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Weight reduced III-V triple junction cells for SPACE applications

: Köstler, W.; Bergunde, T.; LaRoche, G.; Meusel, M.; Strobl, G.; Zimmermann, W.; Bett, A.W.; Dimroth, F.; Taylor, S.; Schülke, P.; Geens, W.

Lacoste, H.; Ouwehand, L.:
Proceedings of the 8th European Space Power Conference. CD-ROM : 14 - 19 September 2008, Constance, Germany
Noordwijk: ESA, 2008 (ESA SP 661)
ISSN: 0379-6566
ISBN: 978-92-9221-225-4
European Space Power Conference (ESPC) <8, 2008, Konstanz>
Fraunhofer ISE ()

Solar cells contribute to a satellites weight. The weight of triple junction cells depends mainly on the thickness of the germanium substrate, which is the base for the III-V semiconductor layers. Actually, only a few micrometers of the germanium are needed as a photoactive component, which forms the bottom cell of a triple junction structure. The current standard cell has a germanium substrate of 145 micrometer thickness, which is determined by the use of four inch single crystal germanium wafers of that thickness. Performing epitaxy on significantly thinner wafers as well as the cell manufacturing is a challenge due to their mechanical properties. We succeeded to demonstrate that solar cells based on 80 micrometer thin germanium substrates are feasible and that their electrical data are comparable to state-of the-art standard cells. Such cells are approximately one gram lighter than a standard cell. AZUR SPACE plans to qualify the next generation solar cells with an a verage BOL efficiency of 30% and a substrate thickness of 80 micrometer in 2010. Furthermore, the development of even thinner cells is under investigation. We were able to build first demonstration samples of solar cell assemblies (cell, interconnectors and coverglass) with a germanium substrate thickness of only 20 micrometers and an average efficiency of 28.75 %.