Dec 3, 2010 13:45 GMT  ·  By
Sumit Chaudhary, left, and Kanwar Singh Nalwa of Iowa State University and the U.S. Department of Energy's Ames Laboratory have been working to improve the efficiency of polymer solar cells.
   Sumit Chaudhary, left, and Kanwar Singh Nalwa of Iowa State University and the U.S. Department of Energy's Ames Laboratory have been working to improve the efficiency of polymer solar cells.

Iowa State University along with Ames Laboratory researchers, have successfully developed a process that produces a thin and uniform light-absorbing layer on textured surfaces, thus improving the performances of polymer solar cells in light absorption.

Sumit Chaudhary, an Iowa State assistant professor of electrical and computer engineering and an associate of the US. Department of Energy's Ames Laboratory, said that this “technology efficiently utilizes the light trapping scheme, and so solar cell efficiency improved by 20 percent.”

He added that the idea of a textured surface in order to improve polymer cells' performance is actually an old one, as it is commonly used in traditional, silicon-based solar cells.

However, there is something about it than makes the discovery extraordinary, and that is the difficulty of obtaining an uniformly thin layer.

Previous attempts of using textured substrates in polymer solar cells have failed because they needed either extra processing steps, or technically challenging coating technologies.

Sometimes, the layer had air gaps in it, or it was too thin over the ridges and too thick over the valleys, which led to a loss of charges and a short circuit at the valleys and ridges, in other words, poor solar cell performance.

But once the substrate texture and the coating were right, the researchers managed to obtain more power out of the solar cells.

As Chaudhary explains it, the secret to the performance boost was making the solar cells out of flexible, lightweight and easy-to-manufacture polymers, with the perfect textured substrate pattern, in order to allow the deposition of a light-absorbing, uniformly thin layer.

At the end, the polymer solar cell will capture light within the ridges but also the light reflected by from one ridge to another.

The tests of these textured polymer solar cells showed that they increased power conversion efficiency by 20% over flat solar cells made from polymers, and that the amount of light captured at the red/near infrared band edge was 100% higher than for flat cells.

Chaudhary said that “this may be an old idea we're using, but it's never before been successfully implemented in polymer solar cells.”

This research was supported by the Iowa Power Fund, the Ames Laboratory and the Department of Energy's Office of Basic Energy Sciences, and the details of the fabrication technology were published online by the journal Advanced Materials.