Viruses can boost solar cell efficiency

MIT researchers have come up with a rather ingenious, if unusual method to boost the efficiency of dye sensitised solar cells.

The team at the Massachusetts university found that a bacteria-infecting virus known as M13 is extremely useful in holding together carbon nanotubes in a way that enables them to be successfully used in the circuitry involved in manufacturing solar cell technology.

Attempting to use carbon nanotubes is not something that is necessarily new for those looking into how to improve solar cell efficiency, but so far attempts have come a cropper due to a couple of factors, according to the reaserch team.

One of the main concerns for implementing carbon nanotubes is that they often form as either a semiconducting material, which is ideal for solar cell purposes, or alternatively as metals, which can reduces effectiveness.

And when both varieties of nanotubes are produced they tend to group together making it very tricky to make proper circuits with the two types coming into contact, potentially shorting the circuit.

This means that to use nanotubes in conjunction with titanium oxide, the active layer in dye-sensitised cells and a lightweight alternative to traditional silicon based cells, can therefore be difficult.

But virus professor Angela Belcher and her team were able to successfully incorporate the nanotubes with the TiO2 in a way that lead to a significant improvement in the efficiency of the transfer of light into electricity.

According to the researchers, the technique has meant that the power conversion efficiency has jumped from 8 percent to 10.6 percent, a significant improvement due to the addition of the virus.

This efficiency hike is despite a presence of the bacteria at just 0.1 percent the cell weight, with Belcher stating that “a little biology goes a long way”.

The virus works by binding the carbon nanotubes with its proteins known as peptides, which are effective in keeping them separate, with each virus able to hold five to 10 nanotubes in place with around 300 peptide molecules.

Also, the virus is cleverly engineered with a titanium oxide coating which keeps the material in close proximity to the nanotubes – which carry the electrons generated from the coating material.

Essentially the nanotubes help the electrons that are pushed from the titanium oxide towards a collector, providing a “more direct path to the current collector”.

Belcher told TechEye that the work is inspired by a history of research into the use of biological matter in conjunction with other materials, for example, in the production of batteries.

“Biology in this sense is very useful in grabbing things and putting them together at a molecular level, and this novel method has given a good increase in the efficiency of the solar cell,” she said.

While dye sensitised solar cells are currently short of the efficiency seen in traditional devices, there is an increasing uptake, with firms such as Samsung beginning production of the cell type, and the technology already being commercialised in Korea and Japan.

One of the problems with the material, which offers cheaper production costs and a greater range of colour and transparency over traditional methods, has been that that efficiency has not met the relatively high levels already seen with silicon photovoltaic systems.

If the steps taken by the MIT team are able to be scaled up successfully then it could help increase this cheaper form of solar cell.

Belcher notes, however, that the scaling up of the lab work is not something that is at all trivial, but is hopeful that due to the use of such small amounts of biological material the technique is likely to be compatible with existing production methods.

She also points out to us that the project is at a prototype stage, telling TechEye that the next step will be to make a full scale solar cell with her team over the coming year.

Belcher also says that the team is looking at the ways in which the technology can be used in conjunction with other types of solar cell such as quantum dot and thin film photovoltaic technology.