Metamorphic Concentrator Solar Cells with Over 40% Conversion Efficiency

Multijunction III-V concentrator cells have attracted much interest for concentrator photovoltaic (PV) systems recently due to their unparalleled conversion efficiencies. As high as these efficiencies are, they can be made even higher if the combination of subcell bandgaps for the multijunction solar cell are chosen from metamorphic semiconductors that are not all lattice-matched to the same growth substrate. Advances in the design of metamorphic subcells to reduce carrier recombination and increase voltage, wide-bandgap tunnel junctions capable of operating at high concentration, metamorphic buffers to transition from the substrate lattice constant to the active subcells, concentrator cell AR coating and grid design, and integration into 3-junction cells current matched under the terrestrial spectrum have resulted in new heights in solar cell performance. A metamorphic Ga0.44In0.56P/ Ga0.92In0.08As/ Ge 3-junction solar cell from this research has reached a record 40.7% efficiency at 240 suns, under the standard reporting spectrum for terrestrial concentrator cells (AM1.5 direct, low-AOD, 24.0 W/cm 2 25°C), and experimental lattice-matched 3-junction cells have now also achieved over 40% efficiency, with 40.1% measured at 135 suns. This metamorphic 3-junction device is the first solar cell to reach over 40% in efficiency, and has the highest solar conversion efficiency for any type of photovoltaic cell developed to date.