Nanomaterials for third generation photovoltaics

'Third generation' approaches aim to achieve high efficiency for photovoltaic devices but in such a way as to allow large scale implementation. The way to achieve these goals is to tackle one or both of the two major loss mechanisms in solar cells, that of non-absorption of below bandgap photons and thermalisation of carriers generated by photon energies exceeding the bandgap. The theoretical and practical aspects of several approaches to achieving this through the use of multiple energy levels are considered with reference to the limiting detailed balance efficiencies of ideal devices. Nanostructured materials are of great interest in realising some of these approaches, such as quantum dot superlattices for tandem solar cells and intermediate band cells, nanocrystals for multiple exciton generation cells and highly ordered nanostructures for hot carrier cells.