UT Researchers Receive $1.4 Million to Continue Work on Solar Cells March 30, 1998 From: Vicki L. Kroll Three University of Toledo faculty members have been awarded $1,427,751 to continue investigating how thin-film solar cells might work with inexpensive materials to harness the energy of the sun. UT has finalized a three-year contract with the National Renewable Energy Laboratory (NREL) of the U.S. Department of Energy for "High Efficiency Thin-Film Cadmium Telluride and Amorphous Silicon-Based Solar Cells." NREL will contribute $870,000 for the project, and UT will provide $557,751. The study will be led by co-principal investigators Dr. Alvin Compaan and Dr. Xunming Deng of the UT physics and astronomy department. Dr. Randy Bohn, UT professor of physics and astronomy, is a co-investigator on the project. All three are members of the University's Center for Materials Science and Engineering. "The objectives of this contract are to improve the understanding of the basic mechanisms of thin-film solar cells on inexpensive substrates such as glass and stainless steel," Compaan said. The award will provide support for six graduate students, as well as undergraduate student and postdoctoral support. Two distinct types of thin-film solar cells are being studied at UT. One of these is based on amorphous silicon and related materials. The other is based on polycrystalline cadmium telluride and related materials. UT has one of the strongest university research groups in the area of thin-film solar cells, with the capability of fabricating both complete amorphous silicon cells and complete cadmium telluride cells. The group led by Deng has recently become the only university group in the United States to fabricate a triple-junction amorphous silicon thin-film cell. The group led by Compaan is the only group worldwide to be able to fabricate cells above 10 percent efficiency in which radio-frequency sputtering is used to deposit semiconductor films that provide the photovoltaic effect. Radio-frequency sputtering electronically charges atoms of argon, creating a plasma that causes cadmium and tellurium atoms from the source to deposit on the glass. After electrical contacts are applied and this thin film (which is one-fiftieth the thickness of a sheet of paper) is hit by sunlight, it produces electrical energy with no moving parts other than electrons. This process is known as the photovoltaic effect. The UT photovoltaics group has strong research collaborations with Solar Cells Inc. of Toledo and Energy Conversion Devices and United Solar Systems Corp., both of Troy, Mich. In addition, the group collaborates with several photovoltaics industrial groups, including International Solar Electric Technologies of Los Angeles, Evergreen Solar of Massachusetts and Materials Research Group of Wheatridge, Colo. The researchers collaborate with academic scientists at NREL, the Chinese Academy of Sciences, the Polytechnic Institute of Mexico City, the Hahn Meitner Institute in Berlin, Brookhaven National Lab and several U.S. universities. In a recent visit to UT, Ken Zweibel, NREL manager of the Thin-Film Partnership Program, said, "With three leading thin-film photovoltaic companies in the area, the Toledo-Detroit region has become a national center for thin-film photovoltaic manufacturing. The University of Toledo, having two strong programs in thin-film photovoltaic research, is in a unique position to work with the industry and push forward the frontiers of photovoltaic research and manufacturing." Since 1989, the UT photovoltaics group of Compaan and Bohn has received more than $1.9 million in external funding for its research in thin-film photovoltaics. This support has been received mainly from the federal government through NREL. With this support, the UT program has developed into one of the world's leading research efforts in thin-film photovoltaics. Its research program on cadmium telluride and related materials is the only program to use radio-frequency sputtering for the deposition of the two semiconductor films. UT also has the only academic program researching the use of high power lasers for scribing of the thin-film layers to integrate photovoltaic modules monolithically for high voltage output. In fall 1996, Deng joined the UT department of physics and astronomy, further strengthening the UT photovoltaics program. His expertise is in the area of amorphous silicon and related thin-film materials. His contributions are recognized in this newest NREL award, which provides support for this effort equal to that for the cadmium telluride-based work led by Compaan. For more information, call Compaan at (419) 530-4787, Deng at (419) 530-4782, or Zweibel at (303) 384-6441.