New process improves solar cell efficiency by 20%

A new process that improves the efficiency of polymer solar cells by 20 per cent by increasing light absorption is the latest feat in solar technology, achieved by researchers from Iowa State University and the Ames Laboratory.

"Our technology efficiently utilizes the light trapping scheme. And so solar cell efficiency improved by 20 percent," said Sumit Chaudhary.

According to him, the key was to find a textured substrate pattern that allowed deposition of a light-absorbing layer that's uniformly thin -- even as it goes up and down flat-topped ridges that are 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, he said.

The cell is also able to maintain the good electrical transport properties of a thin, uniform light-absorbing layer.

Tests also indicated that light captured at the red/near infrared band edge increased by 100 per cent over flat cells.

The technology is commonly used in traditional, silicon-based solar cells but previous attempts to use textured substrates in polymer solar cells have failed because they require extra processing steps or technically challenging coating technologies.

Some attempts produced a light-absorbing layer with air gaps or a too-thin layer over the ridges or a too-thick layer over the valleys -- resulting in poor solar cell performance.

But, get the substrate texture and the solution-based coating just right, 'and we're getting more power out," said Kanwar Singh Nalwa, a graduate student in electrical and computer engineering and a student associate of the Ames Laboratory.

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

Details of the fabrication technology were recently published online by the journal Advanced Materials.