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July 19, 2007

Cheap solar cells could be printed from inkjet printers

Cheap carbon nanotube solar cells that could be printed from inkjet printers are getting closer

Researchers at New Jersey Institute of Technology (NJIT) have developed an inexpensive solar cell that can be painted or printed on flexible plastic sheets. "The process is simple," said lead researcher and author Somenath Mitra, PhD, professor and acting chair of NJIT's Department of Chemistry and Environmental Sciences. "Someday homeowners will even be able to print sheets of these solar cells with inexpensive home-based inkjet printers. Consumers can then slap the finished product on a wall, roof or billboard to create their own power stations."

Mitra and his research team took the carbon nanotubes and combined them with tiny carbon Buckyballs (known as fullerenes) to form snake-like structures. Buckyballs trap electrons, although they can't make electrons flow. Add sunlight to excite the polymers, and the buckyballs will grab the electrons. Nanotubes, behaving like copper wires, will then be able to make the electrons or current flow.

"Using this unique combination in an organic solar cell recipe can enhance the efficiency of future painted-on solar cells," said Mitra. "Someday, I hope to see this process become an inexpensive energy alternative for households around the world."

"Fullerene single wall carbon nanotube complex for polymer bulk heterojunction photovoltaic cells," published June 21, 2007 in the Journal of Materials Chemistry by the Royal Society of Chemistry,


Other progess is being made to develop higher efficiency (6.5%) organic solar cells

Lee says he expects the process will eventually lead to solar cells having three or more layers, and that three cells in tandem could yield an efficiency of nearly 10 percent. Lee's collaborator Heeger is the cofounder of Konarka Technologies , in Lowell, Mass., a well-funded start-up developing plastic solar cells.



Tandem cells are comprised of two multilayered parts that work together to gather a wider range of the spectrum of solar radiation. (Credit: Alan Heeger / University of California - Santa Barbara)

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 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.


The new tandem cells have 6.5% conversion efficiency They expect to make a cost breakthrough.

"It takes 2 U.S. dollars to generate one watt of electric power if you use silicon solar cells," explained Professor Lee, "Only ten U.S. cents [would be required] to generate 1 watt if you use this tandem polymer solar cell," said Lee. The use of inexpensive plastics is a key to cut down the cost for its fabrication. They expect to reach the market in 3-5 years.

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