Optical Filters on Thin Cover Glass

ABSTRACT: Optical filters on solar cells can improve cell performance by maximizing light transmission into the cell and by helping maintain cell operating temperature with minimal added weight. Anti-reflection films reduce Fresnel reflection losses and maximize light transmitted to the cell. Reflection of below band-gap photons reduces the heat load on the photocell. Reflection of specific in-band spectra also allows for better maintenance of cell temperature and charge density within the cell under certain operating conditions. While anti-reflection coatings and structure surfaces are available for visible commercial applications, the development of high efficiency, multiple band-gap solar cells require coatings to operate over a broad spectral band. Reflection of below band-gap photons which would otherwise be absorbed by the cell as heat is needed to achieve high conversion efficiency. A tandem filter design, using interference and plasma filter layers, is proposed. The plasma layer provides long wavelength reflection while the interference filter provides good in band performance and rejection of specific bands. The below band-gap region beginning at 2.5 microns and extending to long wavelengths is a significant percent of the total spectrum. Since below bandgap photons are absorbed by the cell as heat, radiators are needed behind the solar cell panel to maintain the cells at their optimum operating temperature. BENEFIT: Satellite solar power solutions have both military and commercial applications. This includes space exploration, defense, intelligence, and global communications industries. The coatings could be used on panels from military satellites to communication satellites for cell phones. Further development in optical filters for solar cells would contribute to an increase in the desire for more efficient satellites and therefore create a market pull for the product. Optical filter development to improve the efficiency of solar cell components, for both military and commercial use, is a rapidly expanding market. In addition to improved efficiency, the filters can protect the cells from harmful radiation.