Advanced Epitaxial Lift-Off Quantum Dot Photovoltaic Devices

We propose to develop a high-efficiency, triple-junction, epitaxial lift-off (ELO) solar cell by incorporating quantum dots (QDs) within the current-limiting subcell. We intend to leverage existing QD epitaxy processes developed by the Rochester Institute of Technology and combine this with MicroLink's expertise in multi-junction cell growth and ELO technology. We will employ QDs to enhance the middle cell absorption in a InGaP/GaAs/InGaAs metamorphic IMM cell. Detailed balance calculations indicate that the triple junction efficiency can be increased to ~42% by reducing the bandgap of the middle cell to ~1.2 eV. The combination of the QD technology with multi-junction ELO technology will be exploited in two ways: i) ELO GaAs cells with QD can be grown into full triple-junction cells and ii) back-surface reflectors on the ELO cells will be used to improve absorption by routing IR light for a second pass through the QD subcell. The relevance of this work to NASA is that it will result in lightweight, high-efficiency, triple-junction solar cells that will have a specific power>500 W/kg. In addition, the use of QDs has been shown to improve radiation tolerance of the photovoltaic device.