Fraunhofer ISE has been working on the ambitious "50 percent" project for two years. Funded by the German Federal Ministry for Economic Affairs and Climate Protection BMWK, the aim is to produce a solar cell with 50 % efficiency for the first time.
To this end, each individual layer of the complex multi-junction solar cells is being further optimized and process technology improvements to the metal contacts and improved anti-reflective layers are being incorporated. The project team has now achieved its first breakthrough: its latest solar cell achieves an efficiency of 47.6% under concentrated sunlight.
"We are thrilled with this result, which was achieved just one year after the opening of our new Center for High Efficiency Solar Cells," says Dr. Frank Dimroth, Head of Department for III-V Photovoltaics and Concentrator Technology at Fraunhofer ISE.
The layer structure of the new solar cell was developed back in 2016 together with the French company Soitec AG, a designer and manufacturer of innovative semiconductor materials. It is an upper tandem solar cell made of gallium indium phosphide (GaInP) and aluminum gallium arsenide (AlGaAs), which was bonded by Soitec to a lower tandem solar cell made of gallium indium arsenide phosphide (GaInAsP) and gallium indium arsenide (GaInAs). The solar cell layers have now been provided with improved contact layers and a 4-layer anti-reflective coating at the Center for High Efficiency Solar Cells at Fraunhofer ISE. This reduces resistance losses as well as reflection on the front side of the cell, which is sensitive in a broad spectral range of 300-1780 nanometers. Conventional silicon solar cells only absorb sunlight up to a wavelength of 1200 nm and therefore do not require such a broadband anti-reflection coating.
