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2005 R&D 100 Award Winner

Sinton QSSPC Silicon Evaluation System

Principal Developers: David Mooney and Katie Brown of National Renewable Energy Laboratory; Ron Sinton, Tanaya Mankad of Sinton Consulting, Inc.; Peter Jackson of Jaxon Technical Services, LLC; Stuart Bowden of Institute of Energy Conversion, University of Delaware.

The solar-electric cell and module industry is growing. Given the already tight supply of solar-grade silicon — the semiconductor used in more than 90% of PV devices — the question is: Will we have enough silicon to keep pace with demand and continue pushing PV prices downward? A significant means of keeping up with demand while keeping prices low may be through improvements in the manufacturing process.

The Sinton QSSPC Silicon Evaluation System helps manufacturers detect impurities and defects in silicon material early in the solar cell production process. Low-quality material can be cut from silicon boules and either discarded or re-melted to improve quality — thus saving manufacturers processing time, money, and silicon feedstock. The result is a higher yield of efficient cells and reduced manufacturing costs.

The evaluation system works like this: Before silicon boules are sliced into wafers to be used in silicon solar cell manufacturing lines, a boule tester sends short pulses of infrared light into the boule and measures minority-carrier lifetime in p- or n-type silicon. Using radio frequency (RF) sensing, the tester determines quasi-steady-state photoconductance (QSSPC), then uses this information to calculate the bulk minority-carrier lifetime. Next, it calibrates the results of the photoconductance analysis to determine the absolute lifetime and then determines grain structure and calculates levels of unwanted impurities.

This system will enable the solar industry to keep up with product demand and growth and to produce consistently better silicon at the lowest possible price.