Demonstration of Multiple Substrate Reuses for Inverted Metamorphic Solar Cells

The substrate typically accounts for more than 50% of the bill of materials cost for a III-V solar cell wafer. A substantial fraction of this cost can be mitigated via multiple reuses of the substrate. We report on inverted metamorphic (IMM) solar cells grown on GaAs substrates that have undergone up to five consecutive reuse cycles. The active solar cell layers are removed from the substrate after each growth cycle via epitaxial lift-off, which is a nondestructive selective etch process, and the substrate is then repolished in preparation for reuse. The solar cell wafer is transferred to a temporary carrier for processing using standard photolithographic techniques. Data from five reuse cycles demonstrate that the use of repolished substrates does not compromise the performance of IMM solar cells.