Fraunhofer 33.3% Si-MJ Cell Efficiency Record

• Germany's Fraunhofer Institute for Solar Energy Systems (ISE) and the EV Group have achieved a new cell efficiency record of 33.3% for a silicon-based multi-junction solar cell
• They used extremely thin 0.002 mm semiconductor layers of III-V compound semiconductors, bonding them to a silicon solar cell
• Visible sunlight is absorbed in a gallium-indium-phosphide (GalnP) top cell, the near infrared light in the gallium-arsenide (GaAs) layer, and the longer wavelengths in the silicon subcell

Germany's Fraunhofer Institute for Solar Energy Systems (ISE) and the EV Group have developed a new silicon-based multi-junction solar cell. It can convert exactly a third of incident sunlight into electricity. The efficiency of 33.3% they achieved is a new record, according to Fraunhofer.

Previously, the 2 had partnered up and achieved an efficiency of 30.2% in November 2016. In March 2017, they reached 31.3%. This technology has been nominated among the top 3 in the energy category for the GreenTec Awards 2018.

For this R&D work, the team used extremely thin 0.002 mm semiconductor layers of III-V compound semiconductors, bonding them to a silicon solar cell through direct wafer bonding. The thickness of these layers is less than a twentieth the thickness of a human hair. Visible sunlight is absorbed in a gallium-indium-phosphide (GalnP) top cell, the near infrared light in a gallium-arsenide (GaAs) layer, and the longer wavelengths in the silicon subcell.

With this process, the efficiency of solar cells can be significantly increased, they stated. Fraunhofer plans to conduct more research to overcome the challenges of reducing the cost of the III-V epitaxy and the connecting technology with silicon. It aims to make high-efficiency solar PV modules with efficiencies of more than 30% possible in the future.

"The new result shows how material consumption can be reduced through higher efficiencies, so that not only the costs of photovoltaics can be further optimized, but also its manufacture can be carried out in a resource-friendly manner," said Dr. Andreas Bett, director of Fraunhofer ISE,.

The project was financed with support from the European Union within the Nanotandem project and the German Federal Ministry for Economic Affairs and Energy (BMWi).