High-Efficiency, Radiation-Hard, Lightweight IMM Solar Cells

Future NASA exploration missions require high specific power (>500 W/kg) solar arrays. To increase cell efficiency while reducing weight and maintaining structural integrity, we propose an approach to cell design that involves the use of quantum dots and epitaxial lift-off. In the near term, this approach will allow us to improve on what are currently the best space solar cells available in terms of efficiency and material properties for space utilization. In the proposed Phase I project, MicroLink and its collaborator, Rochester Institute of Technology, will incorporate InAs quantum dots (QDs) in the InGaAs subcell of an InGaP/GaAs/InGaAs triple-junction solar cell to increase radiation tolerance and efficiency, thereby improving end-of-life performance of the solar cell by >5%. By incorporating quantum dots into the InGaAs third cell, we will also extend the wavelength absorption range of InGaAs cell to beyond 1,250 nm, thereby increasing the current produced in the bottom subcell. The quantum dot-enhanced subcell will be the last grown solar cell in an inverted metamorphic (IMM) format on GaAs and will be compatible with MicroLink's epitaxial lift-off (ELO) process. Innovative light management techniques such as reflective metal back contact will be employed to increase absorption in the solar cell by promoting photon recycling.

The improved radiation tolerance and temperature coefficients will open the design space for NASA-specific missions such as low-light-intensity missions to the Jupiter system or high-light-intensity missions near Mercury and the Sun. Solar panels made up of quantum-dot-embedded triple-junction epitaxial lift-off (ELO) solar cells are lighter than those containing conventional solar cells, and the high specific power will make them suitable for the requirements of solar electric propulsion (SEP) applications. Furthermore, cost reduction factors such as the substrate reuse achievable with ELO solar cells make them more attractive for applications that require a large number of panels.

Potential non-NASA applications include spacecraft, unmanned aerial vehicles (UAVs), and terrestrial energy collection. In spacecraft applications, the proposed cells are a suitable replacement for existing solar cells and will enable spacecraft power generation using higher specific power solar panels. The proposed cells are an enabling technology for large-scale solar electric propulsion (SEP) spacecraft. In UAV applications, the proposed cells can act as a supplement to battery power for endurance enhancement. High efficiency, lightweight cells this type are an enabling technology for high altitude, long endurance (HALE) UAVs such as DARPA Vulture. In terrestrial applications, the proposed cells can be used in solar sheets for generation of electricity for off-grid applications, e.g., military field deployments, civilian outdoors and camping, and supplementary power for mobile devices such as phones.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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