A new world record for the direct conversion of sunlight into electricity has been established by French companies Soitec and CEA-Leti, working with the Fraunhofer Institute for Solar Energy Systems, in Germany. The conversion rate of their multi-junction solar cell was measured at 46%.
Multi-junction cells are used in concentrator photovoltaic (CPV) systems and are best suited to low cost systems in regions with a large amount of direct solar radiation.
It is the second world record achieved by the three companies within a year or so, following after the record announced in September 2013. Fraunhofer considers that it clearly demonstrates the strong competitiveness of the European photovoltaic research and industry.
Multi-junction solar cells are based on a selection of III-V compound semiconductor materials. The world record cell is a four-junction cell, and each of its sub-cells converts precisely one quarter of the incoming photons in the wavelength range
between 300 and 1750 nm into electricity. When applied in a concentrator PV, a very small cell is combined with a Fresnel lens, which concentrates the sunlight onto the cell. The new record efficiency was measured at a concentration of 508 suns and
has been confirmed by the Japanese AIST (National Institute of Advanced Industrial Science and Technology).
A special challenge that had to be met by this cell was the exact distribution of the photons among the four sub-cells. It has been achieved by precise tuning of the composition and thicknesses of each layer inside the cell structure.
Jocelyne Wasselin, Vice President Solar Cell Product Development for Soitec, a producer of high performance semiconductor materials, says: "We are very proud of this new world record. It confirms we made the right technology choice when we decided to develop this four-junction solar cell and clearly indicates that we can demonstrate 50% efficiency in the near future." She added: "To produce this new generation of solar cells, we have already installed a line in France. It uses our bonding and layer-transfer technologies and already employs more than 25 engineers and technicians. I have no doubt that
this successful co-operation ... will drive a further increase in CPV technology efficiency and competitiveness."
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