Epitaxial lift-off of GaAs thin-film solar cells followed by substrate reuse

Abstract

We demonstrate the fabrication of GaAs thin-film solar cells on plastic substrate by combining epitaxial lift-off (ELO) and cold weld bonding. A lattice-matched epitaxial protection layer is employed to preserve the wafer surface during the ELO process to enable multiple reuses of the parent wafer. For the removal of protection layer and contaminants from ELO process, we have developed a unique pre-cleaning process. Combination of these technologies enables 1) the fabrication of light weight, flexible thin-film GaAs solar cells, 2) a transfer process that cold-weld bonds the GaAs epi-cell onto an accepting plastic foil substrate, and 3) the multiple growths from a single parent substrate the requires no destructive mechanical polishing process. The morphology and chemistry of the GaAs substrate surface after ELO simulation and protection-layer removal are compared to those of the original substrate using atomic force microscopy, energy dispersive spectrometry, X-ray photoelectron spectrometry and reflection high energy electron diffraction. The regrown epitaxial film quality is investigated by Hall-effect and photoluminescence measurements, and cross-sectional transmission electron microscopy. We show that p-n junction GaAs solar cells grown on original and reused wafers have power conversion efficiencies of ~23%, under simulated AM1.5G illumination. The ability to perform multiple growths from a single parent wafer promises to dramatically reduce production costs for high power conversion efficiency GaAs solar cells.