Multiple-reuse of Ge Substrates: Towards Cost-effective and Sustainable III-V Solar Cells Fabrication

High efficiency solar cells based on III-V layers on Ge substrates are commonly used for space devices, but their high cost, partly due to Ge substrate, make them less suitable for terrestrial photovoltaic applications. The porous lift-off process offers a solution for detaching a thin, flexible, and lightweight cell and reusing the substrate, potentially making these solar cells more cost-effective. To date, only one reuse of the substrate has been proven. However, further examination of multiple reuse cycles is crucial in understanding the trends in the surface of the wafer over cycles. The HF-based wet chemistry employed in this study, allows for the substrate to be reused three times by removing the broken pillars that remain after each porous lift-off cycle. The reusability of the substrate is guaranteed due to the smooth and blemish-free surfaces with low RMS roughness achieved through reconditioning. Even after three porous lift-off cycles, the epitaxial layer remains monocrystalline with a roughness of only 3 nm, making it suitable for solar cell growth. These findings open up the possibility for a more affordable and sustainable method of producing high efficiency solar cells, reducing costs by a factor of 4 and Ge consumption by a factor of 19 compared to traditional manufacturing methods.