The U.S. Department of Energy's National Renewable Energy Laboratory (NREL) has set a world record in solar cell efficiency with a photovoltaic device that converts 40.8% of the light that hits it into electricity. This is the highest confirmed efficiency of any photovoltaic device to date, NREL says.
The inverted metamorphic triple-junction solar cell was designed, fabricated and independently measured at NREL. The 40.8% efficiency was measured under the concentrated light of 326 suns.
The new solar cell differs significantly from the previous record holder, according to NREL. Instead of using a germanium wafer as the bottom junction of the device, the new design uses compositions of gallium indium phosphide and gallium indium arsenide to split the solar spectrum into three equal parts that are absorbed by each of the cell's three junctions for higher potential efficiencies.
The technology is achieved by growing the solar cell on a gallium arsenide wafer, flipping it over and then removing the wafer. The resulting device is extremely thin and light, and represents a new class of solar cells with advantages in performance, design, operation and cost.
NREL's Mark Wanlass invented the original inverted cell, which recently won an R&D 100 award. 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.