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A new technique could pave the way for a cheaper cost of polymer solar cells and organic electronic devices, while potentially expanding the applications of these technologies.

Researchers at the Georgia Institute of Technology and three other institutions, have enabled production of efficient single-layer solar cells, which could help move organic photovoltaics into a new generation of wearable devices and enable small-scale distributed power generation.

In an exclusive interview with R&D Magazine, Bernard Kippelen, director of Georgia Tech’s Center for Organic Photonics and Electronics and a professor in the School of Electrical and Computer Engineering, said the new process can be a big money and time saver for the electronics industry.

“Instead of doing this at 900 degrees’ heat, we can do this at room temperature and instead of taking one hour it takes one minute,” Kippelen said.

The technique provides a new way of inducing p-type electrical doping in organic semiconductor films by briefly immersing the films in a solution at room temperature.

To achieve this, the researchers immersed thin films of organic semiconductors and their blends in polyoxometalate (PMA and PTA) solutions in nitromethane for a few minutes.

The diffusion of the dopant molecules into the films during immersion led to efficient p-type electrical doping over a depth of 10 to 20 nanometers from the surface of the film.  

The p-doped regions show increased electrical conductivity and high-work function, with reduced solubility in the processing solvent and improved photo-oxidation stability in the air.

For the first time, single-layer polymer solar cells were demonstrated by combining the new method with spontaneous vertical phase separation of amine-containing polymers that leads to efficient electron collection at the opposing electrode.

While most polymer cells are processed using expensive vacuum equipment, the new method provides a simpler alternative to air-sensitive molybdenum oxide layers. The new doping method provided efficient hole collection when applied to polymer solar cells.

“The sunlight gets absorbed by layers of the semi-conductor,” Kippelen said. “The layers are very thin, so you can make them semi-transparent, which you could attach to windows of buildings.”

According to Kippelen, this process could lead to advancements in many device platforms including organic printed electronics, sensors, photodetectors and light-emitting diodes.

Canek Fuentes-Hernandez, a senior research scientist in Kippelen’s research group, explained that the new technique will have a large impact on the industry in the future.

“The realization of single-layer photovoltaics with our approach enables both electrodes in the device to be made out of low-cost conductive materials,” Fuentes-Hernandez said in a statement. “This offers a dramatic simplification of a device geometry and it improves the photo-oxidation stability of the donor polymer.

“Although lifetime and cost analysis studies are needed to assess the full impact of these innovations, they are certainly very exciting developments on the road to transform organic photovoltaics into a commercial technology.”

Felipe Larrain, a Ph.D. student in Kippelen’s lab, said by simplifying the production of organic solar cells areas that lack capital-intensive manufacturing capabilities like Africa and Latin America could allow fabrication of solar cells.

“Our goal is to further simplify the fabrication of organic solar cells to the point at which every material required to fabricate them may be included in a single kit that is offered to the public,” Larrain said in a statement. “The solar cell product may be different if you are able to provide people with a solution that would allow them to make their own solar cells.

“It could one day enable people to power themselves and be independent of the grid.”

Sponsored by the Office of Naval Research, the work was reported Nature Materials. The research also involved scientists from the University of California at Santa Barbara, Kyushu University in Japan and the Eindhoven University of Technology in The Netherlands.

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