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A new record in efficiency for a solar cell of 41.1% for the conversion of sunlight into electricity reported by German researchers is a step forward for photovoltaics.

The solar cell devised by the team at the Fraunhofer Institute for Solar Energy Systems ISE in Frieburg is based on III-V semiconductor materials and consists of thin layers of gallium indium phosphide (Ga0.35In0.65P) and gallium indium arsenide (Ga0.83In0.17As layers) on a germanium (Ge) substrate.

This particular combination of materials enabled the researchers to construct a solar cell that is perfectly matched to the solar spectrum. The multi-junction devices managed to achieve the highest ever efficiency of 41.4% at a sunlight concentration factor of 454.

“The high efficiencies of our solar cells are the most effective way to reduce the electricity generation costs for concentrating PV systems,” says Andreas Bett of the Fraunhofer.

The semiconductor materials used in the new solar cells have long attracted interest for this application because of their potential for high efficiencies but are difficult to grow.

Because atoms in the materials are different distances apart it is difficult to grow layers on top of each other without introducing mistakes in the atomic arrangement – or crystal lattice – known as defects or dislocations.

In working solar cells, defects act as traps or sinks for incoming sunlight and prevent its conversion into electricity.

The Fraunhofer team get around this obstacle by using a trick called metamorphic growth which contains the defects that arise during the growth of the semiconductor materials to regions of the solar device that are not electrically active.

The Fraunhofer ISE is now working with German companies Azur Space and Concentrix Solar to commercialise the technology.

“We want that photovoltaics becomes competitive with conventional methods of electricity production as soon as possible. With our new efficiency results, we have moved a big step further towards achieving this goal,” says Bett.

For further information:
www.ise.fhg.de/
www.azurspace.com/
www.concentrix-solar.de/