6N Silicon – Calisolar – Suntech – Technology Review

Cheaper High-Efficiency Solar Panels – is the title of this article out of Technology Review about two weeks ago.

Silicon wafers for use in solar panels require both the defect density and impurity levels are below low minimum values.  The low defect density is best achieved with single crystal wafers.  These are commonly produced by techniques that include the Czochralski single crystal growth process that is described in the article.  With regard to impurities the feedstock for a given single crystal growth technique has often undergone expensive purification processes, considerably adding to the cost of the final wafer and solar cell.

To reduce the costs associated with the crystal growth portion of wafer fabrication Suntech, as described in the article, is implementing a much simpler casting technique.  As discussed in the article Suntech has advanced upon a now public domain seed casting process.  Suntech’s improvements on this process reduce the amount of crystal nucleation naturally occurring along the crucible walls, a heterogeneous surface.  The result is a increased fraction of the ingot is a single grain allowing the overall ingot to approach a single crystal.  This discussion is certainly supported by the solar panel presented in the article’s figure.  There appear to be smaller grains grouped around the periphery of an individual cell of the panel, likely corresponding to the portion of ingot contacting the crucible.  A larger grain, which approaches a single crystal, lies roughly in the middle.  So far so good.

So what about the impurity level?  Will Suntech be using traditional feedstock for their casting process or will there be cost savings here as well?  This takes us back to Suntech’s October 19, 2010 press release, announcing the extension of their strategic partnership with Calisolar.  The release further discusses Suntech’s support for the addition of capacity to Calisolar’s 6N Silicon facility in Ontario.  6N Silicon was founded around a new technology for the purification of silicon for the solar industry. United States Patent 7,727,503 to Scott Nichol discloses at least aspects of the technology, which side-steps traditional purification techniques through a novel implementation of less expensive extractive metallurgy to at least largely meet the required purity levels.

To close the circle Suntech may be using silicon that has been purified with the techniques now owned by Calisolar for their casting process.  So my guess is that Canadian technology will be part of the cost reduction of the final solar panels.