Advances in amorphous silicon photovoltaic technology
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Advances in amorphous silicon photovoltaic technology D. E. Carlson, K. Rajan, R. R. Arya, F. Willing, and L. Yang Solarex, a Business Unit of Amoco/Enron Solar, 826 Newtown-Yardley Road, Newtown, Pennsylvania 18940 (Received 2 March 1998; accepted 2 March 1998)
With the advent of new multijunction thin film solar cells, amorphous silicon photovoltaic technology is undergoing a commercial revival with about 30 megawatts of annual capacity coming on-line in the next year. These new a2Si multijunction modules should exhibit stabilized conversion efficiencies on the order of 8%, and efficiencies over 10% may be obtained in the next several years. The improved performance results from the development of amorphous and microcrystalline silicon alloy films with improved optoelectronic properties and from the development of more efficient device structures. Moreover, the manufacturing costs for these multijunction modules using the new large-scale plants should be on the order of $1 per peak watt. These modules may find widespread use in solar farms, photovoltaic roofing, as well as in traditional remote applications.
I. INTRODUCTION
The first amorphous silicon (a2Si) solar cell was made at RCA Laboratories in 1974,1 and the first publication appeared in 1976.2 Only four years later, in 1980, Sanyo introduced the first commercial product utilizing a2Si photovoltaic (PV) technology when they used a small a2Si PV module to provide power for a calculator. Within a period of several years, sales of solar-powered calculators were on the order of 100 million units per year, and a2Si solar cells accounted for about 30% of all PV sales worldwide. In the mid-1980s, many people expected low-cost, large-area a2Si PV modules to usher in a period of explosive growth for terrestrial power applications. However, this promise did not materialize for several reasons. First, the stabilized performance of singlejunction a2Si solar cells was limited to conversion efficiencies of about 5%. (Thus, the total PV systems cost was still relatively high due to area-related, balance of system costs.) Another factor limiting the commercialization of a2Si solar cells for terrestrial power applications was the unproven track record for prolonged use outdoors. Moreover, in order to achieve low manufacturing costs for a thin-film PV technology, one must build a plant with a capacity on the order of about 10 MWyy, and no company was willing to make such a commitment in the mid- and late 1980s due to both uncertainties in the market and the factors mentioned above. In the last few years, the situation has changed with the advent of a2Si multijunction solar cells. Considerable progress has been made over the last two decades in improving the optoelectronic properties of the a2Si alloys, and stabilized conversion efficiencies in the range 2754
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 10, Oct 1998
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of 8 to 10% have been demonstrated recently for largearea a2Si multijun
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