Reduce the amount of Germanium used or lost during the production of spacecraft solar panels.

Today, Ge is used as a growth template for III-V based solar cells and also serves as the lowest active junction. While the thickness of the Ge on solar cell level is around 140µm, actually only 10-20µm are really active. Therefore, in order to become thinner and lighter, solar cell manufacturers start to thin down the Ge wafers after cell processing by grinding, etching or lift-off processes (to reduce weight). However, this Ge waste is today not recovered since no economical process exists. Therefore, one idea to improve the use of Germanium is to effectively recover the Ge and assure a cost effective recycling stream. Another possibility to become lighter and reduce the amount of Ge is to start from a different growth template such as e.g. Silicon (Si) that is one of the most abundant materials on earth. Furthermore, it is s also cheaper and lightweight. However, Si wafers are not compatible for growing III-V solar cells directly on them. Therefore, a dedicated development is needed for that option or equivalent alternatives. In previous LCA studies, Germanium (Ge) has been identified as one of the major environmental hotspots of ESA’s space missions. Ge is one of the Critical Raw Materials and the use of it (mainly driven by the solar cells) is the major contributor for the impact of the spacecraft in mineral resource depletion. Even though recycling processes exist to a certain extent (as a minimum within the Ge wafer manufacturer UMICORE) other Ge waste, e.g. Produced during the grinding process when solar cells are thinned, is today not fully recovered.This activity is an important step to mitigate the environmental impact of ESA space missions. This activity encompasses the following tasks:1. Recyclinga. Evaluate recycling concepts with regard to feasibility, ecology and economyb. Identify the best concept and carry out practical testsc. Specify a recycling unit and implement the system into the production line2. Investigate options to improve use of Ge such as Virtual substrate (e.g. Ge on Si substrate).a. Develop buffer layer to grade the virtual substrate, e.g. From Si to Geb. Develop Ge growth on virtual substratec. Growth of III-V solar cell structures on virtual substrates.d. Engineering tests on solar cell structuresA Life Cycle Assessment of the two options (Recycling and Virtual substrate) need to be performed. A comparison of these alternatives with current technology and manufacturing processes is required.