in photovoltaic devices. In addition to already extensive research using carbon nanotubes in organic photovoltaics and photoelectrochemical cells, another way to do this is to combine them with a relatively well understood model semiconductor such as silicon. Nanotube-silicon heterojunction solar cells are a recent photovoltaic architecture with demonstrated power conversion effi ciencies of up to ̃ 14% that may in part exploit the photoactivity of carbon nanotubes.