April 26, 2011
Genetically Modified Virus Helps Power Solar Cell
MIT reported on Monday that researchers have a used genetically modified virus to produce structures that improve solar-cell efficiency by about one-third.
MIT researchers said they have found a way to make significant improvements to the power-conversion efficiency of solar cells by using a tiny virus to perform detailed assembly work at the microscopic level.
Sunlight hits a light-harvesting material in a solar cell, which releases electrons that can produce an electric current.
The research of this new study is based on findings that carbon nanotubes can enhance the efficiency of electron collection from a solar cell's surface.
However, previous attempts to use the nanotubes had been thwarted by two problems.
The first problem is that creating carbon nanotubes generates a mix of two types, some of which act as semiconductors and some as metals.
The new research has shown that the effects of these two types tend to be different.
The second problem is that nanotubes clump up together, which reduces their effectiveness.
Graduate students Xiangnan Dang and Hyunjung Yi - working with Angela Belcher, the W. M. Keck Professor of Energy, and several other researchers - found that a genetically engineered version of a virus called M13 can be used to control the arrangement of the nanotubes on a surface, keeping the tubes separate so they cannot short out the circuits.
The system the researchers tested used a type of solar cell called dye-sensitized solar cells, which is a lightweight and inexpensive type where the active layer is composed of titanium dioxide.
The researchers said the same technique could be applied to the types as well.
During the study the team enhanced the power conversion efficiency to 10.6 percent from 8 percent by adding the virus-built structures.
This improvement takes place even though the viruses and the nanotubes make up just 0.1 percent by weight of the finished cell.
"A little biology goes a long way," Angela Belcher said in a press release.
The first step is for the energy of the light to knock electrons loose from the solar-cell material. After this, those electrons need to be funneled toward a collector, from which they can form a current that flows to charge a battery or power a device.
The team has previously used differently engineered versions of the same virus to enhance the performance of batteries and other devices. However, Belcher said that the method used to enhance solar cell performance is different.
The research was funded by the Italian company Eni, through the MIT Energy Initiative's Solar Futures Program.
It was published online this week in the journal Nature Nanotechnology.
Image Caption: In this diagram, 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 (the corkscrew shapes in the center) which attach to the carbon nanotubes (gray cylinders) and hold them in place. A coating of titanium dioxide (yellow spheres) attached to dye molecules (pink spheres) surrounds the bundle. More of the viruses with their coatings are scattered across the background. Image: Matt Klug, Biomolecular Materials Group
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