Solar Power Research Looks to Nanotechnology

While the sun is a clean, inexhaustible source of energy, it’s relatively expensive compared to the current tendency towards fossil fuels. As issues of pollution and dependence on finite resources become more pressing, lowering the price of solar-powered generation is a major goal of many scientists and companies in the industry.

Merced, California – December 19, 2003 [] That concept serves as the light at the end of a long research tunnel for David F. Kelley, recently named professor in the School of Natural Sciences at University of California (UC), Merced. He has spent the past seven years working toward that goal, and he’s nowhere near finished yet. “If you really believe that what you’re doing has a real benefit, it is a worthwhile endeavor to pursue,” Professor Kelley said. “We’re in the very infancy. However, if these [new] materials lend themselves to the development of solar cells, there would follow a huge technological development.” Kelley wants to make solar cells less expensive by finding materials to replace silicon, which is the current standard but is costly as both a raw material and due to the steps required to remove impurities. With silicon, a small fraction of a percent of impurities renders the material useless in solar cells. One way to fix the impurity problem, he said, is through nanotechnology: you have to make very small semiconductor particles. In an effort to develop alternative energy sources that could reduce the country’s dependence on coal- and nuclear-fired power, the federal Department of Energy funds Kelley’s research. Currently deep in the process of helping design UC Merced’s physical facilities, developing undergraduate curriculum and a research program for UC Merced’s first students, Kelley will teach physics, chemistry and physical chemistry and will instruct freshmen as well as graduate and upper division students. Kelley’s research uses spectroscopy – the study of how light interacts with matter – to understand what occurs in semiconductor nanoparticles. He embarked on this path after spending 15 years pursuing more conventional physical chemistry research. Once he turned his attention to semiconductors, he saw an area ripe for study. The spectroscopy of different types of semiconductor particles represented a long-term project and a true challenge due to its uncharted nature. “David Kelley brings state-of-the-art research in nanoparticles to UC Merced. His work on semiconductor quantum dots has potential relevance for sensors and electronic devices based on nanoparticles,” said Dean of Natural Sciences Maria Pallavicini. “His unique approaches and creativity in tackling complex problems with experimental solutions will provide outstanding opportunities for UC Merced’s undergraduate and graduate students.” Construction of inexpensive, high-efficiency solar cells using nanoparticles of alternative semiconductors may be years away, but the technology holds tremendous promise. Kelley is currently studying the very fast, initial processes that follows the absorption of light in several types of alternative semiconductors – often know as minority carrier lifetime. Absorption of light produces free electrons in the semiconductors, and he and his research group make measurements to determine the fate of these electrons. The longer the semiconductors are active due to the burst of light, the more energy is created. They use time-resolved ultrafast absorption or emission spectroscopy to determine the dynamics of electron trapping and interfacial electron transfer. These measurements are made on nanoparticles of what are now still unusual materials: gallium selenide and indium selenide. The nanoparticles are very small crystals of these semiconductors, typically a fraction of a millionth of an inch across. His immediate research goals are to understand how surface imperfections on these particles affect how electrons transfer off the particles and enter into the electrical circuit. The presence of surface defects, called “electron traps,” can prevent this from occurring; the role of these defects is one of the most important factors in determining how well the solar cell will work. As a result, the understanding and control of electron traps are crucial issues in potential applications of semiconductor nanoparticles.

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