The M13 virus consists of a strand of DNA (the figure-8
coil on the right) attached to a bundle of proteins called
peptides - the virus coat proteins which attach to the carbon
nanotubes and hold them in place. A coating of titanium dioxide
(yellow spheres) attached to dye molecules (pink spheres)
surrounds the bundle. (Image: Matt Klug, Biomolecular Materials
Group)
Last year, researchers from the Massachusetts Institute of
Technology (MIT) announced that they had successfully used
carbon nanotubes for "funneling" and
concentrating electrons in photovoltaic cells – this meant
that smaller solar cells created using the nanotubes could
produce as much or more electricity than larger conventional
cells. Now, the efficiency of these nanotube solar cells is
being boosted further ... with the help of a virus.
One of the reported problems with the nanotubes has been
their tendency to clump together and short each other out. To
address that problem, a team of MIT scientists called upon a
genetically-engineered version of a virus known as M13. When
introduced to the nanotube "forest," the virus' peptides
(polymers made from amino acids) bonded tightly with the
nanotubes, both holding them in place AND apart from one
another. One virus is capable of holding five to ten nanotubes,
allotting about 300 peptide molecules to each tube.
Once the virus had performed that service, the scientists
then changed the acidity of its environment, causing it to
produce titanium dioxide (TiO2) and coat each nanotube with the
substance. As the solar cells being tested were of the
dye-sensitized variety, utilizing TiO2 as their active
layer, this also helped the devices to better covert solar
energy to electricity.
Between the superior alignment and the production of TiO2,
the virus-assisted nanotubes increased the solar cells' power
conversion efficiency by about a third, from 8 percent to 10.6.
While the technology was tested on dye-sensitized solar cells,
the scientists say that it should also improve the performance
of other types of solar cells, such as quantum-dot and organic.
Additionally, the virus makes the nanotubes water-soluble,
which allows for them to be introduced to cells via a
water-based, room temperature process. The scientists believe
that it would be relatively easy to add such a procedure to the
solar cell production process.
The MIT
research is published online this week in the journal Nature
Nanotechnology.
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