The Department of Materials Science and Engineering welcomes you to its 2015 Winter Colloquium Series.
Location: Tech L361, 4:00pm
Supratik Guha
IBM Research
“Earth abundant vacuum deposited kesterite thin film solar cells”
For solar cells to be cheap and available in quantities to meet demands of ~ 50 GWp/year (for photovoltaics to make a significant dent in worldwide electricity production), it is desirable that they be made of materials that are earth abundant, stable, preferably non-toxic, and viable in polycrystalline form (to obviate the need for expensive single crystal substrates). Among the new materials being investigated, the kesterite compound copper zinc tin sulfide (CZTS) is an attractive solar cell absorber material that meets these criteria, provided the efficiencies of the cells can be increased to beyond its current value of ~9%. If one is willing to add some Se (CZTSSe) and tolerate some non-toxicity, efficiencies of ~ 12-12.5% may be achieved. These numbers however need to be >~15% for for pre-manufacturing activities in CZTS or CZTSSe to begin, and likely >~18% for them to be successful candidates for manufactured products in the future. Using examples from vacuum deposited CZTS, I will describe some of the materials issues that limits current electrical performance, the most significant among them being an open circuit voltage that is quite low. I will describe the role that microstructure and phase stability in this material plays, and the effect that Na addition has on grain growth and photovoltaic properties. In order to identify the role of extended defects and grain boundaries on performance, we have also begun a study of epitaxial CZTS grown on near lattice matched silicon substrates by molecular beam epitaxy, and these results will be discussed. Finally, I will show some of our early results in the successful demonstration of monolithic tandem kesterite-perovskite solar cells.
Biography:
Supratik Guha is presently the Director of Physical Sciences at IBM Research, where he has been since 1995. During his time at IBM he initiated and led the high dielectric constant (high-k) oxide materials research at IBM and was responsible for some of the key materials and processes that led to IBM's high-k metal gate CMOS technology. His current research interests are in new semiconductors and oxides for logic, and energy conversion applications. Supratik received his Ph.D. in Materials Science from the University of Southern California in 1991, and his B. Tech from the Indian Institute of Technology, Kharagpur (India) in 1985. He is also currently an adjunct professor of materials science at Columbia University. He is a fellow of the American Physical Society and the Materials Research Society.
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