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Diatoms boost dye-sensitized solar cell efficiency

Posted: 15 Apr 2009 ?? ?Print Version ?Bookmark and Share

Keywords:solar cell? dye sensitized diatom? solar cell silicon?

Researchers at the Oregon State University (OSU) and Portland State University claim that microscopic algae called diatoms could help triple the electrical output of experimental, dye-sensitized solar cells.

By trapping light inside the nanoscale pores of thin-film solar cells coated with diatoms, the engineers claim that more incident photons are captured to boost electricity generation, thereby greatly increasing efficiency.

"In our system, photons bounce around inside pores formed from diatom shells," said OSU professor Greg Rorrer, "making them three times more efficient."

Dye-sensitized solar cells work by absorbing photons on an inexpensive thin-film composed of dye molecules attached to a titanium oxide layer on a glass or plastic substrate. When the dye molecules absorb a photon, the resultant excitation injects electrons into the titanium, which transports them to the negative electrode.

Dye-sensitized solar cells are favored as a thin-film material because they work in low-light conditions and are fabricated with environmentally benign materials compared to silicon solar cells. However, silicon cells have more than twice the efficiency, as much as 20 percent compared to less than 10 percent for dye-sensitized solar cells.

If diatoms could triple the efficiency of dye-sensitized solar cells, they could potentially offer comparable efficiency at a lower cost, especially in low lighting conditions.

The Oregon engineers fed titanium dioxide to living diatoms so they would build shells from the photovoltaic material instead of silicon dioxide, from which they usually build their shells.

"We have found that diatoms will readily accept titanium dioxide in place of silicon dioxide if that's all we make available to them," said Rorrer.

The engineers have grown diatoms on a substrate. They have also bred them in bulk, then coated a glass surface with the material. In either case, the pattern of intricate nanoscale features both boosted the photovoltaic surface area available and trapped incident light inside the pores.

After removing the organic material from the shells, leaving behind the diatom's nanoscale skeletons composed of titanium dioxide, the researchers mixed the material in a dye. The resulting thin-film solar cells had three times the efficiency, according to Rorrer, than the same thin films without diatom nanoscale patterning.

The technique is still experimental, and is expected to add cost to conventional methods of fabricating dye-sensitized solar cells. But Rorrer claims the increased efficiency could justify the extra cost. One reason is that because photons bounce around inside the pores, they have a much greater probability of energizing the dye molecules, thereby coaxing them to release more electrons.

Next, the engineers plan to measure the efficiency of a tiny solar cell consisting of a single diatom. They also plan to optimize the material, which is still not sufficiently efficient for commercial use.

- R. Colin Johnson
EE Times

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