Obviously, much larger cell areas are needed for inclusion in practical spacecraft arrays. In this regard, the Nippon Mining Corporation in Toda, Japan, has produced InP cells with areas of 2 cm2 and 4 cm2, respectively [19, 20]. These latter cells were processed by closed tube diffusion [12, 19, 20] on a production basis. They are intended to power a small lunar orbiting satellite, carried piggyback on board the Japanese MUSES A satellite [21]. The satellite is scheduled for launch in 1990 [21]. The spacecraft, on which the small InP powered satellite is mounted, will perform periodic lunar swingbys. At the first swingby, the small piggyback lunar orbiter will be injected into a lunar orbit. Power for the lunar orbiter will come from 1000 InP solar cells with areas of 2 cm2. Because the moon has no magnetic field, the InP cells will not be subjected to a severe ambient radiation environment. In fact, radiation from solar flares would appear to be the major predictable cause of cell degradation. Hence, rather than serving as a severe test of InP in a space radiation environment, the mission will serve mainly to space qualify the cells. It should be mentioned that, in a production run of approximately 1300 cells, more than 1000 had efficiencies over 15%, the highest efficiency being 16.6% [20]. However, past experience could lead one to predict that higher production efficiencies would be attained using the MOCVD process [11]. The preceding cells are monolithic n on p homojunctions processed by techniques which require operating temperatures of between 600 and 700°C. On the other hand ITO/InP cells are processed at room temperature [22]. These latter cells consist of a layer of w-type indium tin oxide sputtered onto a /’-type InP substrate. Cells of this type have achieved AMO efficiencies of 17%, with no visible barrier toward achievement of higher efficiencies [23], Since we were unable to find any published data concerning their behavior under irradiation, we have irradiated several ITO/InP cells
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