Monday, November 10, 2008

Advance In Flexible Thin Plastic Solar Cells

Swiss and Chinese researchers lifted the conversion efficiency of a bendable and thin type of solar cell.

Researchers in China and Switzerland are reporting the highest efficiency ever for a promising new genre of solar cells, which many scientists think offer the best hope for making the sun a mainstay source of energy in the future. The photovoltaic cells, called dye-sensitized solar cells or Grätzel cells, could expand the use of solar energy for homes, businesses, and other practical applications, the scientists say. Their study is scheduled for the November 13 issue of ACS' The Journal of Physical Chemistry C, a weekly publication.

The research, conducted by Peng Wang and colleagues - who include Michael Grätzel, inventor of the first dye-sensitized solar cell - involves photovoltaic cells composed of titanium dioxide and powerful light-harvesting dyes. Grätzel cells are less expensive than standard silicon-based solar cells and can be made into flexible sheets or coatings. Although promising, Grätzel cells until now have had serious drawbacks. They have not been efficient enough at converting light into electricity. And their performance dropped after relatively short exposures to sunlight.
In the new study, researchers describe lab tests of solar cells made with a new type of ruthenium-based dye that helps boost the light-harvesting ability. The new cells showed efficiencies as high as 10 percent, a record for this type of solar cell. The new cells also showed greater stability at high temperatures than previous formulas, retaining more than 90 percent of their initial output after 1,000 hours in full sunlight.

These cells offer two potential advantages: First off, they should be lower cost due to expected ease in manufacturing. Second, both their flexibility and their light weight will allow installation in places which otherwise would not support the presence of solar cells. For example, cars could have them on their roofs without a big weight penalty. Also, side walls and other vertical surfaces could be covered with lightweight solar cells whereas much heavier weight silicon photovoltaics would weigh too much for easy installation. Skyscrapers might some day get covered with Grätzel solar cell sheeting.

While they achieved 10% efficiency they only achieved 9.1% efficiency using materials that can be incorporated into a plastic.

The new dye absorbs light far better than the conventional dye. Because the dye absorbs light so well, it's possible to cut the thickness of the active material in the solar cell in half, which makes it easier for electrons to escape the solar cell and reach an external circuit. That, in turn, increases efficiency, in this case to 9.1 percent.

The researchers also paired the new dye with a nonvolatile solvent-based electrolyte. It's not quite as stable as an ionic liquid, and it can't be used with plastic. But it allowed slightly higher efficiencies--up to 10 percent.

With advances happening that cut costs for such a large variety of solar photovoltaic materials I am optimistic about the future of solar energy. PV electric power will come down in cost so far that it will compete with grid power during the day first in high sunlight areas such as the US southwest and gradually in lower and lower light areas. This will slow and eventually stop and reverse the growth of coal burning for electric power. It will also cut natural gas consumption and save it for more valuable space heating and fertilizer production.

Our biggest future energy problem continues to be for transportation. While the world recession has cut oil demand and oil prices the eventual resumption of economic growth will push oil prices back up again and the peak in world oil production is not many years away. I'm still not clear on whether advances in battery technology will happen soon enough to make the transition away from liquid fuels.By Randall Parker at 2008 November 09