The idea of boosting the performance of solar cells by coating them with a textured substrate is commonly used in silicon-based cells. The idea is to traps more light so that it bounces around inside the cell instead of reflecting back out, but for a number of reasons, attempts to use textured substrates in polymer solar cells have failed. Now researchers from Iowa State University and the Ames Laboratory have developed a process of producing a thin and uniform light-absorbing layer on textured substrates that improves the efficiency of polymer solar cells by 20 percent.

Previous attempts to use textured substrates in polymer solar cells have proven problematic because they require extra processing steps or technically challenging coating technologies. Some attempts produced a light-absorbing layer with air gaps, a too-thin layer over the ridges, or a too-thick layer over the valleys. These issues resulted in a loss of charges and short-circuiting at the valleys and ridges, which in turn led to poor solar cell performance.

By getting the substrate texture and the solution-based coating just right, the researchers were able to produce a textured substrate pattern consisting of flat-topped ridges less than a millionth of a meter high. The result is a polymer solar cell that captures more light within those ridges – including light that’s reflected from one ridge to another. The cell is also able to maintain the good electrical transport properties of a thin, uniform light-absorbing layer.

According to Sumit Chaudhary, Iowa State assistant professor of electrical and computer engineering and an associate of the Ames Laboratory, tests indicated that the team’s light-trapping cells increased power conversion efficiency by 20 percent over flat solar cells made from polymers. Tests also indicated that light captured at the red/near infrared band edge increased by 100 percent.

This isn’t the only breakthrough in light-trapping technology for solar cells we’ve seen recently. In September, researchers at Stanford University reported that nanoscale solar cells with a patterned rough-surfaced layer could absorb as much as 10 times more energy from sunlight than predicted by conventional theory.

While there’s no word on when we can expect to see solar cells taking advantage of the Stanford University research, the Iowa State University and Ames Laboratory research could soon be headed to commercially available solar cells. The Iowa State University Research Foundation Inc. has filed a patent for the substrate and coating technology and is working to license it to solar cell manufacturers.

Details of the team’s fabrication technology were recently published online in the journal Advanced Materials.

View gallery - 2 images