Nanoscientists are working on some bright ideas to develop cost-efficient materials that can be used to produce and store energy more efficiently – but are they viable?

Duncan Graham-Rowe  guardian.co.uk, Tuesday 20 September 2011 14.28 BST

Can nanotechnology provide cheaper solar energy?

Nanoscientists are working on some bright ideas to develop cost-efficient materials that can be used to produce and store energy more efficiently – but are they viable?

It is hard to ignore the escalating price of oil. It is not just the hole that it is burning in our pockets on the forecourt; the increasing scarcity and lack of security surrounding oil and gas is also helping to push up the overall cost of living, from heating our homes to the price of everyday consumer products. Even medicine and food now cost more because of oil.

Against this background, scientists and engineers believe that the development of novel nanomaterials may hold the key to help us reverse this trend, by enabling us to produce and store energy more efficiently.

One prime example of this is solar energy. Despite decades of development, solar cells are still relatively expensive. This not only makes solar an unattractive and uncompetitive alternative to fossil fuels, but it ensures that the technology is not deployed where it is most needed, says Ineke Malsch of Malsch TechnoValuation, a consultancy based in Utrecht, the Netherlands, that specialises in assessing emerging technologies.

"There is already a technology gap between rich and poor countries," she says. "People living with no grid electricity will benefit more from solar cells than those living in places like London." Nanotechnology has the potential to redress this imbalance by bringing down the cost of solar energy, says Malsch.

One of the reasons for the high cost of traditional semiconductor photovoltaic solar cells is their poor design, says Milo Shaffer, co-director of the London Centre for Nanotechnology, at Imperial College.

The most efficient cells tend to be made up of layers of expensive crystalline silicon. These have chemicals added to encourage particles of light, called photons, to liberate electrons, which pass from one layer to the other to create a current. While this works, it could be done using cheaper materials and in ways that are more efficient, says Shaffer.

The amount of energy converted from light into electricity ultimately depends upon how many electrons can pass across the interface between the two layers. And this is limited by the size of that interface, he says. One way nanotechnology can help is by increasing the size of these interfaces by creating incredibly bumpy surfaces. "What you are trying to do is create very high surface areas at the interface," says Shaffer. This allows more electrons to pass, increasing the amount of electricity produced.

One kind of new solar cell that does precisely this is the dye-sensitised solar cell, or Graetzel cell. Instead of using two layers of silicon these solar cells consist of a highly porous layer of titanium dioxide nanoparticles, a common white material often used in paint, coated in a molecular dye (the molecules of which use sunlight to mimic chlorophyll and create energy). These cells are more flexible than traditional solar cells, they can work in higher temperatures and they can operate even in low-lighting conditions; but the key benefit is the size of the interface and thus the potential to create energy. Because of its porous nature the amount of surface area covered by the dye is much larger than the apparent area of the cell, says co-inventor Michael Graetzel at the Swiss Federal Institutes of Technology, in Lausanne. "You increase the surface area by at least a thousand times," he says.

It's a highly effective trick, and one which is also being used to create extremely high-surface areas in new kinds of batteries that can store many times more energy than existing cells, but which can be charged in the blink of an eye. And similarly ultraporous nanomaterials are being developed to help find ways of storing hydrogen at high densities for fuel-cell powered cars.

Further down the line, Nasa's Jeremiah McNatt is leading on an approach that uses quantum dots – small semiconductor particles just a few nanometres in size – to help boost the performance of solar cells even further. The aim here is to replace the heavy, fragile solar cells that are currently used by spacecraft with ones that incorporate a mixture of organic and inorganic nanostructured materials, to make ultra-lightweight and flexible solar cells.

But with this kind of technology also come new concerns. "As you approach the nanoscale, things behave differently," says David Koepsell, a philosopher at Delft University in the Netherlands, and author of Innovation and Nanotechnology: Converging Technologies and the End of Intellectual Property. This is half the attraction of using nanomaterials, but it has also led to fears that materials that are benign in ordinary form could be hazardous when nano-sized. Because of this, existing regulations may not be enough to cover nanomaterials, he says.

For workers involved in the manufacturing or disposal of these kinds of solar cells, a degree of caution may be warranted to ensure their safety and the safety of the environment. In light of this, the European Commission has created a code of conduct to address issues such as sustainability, accountability and what precautions need to be put in place when developing nanotechnologies. In order to implement the code of conduct, the NanoCode project has been set up to identify best practices from research labs so they can be applied not only to manufacturing, but to the whole lifecycle of a product.

The bottom line, according to Malsch, is if you treat these nanoparticles as though they are hazardous materials and take measures to ensure they are contained during manufacture and disposal, then you can avoid any unpleasant surprises in the years to come.

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