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Multijunction III-V solar cells nominated for German Future Prize

The successful development and market launch of Indium gallium phosphide, indium gallium arsenide and germanium based solar cells by Azur Space, Soitec and Fraunhofer ISE have been acknowledged.

Hansjörg Lerchenmüller, Andreas Bett and Klaus-Dieter Rasch have been nominated for the German Future Prize.

Together they have developed special solar cells, modules and systems that can convert twice as much sunlight into electrical energy as silicon based Photovoltaic systems. The technology uses the following principle: multijunction solar cells that capture different ranges of the solar spectrum are combined with lenses that concentrate the sunlight.

Today, this combination is well-established around the world as concentrator technology. Along with silicon technology and thin-film technology for rooftop or ground-mounted power plants, concentrator technology plays an important role in large power plants situated in sunny regions.

Every year, the jury of the German Future Prize nominates three teams that, thanks to their excellent research, have successfully introduced new products to the market. The Federal President of Germany, Christian Wulff, attended the official nomination ceremony on August 27, 2011 at the IdeenExpo in Hannover and will present the award to the winning team on December 14.

Currently, 85 percent of all photovoltaic modules are made using crystalline silicon. However, this semiconductor material only converts a specific range of the solar spectrum into electrical energy. As a result, the efficiency of the modules is limited.

This is why, 15 years ago, researchers at Fraunhofer ISE decided to dedicate themselves to finding a new approach: They stacked several layers of various semiconductors in one solar cell. In these tiny solar cells, which measure just 3 mm in diameter, semiconductors from groups III and V of the periodic table (InGaP, InGaAs and germanium) are deposited on top of one another. “Each semiconductor captures a different range of the solar spectrum and the energy yields add up,” says Andreas Bett, director of the Materials – Solar Cells and Technology division and deputy director of Fraunhofer ISE.

Multijunction solar cells were initially developed for space applications. The III-V solar cells developed at Fraunhofer ISE are industrially manufactured by Azur Space and used to supply energy for telecommunications satellites. However, the company also specialises in the cost-effective production of multijunction solar cells for terrestrial applications. The III-V solar cells developed at Fraunhofer ISE boast an efficiency of 41.1 percent (a world record in 2009) and are currently being transferred to series production by Azur Space. “Within a very short period of time we were able to show that efficiencies of 40 percent are possible in the solar industry and we believe that those around the 50 percent mark are also entirely feasible,” says Klaus-Dieter Rasch, managing director of Azur Space Solar Power GmbH in Heilbronn.

In order to exploit the potential of multijunction solar cells for terrestrial applications, researchers at Fraunhofer ISE focused their attention on optical concentration. Special lenses that concentrate sunlight by a factor of 500 were placed in front of the multijunction solar cells; cells and lenses were then combined in one module.

 “We have replaced expensive semi-conductor materials and added low cost lenses. Thanks to these newly developed concentrator modules, we are able to produce a higher output per area,” says Bett.

After developing the module in the laboratory, the next step was industrial production. In order to develop production-ready concentrator modules and convert them into high-performance systems,employees at Fraunhofer ISE founded a spin-off company under the direction of Hansjörg Lerchenmüller – Concentrix Solar GmbH.

The newly founded company continued to drive forward the industrial processing technology which had been initiated at Fraunhofer ISE and, after a few years, introduced Concentrix Modules to the market. Today the company is part of Soitec, an international market leader in the semi-conductor industry, and ranks among the world’s leading companies in the field of concentrator technology.

“Our concentrator modules convert 28 percent of sunlight into electricity, that’s twice as much as in conventional photovoltaics,” says Hansjörg Lerchenmüller, Senior Vice President at Soitec. In addition to their lower energy generation costs, concentrator systems have further advantages: Thanks to their modular design they can be used in power plants with energy outputs ranging from less than 1 MW to over 100 MW. The energy needed to manufacture the modules is paid back after just a few months of operation and the investment costs required to set up mass production facilities are comparatively low.

Concentrator technology is well suited for large scale solar power plants located in sunny regions. Soitec Solar has already installed a capacity of more than 3 MW in power plants in Southern Europe, South Africa and the USA and will shortly build another module factory in the US. For all three partners, nomination for the German Future Prize is a tribute to their collective work.

Indeed, the continuous development of concentrator technology is founded both on the many years of collaboration (in research and industry) that the trio has behind them and on their collaboration in years ahead. With their expert knowledge in the field of solar cells, modules and systems, all three partners contribute to the development of a continuously innovative technological process.

Nominated for the German Future Prize 2011, from left to right: Klaus-Dieter Rasch, Managing Director of Azur Space Solar Power GmbH, Hansjörg Lerchenmüller, Senior Vice President at Soitec,  Andreas Bett, Director of the Materials – Solar Cells and Technology Division and Deputy Director of Fraunhofer ISE.
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