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Silicon Info: Si PV - Future Trends


The PV industry is expected to continue to grow at an annual rate of more than 30%.  The well-established technology base and ready availability, proven performance, and salubrity of silicon, coupled with economies of scale in larger factories, will likely allow Si to remain the dominant PV material for the foreseeable future. The demand for off-specification polycrystalline silicon feedstock for PV use is likely to exceed the available supply by a factor of at least 2 within the next 10 years, and this will probably be an impetus for development of alternative feedstock material with adequate but not excessive purity levels.

In ingot growth, the trend for single crystals will be away from the smaller 100- and 125-mm-dia. sizes with more focus on 200-mm diameters.  Despite the potential advantages of FZ material, it is unlikely that its role in PV will increase significantly because of higher costs for the crack-free, long cylindrical feedstock it requires and the difficulty in producing the larger FZ diameters.  In CZ growth, we are likely to see an increased effort to make hot zones more energy efficient, to grow larger diameters, and to achieve continuously melt-replenished long growth runs.  An effort will continue to evaluate tricrystalline growth or other means of strengthening the ingots so as to improve breakage yields for thin wafers.  There will be a continuing effort to achieve more wafers per length of ingot, and to take advantage of potentially higher cell efficiencies afforded by thinner wafers when back surface fields are used in the cell design.  Multicrystalline casting, directional solidification, and electromagnetic casting are commanding an increasing share of the Si PV market (53% of all ingot-based modules sold in 1998 were multicrystalline). This trend is likely to continue because the processes and equipment are simpler and the throughputs are higher (especially for electromagnetic casting) by a factor of 5 to 20.

In the ribbon- and sheet-growth technologies, a challenge for dendritic web growth and edge-supported pulling will be to increase areal throughput via wider ribbons, multiple ribbons, or other approaches.  Even though these methods have the advantage of minimal silicon consumption and elimination of wafering, it is unlikely that they can effectively compete with their current throughput of 1-2 m2/day.  This is because the effective areal throughputs of ingot growth range between 30 and 600 m2/day, and other sheet technologies produce 20 m2/day to >1,000 m2/day.  While capillary die growth of octagons produces about 20 m2/day, experimentation is under way to grow large-diameter, thin-walled circular tubes (as depicted in Silicon Ribbon and Sheet Growth) a meter in diameter and much thinner than current octagonal tubes.  This would increase throughput to more than 75 m2/day.  So far, tubes with 0.5-m diameters have been made, effectively doubling the current octagon areal throughput (Roy et al., 1999).  These tubes have been grown less than 100 mm thick. We will probably see continued progress in horizontally pulled, large-area solid/liquid interface sheets by some variant of the method shown in Silicon Ribbon and Sheet Growth because the throughput potential is enormous and one growth furnace could easily generate material for 35 MWp/year or more of solar cell production.

The future is expected to bring continued exploration of thin-layer Si growth approaches, in search of ones that have significant economic advantages over the best ingot and sheet techniques.  Successful ones will have fast deposition rates, large grain sizes, high efficiencies (at least 14% production efficiency), compatibility with low-cost substrates, and amenability to low-cost cell-fabrication schemes.  It is not likely that production of thin-layer Si PV modules will be a significant fraction of the mainstream PV market for at least 10 years, although they, like the ingot and sheet approaches, would have substantial advantages over many other thin-film PV approaches.  These include the simple chemistry and relative abundance of the Si starting material. 

The Earth's crust contains 27.7% Si, in contrast to 0.00002% Cd, 0.00001% In, 0.000009% Se, and 0.0000002% Te (commonly used thin-film elements).  In addition, crystalline Si benefits from an extremely well-established technology base, compatibility with SiO2 surface passivation, relative salubrity with respect to toxicity, and stability under light exposure.
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Roy, A., Chen, Q.S., Zhang, H., Prasad, V., Mackintosh, B., and Kalejs, J.P. (1999) Presentation at the 11th American Conference on Crystal Growth & Epitaxy, Tucson August 1-6.  To be published in J. Crystal Growth.

 


Siliconsultant, P.O. Box 1453, Evergreen, CO 80437 USA                                   e-mailted_ciszek@siliconsultant.com

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This page was last updated on June 19, 2016