Fraunhofer ISE tandem solar cell hits 47.6% efficiency under 665 suns

The Fraunhofer Institute for Solar Energy Systems ISE on Monday said it has reached 47.6% efficiency with a four-junction solar cell at a concentration of 665 suns.

The work is part of the institute’s "50 Percent" project, whose goal is to develop the first photovoltaic (PV) cell with 50% efficiency. Fraunhofer ISE has been working for two years on the project, with funding from the German climate ministry.

The record 47.6% efficiency at 665 suns has been reached with a tandem cell, bonding an upper solar cell made of gallium indium phosphide (GaInP) and aluminum gallium arsenide (AlGaAs) onto a lower tandem cell made of gallium indium arsenide phosphide (GaInAsP) and gallium indium arsenide (GaInAs).

The layer structure was developed back in 2016 in partnership with French firm Soitec Inc. Fraunhofer ISE applied an improved contact layer and a four-layer antireflection coating at its Center for High Efficiency Solar Cells to reduce the resistance losses and the reflection on the front side of the cell.

"Possible applications of such highly efficient tandem solar cells include concentrator photovoltaic systems, which contribute to efficient power generation in sun-rich countries,” commented Stefan Glunz, division director of Photovoltaics Research at Fraunhofer ISE.

Multi-junction solar cells made of III-V compound semiconductors are among the most efficient PV cells in the world. They reach their highest potential under concentrated sunlight, Fraunhofer ISE explains. Miniature solar cell devices of just a few square millimetres are used in such projects.

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