Cadmium chloride is a nasty chemical. If it gets on the skin, it releases cadmium, which has been linked to cancer, lung disease and cardiovascular disease. And yet the expensive, dangerous compound has long been used as a coating for thin-film solar cells because it increases the efficiency of converting sunlight to energy. During manufacturing, chemists have to don protective gear and use fume hoods and other precautions to apply the coating, then carefully dispose of the dissolved cadmium waste.
Physicist Jon Major of the University of Liverpool in England and his team set out to find a replacement. They tested numerous alternative salts, including sodium chloride (table salt) and potassium chloride, and found that magnesium chloride yielded comparable efficiency. “We got cells as good as, if not better than, anything we ever got with cadmium chloride,” Major says.
Magnesium chloride is also nontoxic, abundant and costs about 300 times less than cadmium chloride. It can even be applied with a cheap spray coater purchased on the Web. The team published its research online in June in Nature. (Scientific American is part of Nature Publishing Group.)
The new material applies to those solar cells that are made of cadmium telluride, the second most abundant type of solar cell in the worldwide market. Some experts are skeptical that the swap will yield big cost savings because the largest expense varies between manufacturers. Alessio Bosio, a physicist at the University of Parma in Italy, estimates savings will be “minimal,” at about 15 percent. Still, physicist Julian Perrenoud of Switzerland's Empa, a materials science institute, who was not involved in the study, is optimistic. Using magnesium chloride, he says, “will reduce not only the health risks but also the production costs because the raw material is cheaper and much easier to dispose of.”