A solar battery operation is based on the light getting on the photosensitive surface characterised with a “redundancy” of electrons, the latter start shifting into the next in-depth layer of the battery made of “electron-poor” materials. The electromotive force occurs which leads to the emergence of electric current. In fact the two layers interact as electrodes of a regular battery.
Search for materials fit to make solar batteries is of great interest for researchers. Materials based on one-layer carbon nanotubes are considered promising. However, up until now all attempts to use nanotubes for these purposes were unsuccessful as their ability to conduct electric current is highly dependent on the method of production which influences their structure to a great extent.
The study conducted at the Massachusetts Institute of Technology and published at the Nature Nanotechnology shows that composite materials consisting of carbon nanotubes, viruses and titanium oxides can ensure a significant (by 10.6 per cent!) increase in efficiency of capturing electrons from the solar battery element surface.
It was discovered that genetically modified M13 bacteriophages (bacteria-contaminating viruses) can be used to control the spatial organisation of the nanotube groups conducting electric current.
The technology works as follows: The М13 virus consists of a single nucleic acid chain (DNA) and a protein capsule (a capsid). And in this case, the capsid is the one bearing the importance. It is built of multiple similar proteins coded with viral genes. Such uniform structure of the viral surface can be compared to parquet elements repeating. By modifying the genes of the proteins the researchers managed to give the protein chain monomers the ability to bind nanotubes. Each virus could “hold” from five to 10 nanotubes with every nanotube being captured with 300 viral proteins. The use of the technology allows to prevent the nanotubes from sticking together. It is very important as this sticking together was the main reason for the decrease in their conductivity.
In addition, the researchers managed to “ensure” that the М13 virus helps in the next solar batteries production stage — in creating a titanium dioxide photosensitive layer on the surface of the nanotubes. Changes in the medium acidity make the virus interact with the titanium dioxide so that the TiO2 molecules get in the direct proximity of the nanotubes and can freely shift there the electrons emerging after exposure to solar light.
Another fact very important from the production implementation perspective is that all procedures can be performed in an aqueous medium and at room temperature.
The technology results in an increase in solar power conversion efficiency by 10.6 per cent, with the total weight of viruses and nanotubes being under 0.1 per cent of the battery element mass. The researchers believe that this approach will allow for even better performance in the future.
Source of infoormation:
Xiangnan Dang,, Hyunjung Yi,, Moon-Ho Ham,, Jifa Qi,, Dong Soo Yun,, Rebecca Ladewski,, Michael S. Strano,, Paula T. Hammond & & Angela M. Belcher.. Virus-templated self-assembled single-walled carbon nanotubes for highly efficient electron collection in photovoltaic devices. Nature Nanotechnology. Published online 24 April 2011 doi:10.1038/nnano.2011.50.