Abstract
One of the key issues in the design and development of a satellite Photovoltaic Assembly (PVA) is the trade-off to be made between the available volume located to the PVA, its mass and the total amount of power that the solar panels have to guarantee to the spacecraft. The development of high-efficiency, flexible, lightweight solar cells is therefore instrumental to the design of future satellites providing enhanced missions and services. Based on the consolidated development of GaAs-based single junction and lattice matched triple-junction solar cells, several research efforts are being pursued worldwide to further increase the efficiency and reduce mass. Promising approaches include thin-film technologies such as Inverted Metamorphic and Epitaxial Lift-Off (ELO), and the use of nanostructures or highly mismatched alloys grown by MBE. We propose here an alternative path towards the development of lightweight GaAs-based solar cells with the potential to exceed the Shockley-Queisser (SQ) limit of single junction cells. Our approach is based on the synergistic combination of thin-film design, quantum dots (QDs) absorption, and photonic nanostructures. Challenges and opportunities offered by the use of QDs are discussed. A cost-effective and scalable fabrication process including ELO technology and nanoimprint lithography is outlined. Finally, a proof-of-concept design, based on rigorous electromagnetic and physics-based simulations, is presented. Efficiency higher than 30% and weight reduction close to 90% - owing to the substrate removal - makes the proposed device to rank record power-to-weight ratio, with the potential to become a cost-effective, attractive option for next generation space solar cells.
Highlights
Today’s industry standard for space solar arrays is provided by triple-junction III-V solar cells on a GaAs or Ge substrate having efficiency of 30%
The development of flexible high efficiency solar cells will enable the design of new solar arrays architectures such as rollable solar arrays or inflatable ones with the possibility to be used in satellites or moon bases
For the sake of illustrating the impact of photon management on the quantum dots (QDs) cell performance, we describe a couple of representative designs: i) a thin-film device combining a nanostructured periodic grating on the top surface with a planar reflector at the rear side; ii) a thinfilm device with planar antireflection coating and a periodic grating on the rear side
Summary
Today’s industry standard for space solar arrays is provided by triple-junction III-V solar cells on a GaAs or Ge substrate having efficiency of 30% In these cells the typical substrate thickness is about 150-200 μm (notice that the useful active device thickness for photovoltaic conversion is less than 5 μm), resulting in an average weight of the bare solar cell close to 90 mg/cm and a power–to weight ratio of about 400 W/kg. There is a strong effort worldwide to develop new III-V cell technologies aiming at higher efficiency and lower mass In these approaches, the wafers only serve as a production template and are removed to obtain genuine thin-film solar cells. Nanostructuring of the thin-film cell may be realized through a cost-effective technology such as Nanoimprint Lithography (NIL) that allows to pattern even subwavelength periodic gratings over large areas
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