The development of flexible, thin-film, and high-efficiency III-V solar cells enables the design of new flexible, lightweight solar arrays for space applications. A requirement for these solar panels is the replacement of the rigid coverglasses by a flexible shielding layer. In this work, three candidate materials based on commercially available polyimides and synthesized polysiloxanes for such a shielding layer are compared with respect to their ease of synthesis, transparency. Polysiloxanes based on methyltrimethoxysilane (MTMS) based siloxane (MBS) showed the best reproducibility in synthesis of layers of the required thickness of about 300 mm with sufficient transparency and was therefore selected for further analysis. It was demonstrated that the MBS material could be doped with Ce to increase the radiation hardness. Showing virtually no loss of volatile condensable components in outgassing tests it can be concluded that the properties MBS are found suitable for further space qualification testing. V C 2016 Wiley Periodicals, Inc. J. Appl.Polym. Sci. 2016, 133, 43661.
aThe inability of solar cell materials to convert all incident photon energy into electrical current, provides a fundamental limit to the solar cell efficiency; the so called Shockley-Queisser (SQ) limit. A process termed upconversion provides a pathway to convert otherwise unabsorbed low energy photons passing through the solar cell into higher energy photons, which subsequently can be redirected back to the solar cell. The combination of a semi-transparent InGaP solar cell with lanthanide upconverters, consisting of ytterbium and erbium ions doped in three different host materials (Gd 2 O 2 S, Y 2 O 3 and NaYF 4 ) is investigated.Using sub-band gap light of wavelength range 890 nm to 1045 nm with a total accumulated power density of 2.7 kW m À2 , a distinct photocurrent was measured in the solar cell when the upconverters were applied whereas a zero current was measured without upconverter. Furthermore, a time delay between excitation and emission was observed for all upconverter systems which can be explained by energy transfer upconversion. Also, a quadratic dependence on the illumination intensity was observed for the NaYF 4 and Y 2 O 3 host material upconverters. The Gd 2 O 2 S host material upconverter deviated from the quadratic illumination intensity dependence towards linear behaviour, which can be attributed to saturation effects occurring at higher illumination power densities.
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