Researchers from the Fraunhofer ISE’s Center for High-Efficiency Solar Cells claimed to have achieved a power conversion efficiency of 47.6% in a multijunction solar cell (III-V) using an anti-reflection coating at a concentration of 665 suns (heat concentration levels equalling 665 suns).

The results presented at the second International TandemPV Workshop, Germany, are the outcome of Fraunhofer ISE’s two-year-long research titled ’50 Percent’. The ISE scientists optimized each layer of the complex solar cell with multiple junctions, achieving improved process technology incorporated for metal contacts and anti-reflection layers.

The work started in 2016 when ISE experts first introduced the layer structure of a new solar cell in collaboration with the French company Soitec Inc., which designs and develops innovative semiconductor materials used in renewable equipment. The current ISE research improved the solar cell structure developed previously, establishing a much more stable contact layer by applying a four-layer anti-reflection coat to the tandem cell structure.

The German Federal Ministry for Economic Affairs and Climate Action BMWK funded the research to develop the new solar cell with an efficiency of 50%, a global milestone.

In 2016, it was observed that the upper tandem solar cell in Fraunhofer’s experiment is made of gallium indium phosphide (GaInP) and aluminum gallium arsenide (AIGaAS). The experts at Soitec Inc. bonded GaInP and AIGaAS onto a lower tandem solar cell made of gallium indium arsenide phosphide (GaInAsP) and gallium indium arsenide (GaInAs).

The current silicon solar cells have a sunlight absorption wavelength of 1,200 nm. The new research reduced the resistance and reflection losses on the front side of the cell using the anti-reflection coating. The researchers discovered that their multijunction solar cell (III-V) is spectrally sensitive and has a broad sunlight absorption wavelength of 300 nm and 1,780 nm.

Multi-junction solar cells function potentially when lenses concentrate the incoming sunlight onto smaller solar cell devices measuring just a few square millimeters in size. Tandem photovoltaics help overcome the limitations of single-junction solar cells and would further lower the cost of solar power, according to Stefan Glunz, the division director of Photovoltaics Research at Fraunhofer ISE.

Scientists worldwide have been working to improve solar cell power conversion efficiency. A team of researchers from the National Renewable Energy Laboratory also used gallium arsenide with quantum wells and invented a multijunction solar cell. The solar cell in the NREL experiment achieved a record power conversion efficiency of 39.5% under 1-sun global illumination.

In another research project by Fraunhofer ISE, scientists developed a new laser techniqueFoilMet to reduce the amount of silver used in the production of solar panels. The technique interconnects the neighboring solar cells in a module using a thin strip of aluminum foil. It was observed that the process hardly took less than a tenth per wafer per second.