Researchers at the University of Michigan have discovered a novel method of producing crystalline silicon, a material that's not only in high demand in the tech and solar industries, but that also typically comes at a high cost. The raw material, silicon dioxide, or sand, is abundant, but it's no easy task to transform it into a crystalline form of silicon.
"The crystalline silicon in modern electronics is currently made through a series of energy-intensive chemical reactions with temperatures in excess of 2,000 degrees Fahrenheit that produces a lot of carbon dioxide." - Stephen Maldonado, U-M professor of chemistry and applied physics
In contrast, Maldonado and a pair of grad students have developed a process for making silicon crystals at just 180 F, using a method they likened to making 'rock candy' from sugar. While rock candy uses water that is super-saturated with sugar, the new silicon crystal process uses liquid metal instead of water, and silicon instead of sugar.
The team uses a solution containing silicon tetrachloride and layers it over an electrode made from liquid gallium. Electrons from the gallium then convert the silicon tetrachloride into raw silicon, which then get dissolved into the liquid metal.
"The liquid metal is the key aspect of our process. Many solid metals can also deliver electrons that transform silicon tetrachloride into disordered silicon, but only metals like gallium can additionally serve as liquids for silicon crystallization without additional heat." - Maldonado
While the silicon crystals that the process currently produces are only about 1/2000th of a mm in diameter, the team is working to improve the process to be able to make larger crystals, which could then be used in applications such as photovoltaic cells.
"It's too premature to estimate precisely how much the process could lower the price of silicon, but the potential for a scalable, dramatically less expensive and more environmentally benign process is there. The dream ultimately is to go from sand to crystalline silicon in one step. There's no fundamental law that says this can't be done." - Maldonado
The researcher's study is published in the Journal of the American Chemical Society: Direct Electrodeposition of Crystalline Silicon at Low Temperatures