Less-expensive raw materials in lower quantities could mean fewer production steps in manufacturing solar panels — and potentially lower energy consumption. A team from the Norwegian University of Science and Technology (NTNU) has developed a new processing technique that uses about 1000 times less pure silicon and about two-thirds less energy than traditional solar cell fabrication methods. It is based on an emerging design called vertical rod radial junction. The active part of these solar cells is the silicon core, which has a diameter of about 100 µm. Images courtesy of Fredrik A. Martinsen/NTNU. The NTNU cells are composed of silicon fibers coated in glass. The cells are fabricated from polycrystalline, low-purity p-type silicon material that forms silicon-core/silica-sheath fibers through bulk glass draw techniques, the researchers wrote in a study. Specifically, the silicon core is inserted into a 30-mm-diameter glass tube that is heated to melt the silicon and soften the glass. The tube is stretched until the core measures about 100 µm. Traditional solar cells require pure silicon wafers, which are often expensive and energy-intensive to produce. This new technique has already demonstrated a more efficient manufacturing process, the researchers said. “We can use relatively dirty silicon, and the purification occurs naturally as part of the process of melting and re-solidifying in fiber form,” said Dr. Ursula Gibson, a physics professor at NTNU. “This means that you save energy and several production steps.” The new silicon fibers also tout a shorter distance between where the charge is generated to where it is captured. By using silicon fibers coated in glass, researchers have been able to make solar cells from silicon that is significantly more impure, and thus cheaper, than existing industry standards. “The vertical rod design still isn’t common in commercial use,” said Fredrik Martinsen, a doctoral candidate at NTNU. “Currently, silicon rods are produced using advanced and expensive nanotechniques that are difficult to scale. But we’re using tried-and-true industrial bulk processes, which can make production a lot cheaper.” The next step for the researchers will be to refine production to make larger and more effective solar cells, and couple multiple cells together. The team continues to improve the design and fabrication processes, as well as the prototype cells’ power efficiency, which is currently at 3.6 percent — contemporary solar cells have an efficiency of about 18 percent, according to the researchers. “These are the first solar cells produced this way, using impure silicon. So it isn’t surprising that the power output isn’t very high,” Martinsen said. The research was published in Scientific Reports (doi: 10.1038/srep06283). For more information, visit www.ntnu.edu.