Charge your Cell phone with a beach towel

Scientists are improving on technology that would make it possible to generate energy by simply painting a liquid onto a surface, beach towel. Conventional solar cells are expensive to make. One type, for example, is made using a technique called vapour deposition, in which a photovoltaic material is laid down on a surface at very high temperatures, and often in a vacuum.

With a view to bringing costs down, Brian Korgel and colleagues at the University of Texas at Austin have developed a light-harvesting ink containing nanocrystals of copper indium diselenide. This can be sprayed onto a range of surfaces at room temperature using an airbrush. "It's essentially how you might paint your wall, except the pigment has a purpose," says Korgel.

The obstacle that Korgel and his team are currently trying to overcome is the rate of conversion; light into electricity: “Our best efficiency in the lab is just over 3 per cent,” he said. Photovoltaic liquids are only commercially viable if they convert at least 7 per cent, said Harry Atwater at the California Institute of Technology. To achieve a higher conversion rate the spray-on cells can be stacked on top of each other. This increases the rate to about 4.5 per cent.