Single crystalline gallium arsenide photovoltaics on flexible metal substrates

Combining the unsurpassed performance of GaAs based multi-junction technologies with a conventional roll to roll processing standards of thin film industry could lead to paradigm-shifting reduction of the cost of solar electricity and increase of specific efficiencies. But thus far, attempts toward the direct deposition of GaAs and related compounds on metal foils have yielded to poorly performing polycrystalline films and devices. Here we report on the fabrication of single crystalline GaAs-based epilayers and solar cells on thin (50 microns) flexible polycrystalline Ni-based metallic substrates. A rapid (1m/hour) roll to roll ion beam assisted deposition is used to deposit oxide based adaptation buffers on the metal substrates followed by a growth of highly textured thin Ge films and the subsequent growth of GaAs epilayers by molecular beam epitaxy. RHEED, X-ray diffraction and transmission electron microscopy analysis confirm the (001) orientation and the single crystalline nature of the GaAs films. The fabricated samples exhibit strong photoluminescence response attesting the optoelectronic quality of the fabricated films and analysis of near band edge excitons confirms minimal (or no) thermoelastic/lattice mismatch strain in GaAs epilayer.