Doubling the Efficiency of Dye-Sensitized Solar Cells


Dye sensitized solar cells (also known as Grätzel cells) continue innovation at a scorching pace. We recently covered how Shaik Zakeeruddin and Michael Grätzel used ionic liquids to make these solar cells flexible and significantly less toxic. Today we learn from the University of Washington (UW) that it's possible to double the efficiency of dye sensitized solar cells by using a novel popcorn-ball design.

"We think this can lead to a significant breakthrough in dye-sensitized solar cells," said lead author Guozhong Cao, "We did not expect the was a happy surprise."

Cao, a UW professor of materials science and engineering did not set out to increase the maximum efficiency of dye sensitized solar cells. Instead, his team was investigating the difference in how light is absorbed using different processing and design techniques.

The problem with absorption in dye sensitized solar cells is that you not only want to provide a lot of surface area where light can interact, but you also want the light to have multiple 'attempts' at interacting with one of the dyes. The new solar cell strategy takes advantages of a hierarchical (or fractal if you prefer) design to achieve both goals.

At the smallest scale, Cao and his team developed 15 nanometer diameter 'grains' of the solar cell material. The small grains are then clumped together to form aggregate clusters that are about 300 nanometers across (175 of these clusters lined up are about equal to the width of a human hair). The complex internal structure created within the clusters creates tremendous surface area for light to interact with the dye, about 1000 square feet for each gram of material. Yet, at the same time the larger (300 nanometer) structures scatters more light within the entire solar cell creating more opportunities for interaction with other clusters.

The new design vastly improved the efficiency of the dye sensitized zinc oxide cell Cao was working with for this experiment, from 2.4% to 6.2%. Dye sensitized solar cells today traditionally use Titanium dioxide, and can achieve efficiency conversions around 11%.

"We first wanted to prove the concept in an easier material. Now we are working on transferring this concept to titanium oxide," Cao said.

Cao and team think their new design will also increase the efficiency of titanium dioxide dye sensitized solar cells. If the results are similar to what was achieved in zinc oxide, we may see a 20% efficient dye sensitized solar cell in the near future.

Dye sensitized solar cells are cheaper to produce and easier to manufacture than traditional silicon PV cells. Dye sensitized solar cells also offer low toxicity, creative, flexible, and increasingly efficient designs. The future looks bright for the dye sensitized solar cell to play a significant role in our energy matrix. Photo Credit to University of Washington.

via :: UW News

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