Exploring Sustainable Alternatives for Space Solar Cells: A Fraunhofer ISE Innovation
The quest for sustainable space exploration has led to a critical examination of the resources and energy required for satellite power systems. High-efficiency III-V multi-junction solar cells, while excellent in performance, have a significant drawback: their production is resource-intensive and energy-demanding, which clashes with the Green Space sustainability vision. Fraunhofer ISE, in collaboration with the European Space Agency (ESA), is addressing this challenge with an innovative approach.
For decades, III-V solar cells have been the go-to power source for satellites due to their high efficiency and radiation tolerance. However, the manufacturing process involves growing thin semiconductor layers on germanium substrates through epitaxy, followed by specific processes. This method, while precise, is resource-intensive due to the use of germanium, the energy-intensive epitaxial growth, and the subsequent microfabrication steps like photolithography and metal evaporation. These steps are costly, time-consuming, and environmentally demanding.
To tackle this issue, Fraunhofer ISE is developing a mask-and-plate microfabrication approach, a reliable alternative for III-V-based solar cells in space. This method, supported by ESA's Discovery & Preparation element, aims to reduce the reliance on photolithography and metal evaporation, which are major contributors to resource intensity. The team's solution, AlternateSpace, introduces inkjet printing technology, a technique commonly used in the graphics and TV screen industries.
Inkjet printing with hotmelt inks offers several advantages. It avoids toxic or photoactive materials, applies precise patterns directly, and eliminates wet-chemical development steps, simplifying the process and reducing chemical waste. For metal contact deposition, electroplating replaces metal evaporation, allowing for metal deposition only on uncovered semiconductor areas without lift-off steps.
The development process involved extensive optimization, including testing various inks and adjusting parameters like resolution and temperature to ensure reliable small contact openings. The mask's chemical compatibility was verified through hotmelt ink testing across different electrolytes, temperatures, and pH values. The team also evaluated different metal stacks for electroplating, ultimately choosing nickel-phosphorus plating as a non-ferromagnetic alternative to standard nickel, resulting in a space-compatible sample with silver front-side contacts.
The culmination of this effort is a fully functional, photolithography-free solar cell based on space-compatible electroplated metal contacts, expected by December. This achievement marks a significant step towards cost-effective, sustainable, and efficient III-V solar cell technology, paving the way for a scalable and economically viable manufacturing route for next-generation III-V space photovoltaics. According to Erminio Greco, Solar Generators Engineer at ESA, this work highlights the Discovery & Preparation program's role in generating novel ideas for future space technologies.
Fraunhofer ISE's Oliver Höhn emphasizes the simplified process and reduced chemical waste, aligning with Green Space sustainability goals. The team aims to collaborate with industry to further develop, stabilize, and scale the process for industrial realization, showcasing a promising step towards sustainable space exploration.
