Fraunhofer ISE achieves record efficiencies for two new tandem PV modules

Scientists at Germany’s Fraunhofer Institute for Solar Energy Systems (ISE) have succeeded in constructing two tandem photovoltaic modules with “record” efficiencies. A III-V germanium PV module with an efficiency of 34.2 percent, incorporating solar cells from Azur Space and anti-reflection structures from Temicon, has become what ISE calls “the most efficient solar module in the world”. A III-V silicon PV module achieves an efficiency of 31.3 percent, setting a record in its class, and is based on established, cost-effective silicon technology.

“Both tandem PV technologies have the potential to fill application gaps between conventional, cost-effective ground-mounted and rooftop systems on the one hand, and high-performance but more expensive space solar cells on the other,” said Prof. Dr. Andreas Bett, Director of ISE. “III-V in tandem with silicon as a more affordable option, III-V on germanium as a slightly more efficient alternative, are both interesting technology routes for integrated PV applications wherever space is limited.”

A few years ago, researchers at the Fraunhofer ISE achieved a new efficiency record for silicon-based solar cells with a III-V silicon solar cell reaching 36.1 percent. As part of the research project Mod30plus, they have now, for the first time, realized a small-scale production of these solar cells, adapted for interconnection with shingle technologies. A module produced by the research team in this way, measuring 218 cm2, has now achieved a record efficiency of 31.3 percent.

A 833 cm2 tandem module with an efficiency of 34.2 percent was built by a second research team from Fraunhofer ISE as part of the "Vorfahrt" project. It consists of triple III-V germanium cells, which the project coordinator AZUR SPACE Solar Power further developed for the new module technology. For this purpose, the solar cell manufacturer adapted its triple solar cell technology to the terrestrial solar spectrum, so that it can now be produced in comparable quantities and in the same wafer formats as space solar cells. Temicon GmbH further improved the module's efficiency through a stochastic surface structure transferred onto the glass surface using nano-imprint, which minimizes reflection losses at this interface of the record module.

Conventional silicon solar cells cannot exceed a physical efficiency limit of 29.4 percent; currently commercially available PV modules already have efficiencies around 24 percent. "That is why we are conducting intensive research to replace single solar cells with multiple solar cells in modules,”ISE record said Dr. Laura Stevens, scientist at Fraunhofer ISE and project leader of Vorfahrt. “The fact that we achieved a world record with the III-V germanium module shows the great potential in combining multiple semiconductors,” she said.

“Tandem photovoltaics is one of the fastest-growing research fields in solar research today,” said Dr. Jonas De Rose, project leader of Mod30plus.