According to a UCSB Press Release, higher-efficiency organic solar cells have been made at the university’s Center for Polymers and Organic Solids:
Nobel laureate Alan Heeger, professor of physics at UC Santa Barbara, worked with Kwanghee Lee of Korea and a team of other scientists to create a new “tandem” organic solar cell with increased efficiency. The discovery, explained in the July 13 issue of the journal Science, marks a step forward in materials science.Tandem cells are comprised of two multilayered parts that work together to gather a wider range of the spectrum of solar radiation — at both shorter and longer wavelengths. “The result is six and a half percent efficiency,” said Heeger. “This is the highest level achieved for solar cells made from organic materials. I am confident that we can make additional improvements that will yield efficiencies sufficiently high for commercial products.” He expects this technology to be on the market in about three years.
Heeger and Lee have collaborated for many years on developing solar cells. The new tandem architecture that they discovered both improves light harvesting and promises to be less expensive to produce. In their paper, the authors explain that the cells “… can be fabricated to extend over large areas by means of low-cost printing and coating technologies that can simultaneously pattern the active materials on lightweight flexible substrates.”
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The cells are separated and connected by the material TiOx, a transparent titanium oxide. This is the key to the multilayer system that allows for the higher-level efficiencies. TiOx transports electrons and is a collecting layer for the first cell. In addition, it acts as a stable foundation that allows the fabrication of the second cell, thus completing the tandem cell architecture.