Development of Advanced Anti-Reflection Coatings for High Performance Solar Energy Applications

MicroLink and its subcontractor Magnolia Solar will develop and demonstrate advanced anti-reflection coating (ARC) designs that will provide a better broadband and angular response than that of current coatings. Advanced coatings of this nature are needed to realize the full potential forthcoming generation of multi-junction solar cells that will contain four or more junctions. We will undertake several approaches to this problem: * investigate new dielectric materials that will allow a refractive index intermediate between those of the materials that are currently in common use as ARCs; * investigate a dielectric codeposition processes that will allow the fabrication of materials with a wide range of refractive indices; and * investigate oxidation of Al-containing III-V semiconductor compounds as a mechanism for forming a more transparent window layer. Based on the results of these investigations, we will fabricate and test on III-V triple-junction solar cells the best-identified candidates for improved anti-reflection coating. If successful, the new coating designs will have a reflectance less than 5% over the spectral range 300 nm to 1800 nm and over a wide range of incident angles. The coatings will be completely compatible with inverted metamorphic (IMM) multi-junction solar cell technology and will be optically matched to IMM solar cells. We expect the new coatings will enable a relative efficiency increase of at least 7%, corresponding to a 2.5% absolute efficiency increase.

The ARC technology to be developed in the proposed program will be applicable to the generation of multi-junction solar cells currently in use and to the novel solar cell designs currently under development. It will therefore have application in all current solar-powered NASA space missions and in forthcoming projects such as solar electric propulsion (SEP). The technology will also increase the efficiency of solar cells that are used to extend the duration of electrically powered unmanned aerial vehicles (UAVs). The ARC technology is also applicable to the epitaxial lift-off (ELO) solar cell technology under development by MicroLink. It will therefore be possible to combine the increased efficiency enabled by the new ARC technology with the lightweight, flexible, reduced-cost ELO solar cells.

The ARC technology to be developed in the proposed program will be applicable to the multi-junction, Ge-based solar cells currently in use in commercial and military applications. Similarly, the technology can be used to enhance the efficiency of solar cells for UAV applications and for terrestrial applications. The ARC technology is also applicable to the epitaxial lift-off (ELO) solar cell technology under development by MicroLink. It will therefore be possible to combine the increased efficiency enabled by the new ARC technology with the lightweight, flexible, reduced-cost ELO solar cells.

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