Joint Colloquium Distinguished Lecture Series
The Opto-Electronics Which Broke the Efficiency Record in Solar Cells
Wednesday, September 7, 2011
The Shockley-Queisser (SQ) limit for a single junction solar cell efficiency is ~33.5% under the standard solar spectrum. Previously, the record had been stuck at 25.1%, during 1990-2007. Why then the 8% discrepancy between the theoretical limit 33.5% versus the previously achieved efficiency?
It is usual to blame material quality. But in the case of GaAs double heterostructures, the material is almost ideal with an internal fluorescence yield of >99%. This deepens the puzzle as to why the full theoretical SQ efficiency is not achieved?
Counter-intuitively, efficient external fluorescence is a necessity for approaching the ultimate limits. Now new efficiency records are being broken. Alta Devices has reached 28.2%. A great Solar Cell also needs to be a great Light Emitting Diode.
Eli Yablonovitch is the Director of the NSF Center for Energy Efficient Electronics Science (E3S), a multi-University Center based at Berkeley. He received his Ph.d. degree in Applied Physics from Harvard University in 1972. He worked for two years at Bell Telephone Laboratories, and then became a professor of Applied Physics at Harvard. In 1979 he joined Exxon to do research on photovoltaic solar energy. Then in 1984, he joined Bell Communications Research, where he was a Distinguished Member of Staff, and also Director of Solid-State Physics Research. In 1992 he joined the University of California, Los Angeles, where he was the Northrop-Grumman Chair Professor of Electrical Engineering. Then in 2007 he became Professor of Electrical Engineering and Computer Sciences at UC Berkeley, where he holds the James & Katherine Lau Chair in Engineering.
Prof. Yablonovitch is a Fellow of the IEEE, the Optical Society of America and the American Physical Society. He is a Life Member of Eta Kappa Nu, and a Member of the National Academy of Engineering and the National Academy of Sciences. He has been awarded the Adolf Lomb Medal, the W. Streifer Scientific Achievement Award, the R.W. Wood Prize, the Julius Springer Prize, and the Mountbatten Medal. He also has an honorary Ph.d. from the Royal Institute of Technology, Stockholm Sweden.
In his photovoltaic research, Yablonovitch introduced the 4n2 light-trapping factor that is used commercially in almost all high performance solar cells.
Yablonovitch introduced the idea that strained semiconductor lasers could have superior performance due to reduced valence band (hole) effective mass. Today, almost all semiconductor lasers use this concept, including telecommunications lasers, DVD players, and laser pointers.
Yablonovitch is regarded as one of the Fathers of the Photonic BandGap concept, and coined the term "Photonic Crystal".
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