Fraunhofer ISE achieved record module efficiencies of 31.3% and 34.2% using III-V tandem photovoltaic architectures
A 218 cm² III-V silicon tandem module developed under the Mod30plus project reached 31.3% efficiency at module scale
A larger 833 cm² III-V germanium module realized within the Vorfahrt project achieved 34.2% efficiency after terrestrial spectrum adaptation
Commercial crystalline silicon modules are typically rated at around 24% efficiency. The physical efficiency limit of single-junction silicon is approximately 29.4%. Moving beyond this ceiling requires combining semiconductors with different bandgaps in tandem architectures.
Researchers at Germany’s Fraunhofer Institute for Solar Energy Systems ISE have achieved record module efficiencies of 31.3% and 34.2% for III-V tandem PV modules.
The modules are based on semiconductor compounds formed from elements in groups III and V of the periodic table. These materials are widely used in high-efficiency multi-junction solar cells, particularly in space applications.
31.3% III-V Silicon Tandem Module
The first module was developed under the Mod30plus research project. It is a 218 cm² III-V silicon tandem module and achieved 31.3% efficiency.
As part of the project, Fraunhofer ISE realized small-scale production of these tandem cells and adapted them for shingle-based interconnection. The design combines a III-V top cell with a silicon bottom cell in a two-terminal configuration. The layout reduces inactive spacing and limits resistive losses.
The research center previously reported an efficiency of 36.1% for a III-V silicon tandem cell. Translating cell-level performance into a module format constitutes a critical step. Module assembly typically introduces additional optical and electrical losses. Crossing the 31% threshold at the module scale is therefore an important technical milestone.
34.2% III-V Germanium Tandem Module
The second module, developed within the Vorfahrt project, follows a different route. It is based on triple-junction III-V cells grown on germanium substrates.
The 833 cm² module achieved 34.2% efficiency. The cell concept builds on technology originally developed for space applications. The triple-junction cells were further adapted for terrestrial use by project partner AZUR SPACE Solar Power, including alignment to the terrestrial solar spectrum.
Additional optical optimization was implemented at the module level. Project partner temicon GmbH transferred a nano-imprinted surface structure onto the front glass, reducing reflection losses and contributing to the final efficiency result. At 34.2%, the module sets a new benchmark for this class of tandem PV technology.
Conventional silicon modules cannot exceed their single-junction efficiency ceiling. This limitation is one reason tandem research continues to intensify.
“As single solar cells approach their physical limits, replacing them with multiple stacked cells becomes necessary to unlock further efficiency gains,” explained Dr. Laura Stevens, project leader of the Vorfahrt initiative at Fraunhofer ISE.
Although more complex and costlier than silicon-only modules, III-V tandem designs are suited to space-constrained applications where maximum energy yield per square meter is required. This includes building-integrated PV and other high-performance segments.
Both projects were supported by Germany’s Federal Ministry for Economic Affairs and Energy and involved multiple industrial and academic partners.
