SBIR-STTR Award

Quantum dots are nanoscale materials that have already improved the performance of optical sensors, lasers, light emitting diodes and solar cells. The unique properties of these nanomaterials offer tremendous benefit in developing high efficiency thermophotovoltaic cells as well. Theoretical studies predict a potential efficiency of 63.2% for an array of quantum dots sandwiched between the emitter and base layers in a typical photovoltaic junction. Significant gains can also be expected in the case of thermophotovoltaic cells. We propose an InGaAs TPV cell which incorporates InAs quantum dots to provide sub-gap absorption and thus improve the short-circuit current. This cell could then be integrated into a MIM to achieve a TPV cell whose efficiency would significantly exceed (by about 15% to 20%) current SOA standards. These TPV cells can be used for deep space missions, with a radioisotope thermoelectric generator (RTG) fueled by plutonium-238 as the on-board source of heat.

For NASA deep space science missions, radioisotope thermoelectric generators (RTG) fueled by plutonium-238 are used to provide on-board source of heat, which is then converted to electricity. At present, NASA uses 8% efficient thermoelectric conversion systems. Compound semiconductor thermophotovoltaic (TPV) cells provide an attractive alternative. The highest efficiency TPV cell reported is a 23.6% (radiator at 1039?C, cell at 25?C) InGaAs monolithically interconnected module (MIM) on InP. We proposed an InGaAs TPV cell which incorporates InAs quantum dots to provide sub-gap absorption thus improving its short-circuit current. This cell could then be integrated into a MIM to achieve a TPV cell whose efficiency would significantly exceed (by about 15% to 20%) the state-of-the-art. In Phase I we demonstrated the feasibility of growing InAs quantum dots on 0.6 eV InGaAs on lattice-mismatched InP, and that these quantum dots, when inserted into the TPV cell, extend the bandedge, providing sub-bandgap absorption. In Phase II we propose to optimize the quantum dot structures to improve efficiency of the TPV cells, and integrate them into MIMs to achieve very high conversion efficiencies. Resulting higher specific power and power density of the overall power systems will be of great benefit to NASA in the form of lower launch costs and increased mission capability.