Dirty silicon could pave way for cheaper solar energy

A research team led by engineers at the University of California, Berkeley, has developed a new technique to handle metal defects in low-grade silicon, an advance that could reduce the cost of solar cells.

The research, supported by the U.S. Department of Energy’s National Renewable Energy Laboratory and its University Crystalline Silicon Research Project, could make solar energy more efficient and available. “We have proposed a new approach to the use of dirty silicon,” said Eicke Weber, UC Berkeley professor of materials science and engineering, principal investigator of the Center for Advanced Materials at the Lawrence Berkeley National Laboratory (LBNL), and principal investigator of this research project. “Instead of taking the impurities out, we can leave them in but manipulate them in a way that reduces their detrimental impact on the solar cell efficiency.” The team analyzed how metal contaminants in silicon respond to different types of processing using highly sensitive synchrotron X-Ray microprobes capable of detecting metal clusters as small as 30 nanometers. “We were able to improve the distance electrons could travel by a factor of four compared with dirty silicon that had been left unaltered,” said Tonio Buonassisi, a Ph.D. student in materials science and engineering at UC Berkeley. “Although this is still not as efficient as ultrapure silicon, it is the proof of principle that poor-quality silicon can be easily improved. We are now looking at other techniques that could further enhance the efficiency of dirty silicon.” “Solar energy is often touted as the most promising and secure alternative energy source, capable of reducing our dependence on foreign fuels while reducing the emission of dangerous gases that harm world climate,” said Weber. “The approach we are proposing could lead to substantial progress in making solar energy more widely available with just a few tweaks in the manufacturing process.” The researchers say that by 2006, the photovoltaic industry is projected to use more silicon than the microelectronic industry, and that keeping solar energy cost-effective may depend upon finding ways to utilize the dirtier, cheaper silicon material. “As solar electricity moves into mainstream power generation, the production of high-quality silicon has not kept pace with demand,” said Andrei Istratov, assistant research engineer at UC Berkeley. “The resulting shortage in supplies of high-grade silicon has caused its price to increase by up to 800 percent on the spot market. Since the solar cell wafer comprises more than half of the cost of the solar cell device, this has translated into recent price increases for solar cells. We believe that our engineering concept has the potential to help the photovoltaic industry remain competitive as an alternative energy source.” For the full press release and more information, see the following link.
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