Solar Power Lightens Up with Thin-Film Technology

Prices for high-grade silicon (that can generate electricity from sunlight) shot up in 2004 in response to growing demand, reaching as high as $500 per kilogram (2.2 pounds) this year. Enter thin-film solar cells—devices that use a fine layer of semiconducting material, such as silicon, copper indium gallium selenide or cadmium telluride, to harvest electricity from sunlight at a fraction of the cost.

“The fundamental advantage of thin film comes in the form of the amount of material you need,” says electrical engineer Jeff Britt, chief technology officer of thin-film manufacturer Global Solar Energy in Tucson, Ariz. “These are direct bandgap semiconductors. You can get by with one or two microns and still absorb 98 percent of the sunlight.” (In other words, it takes at least 100 times less thin-film material to absorb the same amount of sunlight as traditional silicon photovoltaic cells.)
Global Solar uses a technology known as copper indium gallium selenide (CIGS) to make its thin-film solar cells. The company has already supplied the U.S. military and outdoor enthusiasts with portable field chargers, largely for communication and other small electronic devices powered by such cells. In March, the company opened a new factory in Tucson, where it plans to produce enough thin-film CIGS solar cells to generate 40 megawatts of electricity next year—enough to power roughly 15,000 average American homes; it hopes to boost the juice to 100 megawatts by 2010 in response to what it predicts will be a growing market.

“We’re focusing on low-cost terrestrial power generation,” Britt says. “It’s intended for large-scale, ground-based arrays.” In other words, the types of solar farms previously dominated by traditional silicon photovoltaics now used to generate electricity from sunshine in states like Arizona and California.

Global Solar is not alone. A host of companies, including HelioVolt, Nanosolar and others, are using CIGS technology in an attempt to cut the cost of producing photovoltaic cells. But there are other challenges. “The first hurdle is cost,” says materials scientist B. J. Stanbery, CEO of HelioVolt in Austin, Tex., which is in the process of opening its first CIGS solar cell factory. “The second is efficiency [how much sunlight can be converted to power] and the third is the reliability, [which means the] lifetime of the device.”

Scientific American