Fraunhofer ISE achieves world record for concentrator solar cells

Based on a six-year-old development by Freiburg, Germany-based Fraunhofer Institute for Solar Energy Systems ISE and French semiconductor specialist Soitec S.A., a team at ISE’s Center for Highest Efficiency Solar Cells has succeeded in producing a solar cell with 47.6 percent efficiency at 665 suns (665 times solar concentration).
It is a cell with four pn junctions (four-junction cell) based on semiconductors made of elements from the third and fifth main groups of the periodic table (III-V semiconductors). The previous world record for such cells was 46.1 percent. This makes the development presented by ISE at the »2nd International tandemPV Workshop« (May 30 to June 1 in Freiburg) currently the most efficient solar cell worldwide. However, since concentrator cells depend on precise two-axis tracking due to the connected optical system and are costly to manufacture, especially when III-V semiconductors are used, they do not play a role in commercial applications.
The layered structure of the world-record cell was developed by ISE and Soitec in 2016. An upper tandem solar cell made of gallium indium phosphide (GaInP) and aluminum gallium arsenide (AlGaAs) was connected by Soitec to a lower tandem solar cell made of gallium indium arsenide phosphide (GaInAsP) and gallium indium arsenide (GaInAs). This structure has now been optimized with improved contact layers and a new, four-layer anti-reflective coating. While normal solar cells absorb light in a spectral range of up to about 1,200 nanometers, the spectrum of the ISE quadruple cell ranges from 300 to 1,780 nanometers. Accordingly, reflections in this broad band must also be avoided, which places special demands on the anti-reflective layer.
The development was carried out as part of the »50 percent« project funded by the German Federal Ministry of Economics and Climate Protection (BMWK), which aims to produce a solar cell with 50 percent efficiency.

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