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Researchers at the US Department of Energy’s National Renewable Energy Laboratory (NREL) in Golden, CO have set a world record for solar cell conversion efficiency of 40.8%.
The inverted metamorphic triple-junction solar cell was designed, fabricated and independently measured at NREL. The efficiency was measured under concentrated light of 326 suns. The new cell is a candidate for the space satellite market and for terrestrial concentrated photovoltaic (CPV) arrays, which use lenses or mirrors to focus sunlight onto the solar cells.
NREL says that the new solar cell differs significantly from the previous record holder (with an efficiency of 40.7%, achieved in late 2006), which was produced under subcontract by Boeing Spectrolab, based on an NREL design. The new design uses gallium indium phosphide (GaInP) and indium gallium arsenide (InGaAs) to split the solar spectrum into three equal parts that are absorbed by each of the cell’s three junctions, giving higher potential efficiencies. But instead of using a germanium wafer as the bottom junction of the device, the solar cell structure is grown on a gallium arsenide wafer, before inverting it, and then removing the wafer. The resulting device is extremely thin and light, with advantages in performance, design, operation and cost, NREL claims.
Graphic courtesy of NREL.
NREL’s Mark Wanlass invented the original inverted cell. His design has been modified by a team led by John Geisz, which further optimized the junction energies by making the middle junction metamorphic as well as the bottom junction. The material properties of the mismatched semiconductors allows greater potential conversion of sunlight. NREL spokesman George Douglas says that the new device still has room for improvement.
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