: In traditional solar cells, sunlight is absorbed by the cell (made from silicon or titanium dioxide), freeing electrons, which travel across the cell to an electron collector, or electrode. A problem with solar cells is that many electrons don't find their way to the electrode; carbon nanotubes can be used as bridges between the loosened electrons and the electrode, but nanotubes tend to bunch up, decreasing the efficiency and causing short circuits. Researchers have now created genetically engineered viruses can be used to keep the nanotubes in place, increasing energy conversion by nearly one-third. “A little biology goes a long way,” research group leader Angela Belcher told MIT News, noting that the entire virus-nanotube bridging layer represents only 0.1% of the finished cell's weight. How the Heck:
What's the News
The virus (called M13) holds nanotubes in place with its peptides, a protein building block that binds to the carbon nanotubes. A single virus "can hold five to 10 nanotubes, each of which is held firmly in place by about 300 of the virus's peptide molecules," reports Technology Review.
In addition to keeping the nanotubes from clumping, the viruses are also helpful because they're engineered to produce titanium dioxide, which is helpful for solar cells made of the same material, according to chemistry professor Prashant Kamat, who was not involved in the study: “It is likely that the virus template assembly has enabled the researchers to establish a better contact between the TiO2 nanoparticles and carbon nanotubes. Such close contact with TiO2 nanoparticles is essential to drive away the photo-generated electrons quickly and transport it efficiently to the collecting electrode surface.”
What's the Context:
Although most solar cells are composed of silicon, these researchers used a titanium dioxide solar cell. They say their virus-nanotube technique can be applied to other solar cells, such as organic and quantum-dot solar cells.
Connecting the nanotubes with viruses makes the virus-nanotube layer soluble in water, so and can easily be produced at room temperature using a water-based technique.
These same researchers have gotten viruses to do other creative tasks for them, including building a lithium-ion battery.
Not So Fast: Kamat says that “the industry is likely to adopt such processes," but this is an early-stage study, so don't expect to pick up virus-enhanced solar cells from Home Depot anytime soon. Reference: Xiangnan Dang et al. "Virus-templated self-assembled single-walled carbon nanotubes for highly efficient electron collection in photovoltaic devices." Nature Nanotechnology. doi:10.1038/nnano.2011.50
Image: flickr / Mulad
