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Hybrid Solar Cells Combine Nanotech with Plastics

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  • RemyC
    From: http://www.msnbc.msn.com/id/3079001 Solar-cell tech turns to plastic power Researchers developing flexible, cheap devices that use sun s energy (Photo:
    Message 1 of 1 , Jan 1, 2005

      Solar-cell tech turns to plastic power
      Researchers developing flexible, cheap devices that use sun's energy

      (Photo: Janke Dittmer, Wendy Huynh and Paul Alivisatos of the University of
      California at Berkeley show off an experimental array of solar cells. An
      electrical current is generated within a brownish-orangish film of plastic.)


      Lynn Yarris
      lcyarris@ lbl.gov

      Robert Sanders
      rls@ pa.urel.berkeley.edu

      By Alan Boyle
      Science editor

      March 28, 2002 - Researchers are finding new ways to make solar power cells
      out of plastic - creating electricity-generating materials you could print
      on a sheet of paper, stick onto your windows, have painted on your house, or
      even wear on your back. They say plastic power could go commercial in just a
      few years.

      Most people think of solar cells as the large arrays of dark, glassy squares
      that provide electricity for the international space station, the Hubble
      Space Telescope and earthbound solar-power pioneers trying to break their
      reliance on the power grid. But when it comes to 21st-century photovoltaics,
      the trend is heading toward a thinner, cheaper breed of solar cell.

      The state of the art in solar power involves flexible thin-film sheets of
      laminated semiconducting material that can convert 20 percent to 35 percent
      of the sun's energy into electricity. The problem with thin-film cells is
      that they're still relatively expensive to manufacture, requiring clean
      rooms and vacuum chambers.

      Several teams of researchers are trying a completely different approach,
      using plastics spiked with exotic inorganic materials like buckyballs or
      nanorods. Such materials could be mixed up like paint or ink, then sprayed
      or silk-screened onto a surface in combination with flexible electrodes.

      "We use a much dirtier process that makes it cheap," said A. Paul
      Alivisatos, a chemistry professor at the University of California at
      Berkeley and a researcher at Lawrence Berkeley National Laboratory.

      One path of power
      Alivisatos and two colleagues, Wendy Huynh and Janke Dittmer, describe the
      process in Friday's issue of the journal Science. It's not yet ready for
      prime time, since the solar cells achieved efficiencies of only 1.7 percent
      and produced only about 0.7 volts of electricity. But the researchers
      believe they're just beginning to follow a trail that could lead to the next
      generation of portable power.

      The Berkeley team created a blend of organic polymers and an assortment of
      two types of nanorods - clusters of cadmium selenide molecules that looked
      like grains of rice but measured only 7 or 60 nanometers in diameter. The
      nanorods were designed so that they absorbed particular wavelengths of light
      and converted them into electrical current. The key was the shape and
      orientation of the nanorods, Alivisatos said.

      "Because the electron mobilities are higher in the rods, we can make a lot
      of improvement over time," he told MSNBC.com. "Usually, the efficiency will
      end up being related to how good the mobility is in these materials."

      That's what gives Alivisatos hope that the Berkeley breed of solar cells
      will eventually approach the 10 percent efficiency level required for a
      commercially viable product, by using a standard toolbox of engineering

      Eventually, the material, which "looks like a tinted car window that has a
      brownish-orangish tinge to it," could be sprayed onto glass, stuck on a
      briefcase, even plastered onto clothes for wearable electronics, he said.

      "I don't know if the color would look so great" for clothing, he joked. "It
      may be a design feature."

      Inkjet electronics
      Another team at the University of Arizona is using a similar approach to
      plastic solar cells, employing carbon-based buckyballs - exotic molecules
      that look like spherical cages - rather than the Berkeley team's nanorods.

      Each team is familiar with the other's work. Alivisatos said his research
      was following in the Arizona team's footsteps, while Ghassan Jabbour, an
      optical sciences professor at Arizona, told MSNBC.com that Alivisatos' work
      was "excellent ... it's another variation of doing photovoltaics."

      "By no means is one approach better than the other," said Jabbour, whose
      findings have been published in Applied Physics Letters. "The fact that none
      of them has shown more than 5 percent efficiency shows that there is a lot
      of work to be done."

      Nevertheless, Jabbour is optimistic that he's also on the right trail. He
      says his plastic solar cells have achieved efficiencies of more than 2
      percent, and his team recently demonstrated an inkjet-printing system that
      could spray a light-emitting layer onto an electrically conductive surface.
      The experiment produced self-illuminated images, printed on plastic - but
      the same principle could be applied someday to create electronic circuits on
      paper, glass or clothing.

      Such techniques could dramatically lower the cost of solar cells in the next
      five years or so, Jabbour said.

      "You can make them by the mile and sell them by the inch," he said.

      Jabbour said the first applications would involve "short-term,
      light-emitting devices or other types of microelectronics that would only
      require very low power": for example, paper-thin disposable pagers, watches,
      calculators, perhaps even a small, head-mounted computer.

      But he also dreams of the day when curtains and wallpaper could be coated
      with power-generating plastic.

      "I would like to make a window or a curtain so that one side can be
      photovoltaic and the other side is a light-emitter," he said. That way, the
      tinted window could soak in the sunlight during the daytime, then light up
      the room at night, he said.

      "It's pretty exciting stuff we're doing here," Jabbour said.

      © 2004 MSNBC Interactive

      Additional info:

      Berkeley Media:

      One potential product is a new type of solar cell that performs like a
      traditional solar cell, but can be configured like a light weight, flexible
      plastic. In particular, this technology has the potential to provide low
      cost solar power through currently available, high volume and inexpensive
      manufacturing techniques based on conventional film based processes such as
      roll to roll manufacturing. To develop our nanotechnology-enabled solar
      cells we are collaborating with Matsushita and several United States
      government agencies.
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