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Sweet treat inspiring cheaper silicon devices

By Katrice R. Jalbuena

A sweet treat served as the inspiration for chemists at the University of Michigan to develop a technique to hit a sweet spot in the development of future low-cost and low-carbon technologies.

Stephen Maldonado, a professor of chemistry and applied physics, along with graduate students Junsi Gu and Eli Fahrenkrug, have developed a way to make crystalline silicon in the same way people have been making rock candy – a treat made from clumps of large sugar crystals - for ages.

Crystalline silicon is a crucial ingredient of such devices as computers and solar cells, however the material and its manufacture are both expensive and energy intensive.

"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," said Mr. Maldonado.

Rock candy, on the other hand, is formed when sugar is added to heated water. The sugar dissolves then reforms into large crystals.

Mr. Maldonado and his team form their crystalline silicon similarly – but at a higher heat of around 180 degrees Fahrenheit.

Instead of sugar and water, they use a solution of silicon tetrachloride, layered over a liquid metal gallium electrode. Electrons from the metal convert the silicon tetrachloride into raw silicon which is then dissolved into the liquid metal.

When heat is applied to the mixture, dark films of silicon crystals accumulate on the surfaces of the gallium electrodes. So far, Mr. Maldonado reports, the crystals are only around 1/2000th of a millimetre in diameter. They hope to improve the technique and make larger crystals.

If the approach proves viable, the team feels that it would have huge implications for the solar energy industry which uses a lot of crystalline silicon but at a high cost.

“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,” said Mr. Maldonado.

The team will continue to explore variations in the process, including the use of lower melting-point alloys. The university is currently pursuing patent protection for the chemist’s findings and seeking commercialization partners to help bring the technology to market. – EcoSeed Staff

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