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Solar Windows: Transparent Solar Cells Become Safer
Originally posted on sciy.org by Ron Anastasia on Wed 04 Oct 2006 06:07 PM PDT
 October 04, 2006 |
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Image: © CHINCH GRYNIEWICZ; ECOSCENE/CORBIS
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Plants are the most efficient converters of sunlight
into usable forms of energy, namely, sugar. And our industrialized
society benefits from their efforts over the past few billion years:
organic products, trapped in the passage of time deep below the earth,
were transformed into the oil, coal and natural gas that largely powers
our modern world. Cutting out the middle men--plants and tectonic
processes--seems like a good solution to providing our energy needs.
But man-made cells used to harvest light--so-called solar photovoltaics
and other technologies--lose more of the sun's energy than they absorb,
and they require tremendous amounts of energy to manufacture. One
alternative, known as dye-sensitized solar cells, offers similar energy
capture and lower cost but had relied on potentially toxic liquid
components, preventing its widespread use. Research presented at the
American Chemical Society meeting in San Francisco on September 12,
however, has shown how such cells can be made from safer liquids and
pointed to possibilities for a more bountiful light harvest.
Chemist Michael Graetzel of the Swiss Federal Institute of
Technology in Lausanne developed these dye-sensitized cells more than a
decade ago. Made from cheap, abundant components, these cells use a
titanium dioxide dye to turn 11 percent of incoming light into
electricity--close to the efficiency of standard solar cells used by
homeowners today as shown in the photo. Even so, these cells did not
find widespread use, primarily because they contained toxic liquids
that easily evaporated if not contained. But Graetzel and his
colleagues recently discovered that by substituting ionic
liquids--liquids made up of charged particles, imidazolium iodide in
this case--they could maintain the efficiency and pose no risk of
evaporation. |
| With such solvent issues out of the way, the
dye-sensitized cell offers several advantages, according to its
creator. "You can look through them," Graetzel notes. "Our cell is not
dependent on the angle of light either. It captures light from all
angles." These properties make the cells ideal for things like windows
or roofs, although they are probably less suitable for large-scale
commercial applications, such as solar farms, because they need more
area to produce the same amount of electricity as more typical
silicon-based solar cells. But additional research presented at the meeting may boost their
efficiency: teams from Tokyo University of Science and Notre Dame both
revealed new types of dyes that could extend the spectrum of light
captured by such cells into the infrared range. The Tokyo team relied
on a dye composed largely of ruthenium to absorb infrared light, though
it overlaps too closely with the titanium dye already involved. The
Notre Dame researchers, on the other hand, used organic
compounds--acetylene and ethylene--to attempt to extend the range of
the cells. With or without such improvements, such cells may start
appearing in various applications in the next few years, according to
Graetzel. But the see-through, reddish cells still have a long way to
go to match the light-harvesting power of the original solar cell:
green plants. --David Biello
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