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Inverted Metamorphic Solar
Cell Sets efficiency Record
Scientists at the U.S. Department of Ener- manium wafer as the bottom junction of the
gy’s National Renewable Energy Labora- device, the new design uses compositions of
tory (NREL) have set a world record in solar gallium indium phosphide and gallium indi-cell efficiency with a photovoltaic device that um arsenide to split the solar spectrum into
converts 40. 8 percent of incident light into three equal parts that are absorbed by each of
electricity. This is the highest confirmed effi- the cell’s three junctions for higher potential
ciency of any photovoltaic device to date. efficiencies. This is accomplished by growing
The inverted metamorphic triple-junc- the solar cell on a gallium arsenide wafer,
tion solar cell was designed, fabricated and flipping it over, then removing the wafer.
independently measured at NREL. The 40. 8 The resulting device is extremely thin and
percent efficiency was measured under con- light and represents a new class of solar cells
centrated light of 326 suns. One sun is about with advantages in performance, design,
the amount of light that typically hits Earth operation and cost.
on a sunny day. The new cell is a natural can- NREL’s Mark Wanlass invented the origi- NReL researcher John geisz with
didate for the space satellite market and for nal inverted cell, which recently won an record-setting IMM PV cell.
terrestrial concentrated photovoltaic arrays, R&D 100 award. His design was modified by
which use lenses or mirrors to focus sunlight a team led by John Geisz that further opti-onto the solar cells. mized the junction energies by making the
The new solar cell differs significantly middle junction metamorphic as well as the line up. The material properties of the mis-from the previous record holder — also based bottom junction. Metamorphic junctions matched semiconductors allow for greater
on an NREL design. Instead of using a ger- are lattice-mismatched — their atoms don’t potential conversion of sunlight.
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