Paper solar cells can be folded away and used when required

At present, the paper solar cells have an efficiency of about one per cent — enough to power ‘small electric gizmos’ — but the team believes this can be increased significantly with the further fine-tuning of the materials.

‘We have demonstrated quite thoroughly the robustness of this technology,’ said collaborator Prof Vladimir Bulović of MIT. ‘We think we can fabricate scalable solar cells that can reach record-high watts-per-kilogramme performance.’

The new printing process uses vapours, not liquids, and temperatures of less than 120ºC. These ‘gentle’ conditions make it possible to use ordinary untreated paper, cloth or plastic as the substrate on which the solar cells can be printed.

However, in order to create an array of photovoltaic cells on the paper, five layers of material need to be deposited onto the same sheet of paper in successive passes, using a mask (also made of paper) to form the patterns of cells on the surface. In addition, the process has to take place in a vacuum chamber.