Tel Aviv, Israel--In recent years, developers have been investigating nanotechnology-based light-harvesting thin-film photovoltaic (PV) solar panels--and promoting efficiency metrics to make the technology marketable. Now, Eran Rabani of Tel Aviv University is providing new evidence to challenge recent "charge" measurements for increasing PV-panel efficiency.
Rabani 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.
A caution on multiexciton generation
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.
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.
In 2004, physicists suggested that more than one electron-hole pair could be created from one photon 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," Rabani says.
The theory that Rabani developed with his 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.
Rabani is now on sabbatical at the University of California, Berkeley as a Miller Visiting Professor.
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