Tobacco farmers, faced with fewer traditional buyers for their crops, are looking to the solar industry
for income. Plants such as tobacco are sunlight collectors with many similarities
to solar cells. Now, a group of scientists is trying to take advantage of that collection
system to produce inexpensive and biodegradable solar cells.
In a study reported in the January 2010 issue of Nano Letters,
investigators from the University of California, Berkeley, demonstrated how to program
tobacco plants to enhance their sunlight collection system. They genetically engineered
a virus called the tobacco mosaic virus and sprayed it over the tobacco plants.
This forced the plants to artificially produce lots of chromophores, which form
the basis of the collection system and convert photons from sunlight into electrons.
Scientists from the University of California, Berkeley, demonstrated how to program tobacco
plants to make use of their sunlight collection system.
The trick, the scientists found, is that the chromophores must
be spaced at a fairly precise distance of about 2 or 3 nm from one another. If the
chromophores deviate from this spacing, the electric current is halted, or the electrons
are more difficult to harvest. Fortunately, tobacco plant cells are very good at
lining up chromophores at this exact distance from each other in a long spiral measuring
hundreds of nanometers long. The team was able to exploit this plant structure to
grow strands of chromophores.
The researchers were able to extract the chromophore structures
when they harvested the plants. After dissolving the structures in a liquid solution,
they sprayed the new solution on a glass or plastic substrate to create a solar
cell.
The next step in their work will be to demonstrate that the resulting
solar cells can turn light into electrical energy. They also demonstrated how to
manipulate E. coli bacteria to produce chromophore structures. In this case, instead
of using a virus, they modified the bacteria directly.
Compared with traditional solar cells, those made from plants
or bacteria have several potential pluses. For instance, they don’t require
the use of toxic chemicals, they’re biodegradable, and they’re inexpensive
to produce. The downside is that bio-based solar cells likely have a shorter lifetime
than silicon ones.