Solar Cells Set New Performance Mark

Researchers have announced a solar energy breakthrough that could lead to its more widespread use with their achievement of the highest efficiency ever for one type of solar cells.

The photovoltaic cells, called dye-sensitized solar cells or Gräztel cells, could expand the use of solar energy for homes, businesses and beyond, the researchers say.

Gräztel cells are cheaper to make than standard silicon-based solar cells, but until now they 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.

The research, conducted by Peng Wang of the Chinese Academy of Sciences and colleagues, including Michael Gräztel of the Swiss Federal Institute of Technology, inventor of this type of cell in 1991, involves photovoltaic cells composed of titanium dioxide and powerful light-harvesting dyes.

The team used a new type of ruthenium-based dye to help boost the solar cells' light-harvesting ability. The new cells showed efficiencies as high as 10 percent, a record for this type of solar cell (efficiency is the ratio of useful energy delivered by a system to the energy initially supplied). Most silicon-based solar cells have efficiencies of around 12 percent. But manufacturing silicon is not cheap. The current cost of electricity from silicon-based solar panels for houses or businesses is 25 cents to 40 cents per kilowatt-hour, roughly triple what most people pay their utility company.

Organic solar cells, another up-and-comer, typically convert only 3 percent of incoming sunlight into electricity.

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. Gräztel cells can also be made into flexible sheets or coatings.

The research will be detailed in the Nov. 13 issue of the Journal of Physical Chemistry C, a publication of the American Chemical Society.

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