Posted: October 6, 2009

New kinds of nanotechnology-based luminescent solar concentrators

(Nanowerk News) For years, University of California, Merced, professor David Kelley's research has focused on finding a less expensive method to harness and use solar energy.
While the sun has been used to power small devices such as calculators or landscape lighting, using solar energy on a large-scale basis is costly.
"The technology is good, but it's expensive," said Kelley. "The idea is to make solar energy more practical."
School of Natural Sciences professor Kelley, along with two other UC Merced colleagues, will attempt to do just that by improving existing technology. He received a three-year $1.3 million grant from the National Science Foundation (NSF) to develop luminescent solar concentrators (LSCs) that use materials other than silicon as semiconductors.
For his research, Kelley will attempt to improve a device called a luminescent solar concentrator. These concentrators work by absorbing sunlight across a wide area then re-emitting it onto a small photovoltaic cell. It's less expensive to use luminescent solar concentrators because they don't have moving parts that must track light as the sun moves across the sky.
"UC Merced is pleased that the National Science Foundation recognizes the potential of professor Kelley's work," said Samuel Traina, vice chancellor for research and dean of graduate studies. "Research in this area will contribute significantly to reducing costs associated with solar power generation that could, in turn, lead to wider applications of the technology."
While the sun is an inexhaustible, renewable energy source, using it to produce electricity is expensive for two reasons. First, photovoltaic cells, which convert sunlight into electricity, are made with silicon, an expensive material to use because of the steps needed to remove impurities. Second, many of those expensive solar cells are needed to collect that energy in order to convert it into electricity.
A problem with existing luminescent solar concentrators - made of solar cells, along with glass or plastic and dye molecules that serve to concentrate the light - is that the dyes are organic and don't hold up over time, Kelley explained. Another challenge is that when sunlight bounces around in the plastic, a lot of it gets reabsorbed into the dye molecules and ends up emitted as heat. That energy never makes it to the solar cell.
Kelley, along with professors Valerie Leppert and Boaz Ilan, will attempt to develop new kinds of luminescent solar concentrators, based on nanotechnology. They will develop semiconductor nanorods to use in solar concentrators, replacing organic dyes. The semiconductor nanorods are cylindrical sections of semiconductors, about 1/1000 the diameter of a human hair.
"Our research will develop the physics to understand how these semiconductors can get rid of the problems of self-absorption," Kelley said. "This has the potential to be a transformative technology in solar energy research."
Leppert, an associate professor in the School of Engineering, will use state-of-the-art equipment such as electron microscopes at UC Merced and at the National Center for Electron Microscopy to examine the synthetic materials' properties and whether they can be optimally used in a solar concentrator.
Using information provided by Kelley and Leppert, School of Natural Sciences assistant professor Ilan, will use mathematic models to theorize how the solar concentrators will perform with the nanorods.
"The hope is that over the three years, we will be able to develop a semiconductor that will do what we want it to do," Kelley said, "or, we'll have a more clear understanding of why we can't."
Professors Kelley and Ilan are both members of the UC Merced Energy Research Institute (UCMERI). UCMERI is a multidisciplinary institute that develops new and improved renewable and sustainable energy generation and storage technologies.
Source: University of California, Merced
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