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Testing the new record-breaking solar cell: There are approximately 500 concentrator cells on the 100 millimetre large wafer. They are being individually connected to the concentrator optic and incorporated in the module.
© Fraunhofer ISE/Foto Alexander Wekkeli
Spotlight on research projects: Concentrator photovoltaics
13.01.2015

Basic principle of multiple solar cells: The sub-cells of a triple solar cell that are respectively specialised to a partial range of the solar spectrum complement each other. In doing so, they use a significantly greater proportion of the solar spectrum than a silicon cell.
© Fraunhofer ISE

Quadruple solar cell achieves record-breaking efficiency

Researchers have developed a quadruple solar cell that converts 46 per cent of sunlight into electricity. The high-performance cells achieve this record-breaking efficiency in connection with optics that concentrate the light 508 times. If these cells were built in concentrator modules, energy would be produced even more economically in regions with high levels of sun.

Within one year, researchers from the Fraunhofer Institute for Solar Energy systems ISE, from Soitec – the semi-conductor and CPV specialists – and the French technology research institute CEA have broken their own record.  They improved the efficiency of the quadruple solar cell from 44.7 to 46 per cent. Dr. Jocelyne Wasselin, vice president of the solar cell product development at Soitec, emphasised: “We are very proud of this new world record. It confirms our choice of technology for the development of this quadruple solar cell and at the same time is a clear indication that in the near future we can attain the 50 per cent mark.”

Multiple cells: complex and high-performance

The production of multiple solar cells is expensive and complex, but a very small solar cell area on which the radiation is bundled to the concentrator optics is sufficient. Different semi-conductor materials from groups III and V of the periodic table are combined for the multiple cells. For example, gallium-indium-phosphide, gallium-indium-arsenide and germanium are used. Each of the four stacked semi-conductors is compiled of several individual, functional layers. Each one uses a different wavelength range of sunlight to generate electricity (image on left). In order to achieve optimum efficiency, the four sub-cells stacked over each other are adapted so that exactly the same currents are generated in each one.  Therefore, there is no weakest link that could limit the yield. Each sub-cell converts a quarter of the photons in the wavelength range between 200 and 1,750 nanometre into electricity. The researchers used a complex process to precisely adapt the material composition and thickness of each individual semi conductor layer in the solar cell to achieve this equal distribution of light energy to the four sub-cells.

Concentrated energy from more than 500 suns

Multiple solar cells and concentrator systems are combined into modules for terrestrial use.  In these so-called concentrated photovoltaics, the optics channel the ray of light, which is concentrated from 100 to 1,000, to each pin-head sized solar cell. A tracker is used to enable the module to track the position of the sun. The new record value was measured with a concentration of 508 times the incident light. Correspondingly, the area of the solar cell is also 500 to 800 times smaller than on standard photovoltaics. Concentrator modules are suitable for areas with a high proportion of direct solar radiation, such as Southern Europe. They would be able to generate renewable electricity there economically.

Australians achieve over 40 per cent efficiency

Researchers at the Australian University of New South Wales achieved an efficiency of over 40 per cent in field tests with a different cell structure: On a germanium substrate they combined modern triple solar cells with silicon solar cells, which are cheap to produce. They split the light, which is not used by the triple cells, into different spectral ranges and conduct it to the silicon cells.

The Australian researchers want to use the new record-breaking cells in a tower power plant. In this concept, developed by solar power plant manufacturer RayGen Resources, a range of mirrors, so-called heliostats that track the sun, conduct the radiation and concentrate it on the receiver with solar cells in the tower.

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Project management, cell development
Fraunhofer ISE

Development, semi conductors and CPV
Soitec Solar

Development and technology
CEA / Leti

Service

Energy from a thousand suns
BINE-Projektinfo 02/2014, PDF, 4 pages, 1.3 MB

Innovations in Photovoltaics
BINE-Themeninfo II/2011, PDF, 20 pages, 1.5 MB