04/12/2025
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Since the late 1990s, high-efficiency III-V multi-junction solar cells have become the standard for satellite power systems due to their excellent efficiency and radiation tolerance. However, their production is resource- and energy-intensive, which conflicts with Green Space sustainability goals.
While material-efficient fabrication of terrestrial silicon solar cells is already commercially mature, such processes are generally incompatible with the harsh conditions of the space environment. To address this challenge, Fraunhofer ISE, supported by ESA’s Discovery & Preparation element, is developing a mask-and-plate microfabrication approach as a reliable alternative manufacturing method for III-V based solar cells for space applications.
For more than 30 years, III-V solar cells have become the standard power source for satellites thanks to their high efficiency and strong radiation tolerance compared with silicon-based solar cells.
These devices are fabricated by growing very thin semiconductor layers on germanium substrates using a process called epitaxy. After the layers are grown, the cells are manufactured using specific processes. This precise manufacturing approach is compatible with the harsh conditions in space, but it is resource and energy intensive, which clashes with Green Space sustainability goals.
This resource intensity stems from three main factors: the reliance on germanium (Ge) as the substrate; the energy-intensive epitaxial growth process; and the subsequent microfabrication, which involves photolithography and metal evaporation steps – both costly, time-consuming, and energy-demanding steps.
Promising work is underway to enable substrate re-use and efforts are targeting more efficient epitaxial processes. However, microfabrication is not really tackled yet for space solar cells. While material-efficient technologies are already available for conventional terrestrial silicon solar cells production, the requirements for space solar cells usually prevent their implementation, as some materials used in these technologies are incompatible with the reliability needs of the space environment.
A team from Fraunhofer ISE is developing an innovative mask-and-plate approach to microfabricate III-V space solar cells without the use of photolithography or metal evaporation, a solution supported by the European Space Agency through its Discovery & Preparation element. The idea was submitted via ESA’s Open Discovery Ideas Channel (OSIP).
A solution based on inkjet-printing technology
AlternateSpace, the solution developed by the team, is a compelling alternative that addresses sustainability concerns by replacing photolithography with inkjet printing technology, a technique that is well-established in the graphics and TV screen manufacturing industries.
The use of hotmelt inks in this process offers several advantages: the technique does not rely on toxic or photoactive materials, it can be applied directly in a precisely controlled pattern and it eliminates wet-chemical development steps, significantly simplifying the process chain and reducing chemical waste.
For metal contact deposition, this innovative approach also replaces metal evaporation with electroplating. This allows metal to be deposited only on areas where the semiconductor material is not covered by ink with no subsequent lift-off steps required.
This alternative solution required extensive optimisation, including testing various inks and adjusting parameters, such as resolution and temperature, to achieve reliable small contact openings. The mask’s chemical compatibility was verified by testing the hotmelt ink across different electrolytes, temperatures and pH values.
The subsequent metallisation involved the evaluation of different metal stacks for electroplating and explored nickel-phosphorus plating as a non-ferromagnetic alternative to standard nickel. A final sample featuring silver front side contacts on nickel-phosphorus emerged as a space-compatible option.
Towards fully functional thin-film space solar cells
After a fully defined process route that incorporates all the newly developed steps, a fully functional photolithography-free solar cell based on space-compatible electroplated metal contacts is expected in December.
“This work marks a key step toward cost-effective, sustainable and efficient III-V solar cell technology. It paves the way for a scalable and economically viable manufacturing route for next-generation III-V space photovoltaics. The results of the activity highlight the key role of ESA’s Discovery & Preparation programme in generating novel ideas that can drive the development of future space technologies”, commented Erminio Greco, Solar Generators Engineer at the European Space Agency.
“By replacing photolithography and metal evaporation with scalable inkjet printing and electroplating, Fraunhofer ISE demonstrates a simplified process with significantly reduced chemical waste. This approach aligns with the goals of green space sustainability and cost reduction. After the successful demonstration of this approach, we aim towards a collaboration with industry to further develop, stabilise and finally scale the process towards industrial realisation”, commented Oliver Höhn, Head of the III-V Semiconductor Technology Group at Fraunhofer ISE.