Photovoltaics are regarded by many as the most likely candidate for long term sustainable energy production, yet their implementation has been restricted by the high costs involved. Nevertheless, the theoretical limit on photovoltaic energy conversion efficiency, above 85%, suggests that there is room for substantial improvement of present commercially available solar cells, both silicon and thin-film based. Current research efforts are focused on implementing novel concepts to produce a new generation of low-cost, high-performance photovoltaics that make improved use of the solar spectrum