Thin Film Solar Cells Fabricated Using Cross-Shaped Pattern Epilayer Lift-Off Technology for Substrate Recycling Applications

This study reports the use of cross-shaped pattern epitaxial lift-off (ELO) technology to release crack-free single crystal epilayers with a solar cell structure from a gallium arsenide (GaAs) substrate. A cross-shaped pattern array was used to define cell size and provide the etch path for the etchant solution. AlAs was used as a sacrificial layer and etched using a hydrofluoric acid etchant through the cross-shaped hole. Results indicate that the entire wafer can be etched simultaneously. The desired carrier, i.e., the electroplate nickel substrate, can directly contact the epilayer without wax or low-viscosity epoxy, and can also be applied to an external force through magnetic attraction to decrease the release time. After the cross-shaped pattern ELO process, the separated GaAs substrate can be recycled through chemical cleaning. The performance of solar cells grown on new and recycled GaAs substrates remained above 90% of the initial performance when the substrate was recycled less than three times.