Speaker: Dr. Eli Yablonovitch (University of California, Berkeley)

Abstract: The Shockley-Queisser (SQ) limit for a single junction solar cell efficiency is about 33.5% under the standard solar spectrum. Previously, the record had been stuck at 25.1% during 1990-2007. Why then the 8% descrepancy between the theoretical limit 33.5% versus the previously achieved efficiency?

It is common 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.

Now, new efficiency records are being broken. Alta Devices has reached 28.2%. Counter-intuitively, efficient external fluorescence is a necessity for approaching the ultimate limits. A great Solar Cell needs to be a great Light Emitting Diode.

About the Speaker: 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 professor of Applied Physics at Harvard. In 1979, he joined Exxon to do research on photovoltaic solar energy. Then, in 1984, Yablonovitch 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 was the Northrop-Grumman Chair Professor of Electrical Engineering. In 2007 he became Professor of Electrical Engineering and Computer Sciences at UC Berkeley, where he holds the James & Katherine Lau Chair in Engineering.