WORLDNEWS
Fraunhofer researcher for the “Fondation Louis D” award
THE power of the sun can help to keep us supplied with sufficient energy in the future. The concentrated power of the sun recently also helped a young German scientist earn the “Fondation Louis D” award, the highest-endowed award presented in France for achievements in science. Dr. Frank Dimroth of the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg has developed multi-junction solar cells with record efficiency levels.
In the quest for economically feasible solar energy, teams of researchers worldwide are working to develop solutions that will lower production costs and increase efficiency levels for converting sunlight to electricity. One outstanding variation has been developed by Dr. Frank Dimroth and his team: a metamorphic triple-junction solar cell. It can convert more sunlight to electricity than many other solar cells, reaching a record efficiency of 41.1%.
To accomplish this, researchers created a multi-junction solar cell made of III-V compound semiconductors by stacking three single-junction cells on top of each other, each one particularly efficient in converting a limited spectral bandwidth of sunlight to electricity. The result: efficiency levels that nearly double the efficiency of conventional silicon-based solar cells.
“I am extremely pleased for my team and the entire Institute in light of this outstanding research prize and the international recognition it brings for our work,” Dimroth stated. “This prize shows that we are on the right track toward developing solar technologies.”
A multi-junction solar cell is created with the aid of processes similar to those used in the semiconductor industry. “Our work involves a modern epitaxial process known as metal organic vapour phase epitaxy,” Dr. Dimroth explained. The process involves successively depositing
solar sub-cells on top of each other on a substrate of germanium. The result is a wafer-thin solar cell structure just a few µm thick, with a well-hidden complex inner structure of up to 50 monocrystalline layers. With the development of
metamorphic crystal growth,
Frank Dimroth and his colleagues have made it possible to use a larger range of III-V compound semiconductors to grow multi-junction solar cells. This makes the solar cells better adapted to the spectrum of wavelengths found in sunlight.
To date, multi-junction solar cells have been used in space technology to supply satellites with energy. To tap into the high potential efficiencies for regenerative power generation here on earth, Frank Dimroth and his colleagues came up with a special design. They developed a photovoltaic concentrator module that uses Fresnel lenses to concentrate solar radiation by a factor of 500 onto triple- junction solar cells only 3 mm2 in area. This reduces the costly semiconductor surface area required and makes III-V multi-junction solar cells for electricity generation an attractive alternative in regions rich in direct sunlight.
Following his undergraduate degree in Zurich, Frank Dimroth began doctoral studies at the Fraunhofer ISE in the area of experimental physics and received his Ph.D. in 2000 at the University of Constance. Very early on, he was successful in the field of semiconductor epitaxy, and in 2007 he was named manager of the group “III-V Epitaxy and Solar Cells,” a group currently with 50 employees.
Over the past ten years Dimroth and Dr. Andreas Bett, deputy director of ISE, have worked with III-V multiple-junction solar cells and CPV. In 2005 they established Concentrix Solar a spin-off of the Institute. The company produces concentrator photovoltaic systems.
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www.solar-pv-management.com Issue III 2010
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