Thin-film InAs/GaAs quantum dot solar cells layer-transferred onto Si substrates and flexible plastic films

Thin-film InAs/GaAs quantum dot solar cells on mechanically flexible plastic films are fabricated. A 4.1-μm-thick compound semiconductor photovoltaic layer was grown on a GaAs substrate, and then transferred onto a plastic film through a bonding technique. Our bonding scheme is mediated by a metal-epoxy agent for the realization of bonding at low temperatures (below 200 °C), enabling the use of plastic materials as support substrates, as well as preventing the degradation of the semiconductor photovoltaic layers including quantum dots. We also fabricated thin-film InAs/GaAs quantum dot solar cells on Si substrates, as alternative low-cost, lightweight, robust substrates, using the same layer-transfer scheme. The open-circuit voltages of the transferred thin-film cells are equal to that of the as-grown bulk cell on a GaAs substrate, indicating that no material degradation occurs during our bond-and-transfer process. Furthermore, our transferred thin-film cells exhibit larger photocurrents than the bulk reference and thus higher efficiencies because of the efficient carrier collection in the thin-film photovoltaic layers and enhanced optical path length due to the metallic back reflectors implemented on the support substrates. Our successful fabrication of thin-film quantum dot solar cells on both plastic films and Si substrates is a strong demonstration of the validity of our bond-and-transfer scheme for the formation of thin-film photovoltaics on any kind of support plate or film without degradation, and thus provides a pathway for the production of lightweight, mechanically flexible, low-cost and highly efficient quantum dot solar cells based on ultrathin single-crystalline III-V semiconductors.