PVTIME - Scientists at the National Renewable Energy Laboratory (NREL)
have fabricated a solar cell with an efficiency of nearly 50%.
The six-junction solar cell now holds the world record for
the highest solar conversion efficiency at 47.1%, which was measured under
concentrated illumination. A variation of the same cell also set the efficiency
record under one-sun illumination at 39.2%.
“This device really demonstrates the extraordinary
potential of multijunction solar cells,” said John Geisz, a principal scientist
in the High-Efficiency Crystalline Photovoltaics Group at NREL and lead author
of a new paper on the record-setting cell.
The paper, “Six-junction III-V
solar cells with 47.1% conversion efficiency under 143 suns concentration,”
appears in the journal Nature Energy. Geisz’s co-authors are NREL scientists Ryan
France, Kevin Schulte, Myles Steiner, Andrew Norman, Harvey Guthrey, Matthew
Young, Tao Song, and Thomas Moriarty.
To construct the device, NREL researchers relied on III-V
materials—so called because of their position on the periodic table—that have a
wide range of light absorption properties. Each of the cell’s six junctions
(the photoactive layers) is specially designed to capture light from a specific
part of the solar spectrum. The device contains about 140 total layers of
various III-V materials to support the performance of these junctions, and yet
is three times narrower than a human hair. Due to their highly efficient nature
and the cost associated with making them, III-V solar cells are most often used
to power satellites, which prize III-V’s unmatched performance.
On Earth, however, the six-junction solar cell is
well-suited for use in concentrator photovoltaics, said Ryan France, co-author
and a scientist in the III-V Multijunctions Group at NREL.
“One way to reduce cost is to reduce the required area,” he
said, “and you can do that by using a mirror to capture the light and focus the
light down to a point. Then you can get away with a hundredth or even a
thousandth of the material, compared to a flat-plate silicon cell. You use a
lot less semiconductor material by concentrating the light. An additional
advantage is that the efficiency goes up as you concentrate the light.”
France described the potential for the solar cell to exceed
50% efficiency as “actually very achievable” but that 100% efficiency cannot be
reached due to the fundamental limits imposed by thermodynamics.
Geisz said that currently the main research hurdle to
topping 50% efficiency is to reduce the resistive barriers inside the cell that
impede the flow of current. Meanwhile, he notes that NREL is also heavily
engaged in reducing the cost of III-V solar cells, enabling new markets for
these highly efficient devices. The U.S. Department of Energy Solar
Energy Technologies Office funded the research.
NREL is the U.S. Department of Energy's primary national
laboratory for renewable energy and energy efficiency research and development.
NREL is operated for the Energy Department by The Alliance for Sustainable