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Online Simulator Optimizes Solar Cell Materials Efficiency

Tonio Buonassisi (Patrick Gillooly/MIT)

Tonio Buonassisi (Patrick Gillooly/MIT)

An online tool offered by MIT helps companies and researchers determine the tradeoffs in manufacturing strategies for solar cells based on planned materials and processing steps. The simulator, which takes about a minute to run, can provide a preview of the efficiency of resulting solar cells in converting sunlight to electricity, a process previously determined largely by trial and error.

The Web-based program was developed in the lab of mechanical engineering professor Tonio Buonassisi (pictured right), with colleagues from the Solar Energy Institute at Spain’s Technical University of Madrid. The online tool focuses on the size and distribution of iron particles in the silicon, considered a critical factor in solar cell efficiency.

Even in its purest form, silicon in solar cells has residual iron particles that can block the flow of electrons. In addition to the overall amount of iron in the silicon, the exact distribution and size of the iron particles are also important to the solar cell’s efficiency, factors that can be both hard to predict and measure.

The MIT/Madrid team developed the Impurities to Efficiency (I2E) simulator to address this problem by modeling the way iron atoms and particles will behave during the wafer-manufacturing process, in particular, the effect of the high temperature processing on distribution of metals in the silicon. The researchers then subjected the results of their simulator to measurements made by an X-ray beam from a synchrotron at Argonne National Laboratory of actual solar wafers. The Argonne Lab’s device is a specialized measurement device that reveals the actual distribution of the particles in the wafers.

“Using that sophisticated equipment,” says Buonassisi, “the team took measurements of the distribution of iron in the wafer, both initially and again after processing, and compared that with the predictions from their computer simulation.” The results from the Argonne Lab, says MIT, confirmed the findings from the simulations.

The I2E site is available free of charge and its developers say it has so far been used some 2,000 times by research centers and manufacturers. One of those companies, Varian Semiconductor Equipment Associates in Gloucester, Massachusetts (acquired by California-based Applied Materials in November 2011), a manufacturer of solar cell production equipment, enabled the company to make its equipment five times faster than before. The overall efficiency of the resulting cells increased somewhat as well.

The following video tells more about the I2E simulator.


Read more: Solar Wafer Process Developer Earns DoE Loan Guarantee

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