27-Oct-2014 - Norwegian University of Science and Technology (NTNU)

Producing solar power with impure silicon

Researchers have developed a technique that allows the use of less pure silicon in solar cells

By using silicon fibers coated in glass, researchers have been able to make solar cells from silicon that is 1000 times more impure, and thus cheaper, than the current industry.

"We're using less expensive raw materials in smaller amounts, we have fewer production steps, and have potentially lower total energy consumption," PhD candidate Fredrik Martinsen and Professor Ursula Gibson of the Department of Physics at NTNU explain.

The researchers' solar cells are composed of silicon fibers coated in glass. A silicon core is inserted into a glass tube about 30 mm in diameter. This is then heated up so that the silicon melts and the glass softens. The tube is stretched out into a thin glass fiber filled with silicon. The process of heating and stretching makes the fiber up to 100 times thinner. This is the widely accepted industrial method used to produce fiber optic cables.

But researchers at the Department of Physics at NTNU, working with collaborators at Clemson University in the USA, are the first to use silicon-core fibers made this way in solar cells. The active part of these solar cells is the silicon core, which has a diameter of about 100 micrometres.

This production method also enabled them to solve another problem: traditional solar cells require very pure silicon. The process of manufacturing pure silicon wafers is laborious, energy intensive and expensive.

"We can use relatively dirty silicon, and the purification occurs naturally as part of the process of melting and re-solidifying in fiber form", says Gibson. "This means that you save energy, and several production steps."

This method is estimated to take roughly one-third of the energy needed to produce solar cells compared to the traditional approach of producing silicon wafers.

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