Finding Better Materials for Solar Cells
In recent months, just as falling oil prices and a worldwide economic slowdown have dulled solar’s gleam and made it less attractive as a power source than coal and gas, hundreds of solar technology factories have cropped up around the world. Meanwhile, the cost of silicon has dropped by half. Industry analysts are forecasting that by 2010, as a result of the recent solar industry buildup, the supply of silicon for solar panels will far exceed demand — driving prices down even more.
Hurtling over the silicon cost factor had been a priority for researchers looking to develop other materials that could be used in solar cells — but so was efficiency. Several advancements have been made as a result, though it now remains to be seen how commercially viable they will be. Researchers at Ohio State University, for example, recently announced they had devised a potential solar cell material that can capture the entire visible spectrum of sunlight. The material, an electrically conductive plastic combined with metals, such as molybdenum and titanium, has promising properties — including the ability to generate electrons that remain in an excited energy state for a relatively long time. Meanwhile, a team at MIT is looking closely at cuprous oxide, the reddish mineral used as a pigment and fungicide, for its promising optical properties. The team is using defect engineering methods to improve the mineral’s electrical properties. It is also working with nine other compounds that it identified as potential candidates for making solar cells.
Scientists are also looking to refine silicon production processes. Another MIT team, for example, is trying to develop a refining process to chemically or mechanically remove impurities in silicon-rich quartz ore before the melting process — and in doing so, eliminate steps in the costly purifying process. A similar study, also at MIT, seeks to improve the efficiency of solar cells made using multicrystalline silicon, rather than expensive single-crystal wafers, such as those used for computer chips. Multicrystalline materials contain defects within the grains called dislocations, which tend to soak up a lot of the energy produced. The MIT researchers have found that reheating the material to a controlled temperature after it has initially cooled down in the manufacturing process, a technique known as annealing, reduces the energy-sapping dislocations more than a hundredfold — bringing it to nearly the same crystal quality as the pure, single-crystal form. MIT said that part of this research is already well advanced and that the team is working with manufacturers to bring it to market. Pilot runs are expected within a year, and full-scale production soon thereafter.
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