Table II. Voc (mV), Jph (mA/cm2) and FF values of various RAD no AR-coated thin cells (<100 //m thick) direct from fabrication (virgin), after a low-temperature annealing (LTA) and after hydrogenation (IMPLH). The results in Table 2 illustrate the effectiveness of the two first treatments applied on RAD cells. The basic phenomena involved in these processes were given considerable attention because of their importance for terrestrial photovoltaics and microelectronics. Their full exploitation can be reasonably envisaged in a near future especially for thin materials where their effectiveness is highest. Among the findings of general interest for silicon space cells, it is worth noting that hydrogen passivation may also result in an improved resistance to particulate radiation [22]. Under the reasonable assumption that all the projected improvements of RAD ribbon material may be applied in a coherent process, the performances of large RAD cells may come close to those of single crystalline cells. Conclusion The commercial future of large-power solar space stations is not established yet. Presently, there exists a wide spectrum of technical solutions to this challenge, none of which has proved its definite superiority. Two extreme approaches may be envisaged. The high-efficiency concentrator array based on III-V compound, multiband-gap cells and the relatively low-efficiency planar array based on thin silicon cells. The former will be stimulated by the rapidly-increasing power demand for space stations and the latter will benefit from the continuous progress of silicon industry, including terrestrial photovoltaics. In the latter approach, silicon ribbon growth techniques offer a unique solution to the fabrication of thin, large-area cells. Among these techniques, the RAD process can already produce sheets 5x5 cm surface area and 50 //m in thickness. The performances of the space cells made on this material may ultimately come close to those of single-crystal based technology. REFERENCES [1] Yoshida, S., Mitsui, K., Oda, T., Kato, M., Yukimoto, Y. & Matsuda, S. (1984) in: Proceedings 17th IEEE PVSC, p. 43. [2] Anspaugh, B.E. & Downing, R.G. ibid, p. 23. [3] E.g., Glaser, P.E. (1986) Environmental implications of the Solar Power Satellite concept, Space Power, 6, 4, pp. 279-285.
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