Assistant professor of mechanical engineering Tonio Buonassisi led the MIT team. (MIT/Patrick Gillooly)
An online tool developed by MIT researchers called “Impurities to Efficiency” - or I2E - allows companies or researchers exploring alternative manufacturing strategies to plug in descriptions of their planned materials and processing steps. After about one minute of simulation, I2E gives an indication of exactly how efficient the resulting solar cell would be in converting sunlight to electricity.

A major factor in determining solar cell efficiency is the size and distribution of iron particles within the silicon - even though the silicon used in solar cells has been purified to the 99.9999 percent level, the tiny remaining amount of iron forms obstacles that can block the flow of electrons. But it’s not just the overall amount that matters; it’s the exact distribution and size of the iron particles, which is hard to predict and measure.

A team led by assistant professor of mechanical engineering Tonio Buonassisi, graduate students David Fenning and Douglas Powell, and collaborators from the Solar Energy Institute at Spain's Technical University of Madrid, found a way to use basic physics and a detailed computer simulation to predict exactly how iron atoms and particles will behave during the wafer-manufacturing process. They then used a highly specialized measurement tool — an X-ray beam from a synchrotron at Argonne National Laboratory — to confirm their simulations by revealing the actual distribution of the particles in the wafers.

“High-temperature processing redistributes the metals,” Buonassisi explains. Using that sophisticated equipment, 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.

Already, Powell says, I2E has been used by “research centers from around the world.”

Watch a video on I2E below.