Iowa State University and Ames Laboratory researchers have improved the efficiency of polymer solar cells through the use of a new process that increases light absorption.
Lead researchers working on the study include Sumit Chaudhary, Iowa State assistant professor of electrical and computer engineering; Kanwar Singh Nalwa, a graduate student in electrical and computer engineering and student associate of the Ames Laboratory; Kai-Ming Ho, an Iowa State Professor of Physics and Astronomy and an Ames Laboratory faculty scientist, and Joong-Mok Park, an assistant scientist in the Ames Laboratory. Together, these researchers have created a new process that increases the efficiency of solar cells.
To do this, researchers took flexible, lightweight polymers and added a textured substrate pattern that provided a uniform and
thin light-absorbing layer. Also, this textured substrate pattern remains uniformly thin when going up and down the flat-topped ridges, which are less than a millionth of a meter high.
The polymer solar cells were indeed much more efficient with this layer, as they were able to absorb
more sunlight within the ridges. The absorbing layer was also able to maintain its electrical transport properties.
"Our technology efficiently utilizes the light-trapping scheme," said Chaudhary. "And so solar cell efficiency improved by 20 percent."
Previous studies have used textured substrates to increase efficiency, but these attempts didn't work because they required difficult coating technologies or additional processing steps. Also, these previous studies had light-absorbing layers that produced air gaps or were too thick or too thin over the ridges, which can cause short circuiting and a loss of charge in the ridges leading to a less
efficient solar cell.
"This may be an old idea we're using," said Chaudhary, "but it's never before been successfully implemented in polymer solar cells."
Not only does this light-absorbing layer make the solar cells 20 percent more efficient, but after testing the polymer solar cells, Chaudhary and fellow researchers found that the amount of light absorbed at the red/near infrared band edge "increased by 100 percent over flat cells."
