Debunking Solar Energy Efficiency

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"It's bad news for panel producers, but good news for researchers."

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 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.

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.

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.

Prof. Rabani's theory 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 looking for the next realistic step for developing a technology that works.

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