Nanotube-based solar cells harness viruses
Dye sensitized solar cells are a photo-electro-chemical system that positions a semiconductor between a photo-sensitized anode and an electrolyte. Titanium dioxide nanoparticles covered with a dye absorb sunlight, releasing electrons into the anode. These electrons are then collected to power a load, then returned by the cathode to the electrolyte—and the cycle continues. By harnessing a virus to lace the anode with nanotubes, efficiency was boosted from under eight- to over 10.6-percent, according to the MIT researchers.
The MIT research team was led by professor Angela Belcher and her doctoral candidates, Xiangnan Dang and Hyunjung Yi, along with professors Paula Hammond and Michael Strano. Belcher had previously demonstrated that the virus called M13 could fuel the hydrogen economy and pattern thin-film batteries. But their current results for the first time use viruses to keep embedded nanotubes in solar cells separate, so they do not clump or short-out the circuit. Each virus can hold about 10 nanotubes in place with 300 or so peptide molecules, after which the genetically engineered viruses secrete a coating of titanium dioxide.
If the technique proves successful outside the lab, then nanotube-enhanced solar cells will join a vast array of microbial-based products with a global market value of $156 billion in 2011, that is expected to grow to more than $259 billion by 2016, according to BCC Research (Wellesley, Mass.). Microbial-based products include everything from natural yeast for brewing beer to genetically engineered microbes, like the M13 used by MIT, for the commercial production of insulin, biodiesel, and metallurgical products.
The M13 virus consists of a strand of DNA (coil at right) attached to a bundle of proteins called peptides (purple) which attach to the carbon nanotubes (gray) and hold them in place. A coating of titanium dioxide (yellow) attaches to dye molecules (red) which surrounds the bundle. Credit: Matt Klug, Biomolecular Materials Group, MIT.
According to Belcher, MIT’s new technique adds one simple step to the dye-sensitized solar-cell manufacturing process, and can also be adapted to other types of organic and quantum-dot based solar cells.
Funding was provided by the Italian company Eni, through the MIT Energy Initiative’s Solar Futures Program.