A microscopic assembly line of genetically engineered viruses has helped create more efficient solar cells in an MIT lab. Such viruses help control the arrangement of tiny, hollow carbon nanotubes in a way that boosts the power efficiency of converting sunlight into electricity by almost one third. The improvement adds very little cost to making solar cells, because the viruses add just one simple step to the usual manufacturing process.
"A little biology goes a long way," said Angela Belcher, a materials chemist at Massachusetts Institute of Technology.
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When sunlight knocks electrons loose from solar cell materials such as silicon, the electrons flow into a collector and create a current that charges batteries or powers devices. Nanotubes offer the promise of creating a more direct path for those electrons. But researchers have problems making nanotubes that won't clump up and reduce their own effectiveness.
To solve that problem, the MIT team decided to harness modified M13 viruses – typically known for infecting bacteria.
Each virus can bind five to 10 nanotubes and hold them in place to overcome the clumping problem. The viruses were also engineered to coat the nanotubes with titanium dioxide (TiO₂) – a main ingredient for certain solar cells. The TiO₂ coating helps the nanotubes channel electrons even more efficiently. Researchers can direct viruses to perform either the binding task or coating task by adjusting the acidity of the environment. The viruses even make the nanotubes soluble in water at room temperature, which makes it easier to combine the nanotubes with the solar cells.
The combined weight of the viruses and nanotubes makes up just 0.1 percent of the weight of a finished solar cell.
The work is an "impressive" step up from past efforts to use nanotubes in solar cells, Prashant Kamat, a professor of chemistry and biochemistry at Notre Dame University, said. Kamat added that the solar cell industry could quickly adapt such an improvement if it holds up through additional testing.
