Pieces of a silicon wafer (in gray), used for solar cells or computer chips, can be coated or “passivated” using a vapor deposition process, in which the wires shown here are heated to vaporize polymer materials which then are deposited to coat the surface. Credit: Felice Frankel

New room-temperature process could lead to less expensive solar cells and other electronic devices

February 13, 2013 by David L. Chandler

Silicon, the material of high-tech devices from computer chips to solar cells, requires a surface coating before use in these applications. The coating “passivates” the material, tying up loose atomic bonds to prevent oxidation that would ruin its electrical properties. But this passivation process consumes a lot of heat and energy, making it costly and limiting the kinds of materials that can be added to the devices.

Now a team of MIT researchers has found a way to passivate silicon at room temperature, which could be a significant boon to solar-cell production and other silicon-based technologies.

The research, by graduate student Rong Yang and engineering professors Karen Gleason and Tonio Buonassisi, was recently published online in the journal Advanced Materials.

Typically, silicon surfaces are passivated with a coating of silicon nitride, which requires heating a device to 400 degrees Celsius, explains Gleason, the Alexander and I. Michael Kasser Professor of Chemical Engineering. By contrast, the process Gleason’s team uses decomposes organic vapors over wires heated to 300 C, but the silicon itself never goes above 20 C—room temperature. Heating those wires requires much less power than illuminating an ordinary light bulb, so the energy costs of the process are quite low.

Conventional silicon-nitride passivation “is one of the more expensive parts, and one of the more finicky parts, in the processing” of silicon for solar cells and other uses, says Buonassisi, an associate professor of mechanical engineering, “so replacing part of silicon nitride’s functionality with a simplified, robust organic layer has the potential to be a big win.”

Read more: New room-temperature process could lead to less expensive solar cells and other electronic devices — phys.org.

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