1-8. Advances in Thin-film Solar Cells for Lightweight Space Photovoltaic Power GEOFFREY A. LANDIS, SHEILA G. BAILEY & DENNIS J. FLOOD Summary The present status and current research directions of photovoltaic arrays as primary power systems for space are reviewed. There have recently been great advances in the technology of thin-film solar cells for terrestrial applications. In a thin-film solar cell the thickness of the active element is only a few microns; transfer of this technology to space arrays could result in ultra low-weight solar arrays with potentially large gains in specific power. Recent advances in thin-film solar cells are reviewed, including polycrystalline copper-indium selenide (CuInSe^ and related I-III-VI(2) compounds, poly crystalline cadmium telluride and related II-VI compounds, and amorphous silicon:hydrogen and alloys. The best experimental efficiency on thin-film solar cells to date is 12% AMO for CuInSe2. This efficiency is likely to be increased in the next few years. The radiation tolerance of thin-film materials is far greater than that of single crystal materials. CuInSe2 shows no degradation when exposed to 1-MeV electrons. Experimental evidence also suggests that most or all of the radiation damage on thin-film materials can be removed by a low temperature anneal. The possibility of all thin-film cascade multibandgap solar cells is discussed, including the trade-offs between monolithic and mechanically stacked cells and voltage-matched versus current-matched configurations, and remaining problems to be solved. The best current efficiency for a cascade cell is 12.5% AMO for an amorphous silicon on CuInSe2 multibandgap combination. Higher efficiencies are expected in the future. For several missions, including solar-electric propulsion, a manned Mars mission, and lunar exploration and manufacturing, thin- film photovoltaic arrays may be a mission-enabling technology. 1. Introduction In this paper we discuss the development of photovoltaic arrays beyond the next generation, particularly looking at the potentials of thin-film polycrystalline and amorphous cells. We discuss two important figures of merit, efficiency (i.e. what fraction of the incident solar energy is converted to electricity), and specific power (power to weight ratio). Geoffrey A. Landis, Sheila G. Bailey and Dennis J. Flood, NASA Lewis Research Center, MS 302-1, Cleveland, OH 44142, USA. Paper number IAF-ICOSP89-1-8.
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