Diametric strategies for ultra-efficient photovoltaics

Recent advances from two diametric approaches for realistically approaching the fundamental limits to solar cell conversion efficiency, which follow from basic thermodynamics, will be presented. One relates to a new concept in cell architecture for concentrator photovoltaics, with the possibility of using exclusively indirect bandgap semiconductors (including Si and Ge) at irradiance values of thousands of suns. The second constitutes the first experimental demonstration of performance enhancement by recycling photon emission from high-efficiency non-concentrator (one-sun) solar cells. An analysis of the results points to roadmaps for future improvements.