At the University of New South Wales (UNSW) in Australia, solar cell researchers have set a record with a conversion rate of 43 percent, outdoing the previous world record by 0.3 percent. The UNSW team, led by Scientia professor Martin Green, joined two US groups to demonstrate a multicell combination that has set the new benchmark for converting sunlight into electricity by any possible approach. “Because sunlight is made up of many colors of different energy, ranging from the high-energy ultraviolet to the low-energy infrared, a combination of solar cells of different materials can convert sunlight more efficiently than any single cell,” said Green, who is also research director of the UNSW ARC Photovoltaics Centre of Excellence. The team, including Dr. Anita Ho-Baillie, developed a silicon cell optimized to capture light at the red and near-infrared end of the spectrum. That cell was able to convert up to 46 percent of light into electricity. When it was combined with four others, each optimized for different parts of the solar spectrum, 43 percent of the sunlight was converted into electricity. “Our group’s silicon cell was the key contributor to the new result,” Green said. Stuart Wenham, a professor and the director of the ARC Center, said the new record was not directly comparable to the 25 percent efficiency world record for an individual solar cell set by UNSW last year. However, it was an important pointer for the future potential of solar photovoltaic power. “This latest record involves an expensive combination of cells, and the sunlight was focused to produce a much higher intensity than standard sunlight for these measurements. It does show, however, what eventually may be practical,” Wenham said. For more information, visit: www.unsw.edu/au Lower-cost solar cells – printed like newspaper, painted on rooftopsIn related news, solar cells could soon be produced more cheaply using nanoparticle “inks” that allow them to be printed like newspaper or painted onto rooftops or the sides of buildings to absorb electricity-producing sunlight, according to reports from the University of Texas at Austin. At the core of Korgel’s research are the nanoparticle “inks” (as shown here) that are the sunlight-absorbing materials of his solar cells. (Images: Beverly Barrett, UT Engineering Public Affairs)Brian Korgel, a chemical engineer at the university, is hoping to cut costs to one-tenth of their current price by replacing the standard manufacturing process for solar cells – gas-phase deposition in a vacuum chamber, which requires high temperatures and is relatively expensive. “That’s essentially what’s needed to make solar-cell technology and photovoltaics widely adopted,” Korgel said. “The sun provides a nearly unlimited energy resource, but existing solar energy harvesting technologies are prohibitively expensive and cannot compete with fossil fuels.” Chemical engineering professor Brian Korgel tests one of his printed solar cells. For the past two years, Korgel and his team have been working on this low-cost nanomaterials solution to photovoltaics – or solar cell – manufacturing. Korgel is collaborating with professors Al Bard and Paul Barbara, both of the departments of chemistry and biochemistry, and professor Ananth Dodabalapur of the electrical and computer engineering department. They recently showed proof-of-concept in an issue of Journal of the American Chemical Society. A roll-to-roll printing process could be used to print the inks onto stainless steel or a plastic substrate. And the prospect of painting the “inks” onto a rooftop or building is not far-fetched. “You’d have to paint the light-absorbing material and a few other layers as well,” Korgel said. “This is one step in the direction towards paintable solar cells.” Researchers apply the nanoparticle “inks” as a spray on the solar cells. Korgel uses the light-absorbing nanomaterials, which are 10,000 times thinner than a strand of hair, because their microscopic size allows for new physical properties that can enable higher-efficiency devices. In 2002, he co-founded a California company called Innovalight, which is producing inks based on silicon. This time, Korgel and his team are using copper indium gallium selenide or CIGS, which is not only less expensive but also benign in terms of environmental impact. “CIGS has some potential advantages over silicon,” Korgel said. “It’s a direct bandgap semiconductor, which means that you need much less material to make a solar cell, and that’s one of the biggest potential advantages.” His team has developed solar cell prototypes with efficiencies at 1 percent; however, they need to be about 10 percent. “If we get to 10 percent, then there’s real potential for commercialization,” Korgel said. “If it works, I think you could see it being used in three to five years.” He also said that the inks, which are semitransparent, could help realize the prospect of having windows that double as solar cells. Korgel said his work has attracted the interest of industrial partners. Funding for the research comes from the National Science Foundation, the Welch Foundation and the Air Force Research Laboratory. For more information on Korgel’s work, go to: www.utexas.edu