Debunking solar energy efficiency measurements
Public release date: 10-Jan-2011
Contact: George Hunka
ghunka@aftau.org
212-742-9070
American Friends of
Tel Aviv University
Tel Aviv University 'recalculates' efficiency paradigm for
thin film solar panels
In recent years, developers have been investigating light-harvesting
thin film solar panels made from nanotechnology –– and promoting
efficiency metrics to make the technology marketable. Now a Tel Aviv
University researcher is providing new evidence to challenge recent
"charge" measurements for increasing solar panel efficiency.
Offering a less expensive, smaller solution than traditional panels,
Prof. Eran Rabani of Tel Aviv University's School of Chemistry at
the Raymond and Beverly Sackler Faculty of Exact Sciences puts a lid
on some current hype that promises to increase efficiencies in thin
film panels. His research, published recently in the journals Nano
Letters and Chemical Physics Letters, may bring the development of
new solar energy technologies more down to earth.
Prof. Rabani combines a new theoretical approach with computer
simulations. "Our theory shows that current predictions to increase
efficiencies won't work. The increase in efficiencies cannot be
achieved yet through Multiexciton Generation, a process by which
several charge carriers (electrons and holes) are generated from one
photon," he says.
Inefficient as "charged"
But both new and existing theories bode well for the development of
other strategies in future solar energy technology, he points out.
Newer approaches published in journals such as Science may provide
means for increasing the efficiencies of solar technology, and
perhaps would also be useful in storage of solar energy, Prof.
Rabani and his team of researchers believe.
A chemical physicist, Prof. Rabani investigates how to separate
charges from the sun efficiently. In 2004, physicists suggested that
more than one electron-hole pair could be pulled from one photon in
a complicated process in semiconductor nanocrystals. If this were
possible, the charge would be doubled, and so the solar energy
efficiency would increase. "We've shown that this idea doesn't
work," Prof. Rabani says.
One step closer to marketing the sun
The development of more efficient and less expensive devices to make
use of solar energy is one of the greatest challenges in science
today. Billions of dollars are being spent to find the best methods
to collect electron "charges" from the sun.
Typically, one photon from the sun absorbed in a thin film solar
panel can excite one electron-hole pair, which is then converted to
electricity. Currently there are claims that if more electron-hole
pairs can be excited after the photon is absorbed, a larger fraction
of the photon energy can successfully be converted into electricity,
thus increasing device efficiency.
The theory that Prof. Rabani developed with his Israeli colleagues
shows why this process is not as efficient as originally conceived.
It's bad news for panel producers looking to create more efficient
solar panels, but good news for researchers who are now free to look
to the next realistic step for developing a technology that works.
Prof. Rabani is now on sabbatical at the University of California,
Berkeley as a Miller Visiting Professor.
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