The figure was achieved with an inverted metamorphic triple-junction solar cell designed, fabricated and independently measured at NREL. The 40.8 percent efficiency was measured under concentrated light of 326 suns.

The triple-junction cell is a candidate for the space satellite market and for terrestrial photovoltaic arrays that use lenses or mirrors to focus sunlight onto the solar cells, according to the researchers.

The new solar cell differs from the previous record holder by using compositions of gallium indium phosphide and gallium indium arsenide instead of a germanium wafer as the bottom junction of the device. The novel design splits the solar spectrum into three parts that are absorbed by each of the cell's three junctions for higher potential efficiencies. This is accomplished by growing the solar cell on a gallium arsenide wafer, flipping it over, then removing the wafer. The resulting device is extremely thin and light and produces solar cells with advantages in performance, design, operation and cost, NREL said.

NREL's Mark Wanlass invented the original inverted cell. His design was modified by a team led by John Geisz that further optimized the junction energies by making the middle junction metamorphic as well as the bottom junction. Metamorphic junctions are lattice mismatched. The material properties of the mismatched semiconductors allows for greater potential conversion of sunlight.

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