Solar cells that are transparent enough to be used to tint windows on buildings or cars, have been developed by U.S researchers.
Conventional solar cells are bulky and rigid but lightweight cells are usually far less efficient. However, a new method of making the silicon-based devices could create thin, flexible cells without any trade-offs.
Brittle wafers of silicon are sliced into ultra-thin pieces and carefully 'printed' onto a malleable surface. The cells are so flexible they can be rolled around a pencil.
'You can make (the solar cells) in the form of a gray film that could be added to architectural glass,' said lead researcher John Rogers of the University of Illinois.
'It opens up spaces on the fronts of buildings as opportunities for solar energy.'
The new technology could be used on car windows, generating enough electricity to power the GPS or air conditioning.
Solar cells, which convert solar energy into electricity, are in high demand because of higher oil prices and concerns over climate change.
Many international companies are making thin-film solar cells, but they are typically less efficient at converting solar energy into electricity than conventional cells.
Rogers said his technology uses conventional single crystal silicon. 'It's robust. It's highly efficient. But in its current form, it's rigid and fragile,' he said in the journal Nature Materials.
Rogers' team uses a special etching method that slices chips off the surface of a bulk silicon wafer. The sliced chips are 10 to 100 times thinner than the wafer, and the size can be adapted to the application.
Once sliced, a device picks up the bits of silicon chips 'like a rubber stamp' and transfers them to a new surface material, Rogers said.
'These silicon solar cells become like a solid ink pad for that rubber stamp. The surface of the wafers after we've done this slicing become almost like an inking pad,' he said.
'We just print them down onto a target surface.'
The final step is to electrically connect these cells to get power out of them, he said.
Adding flexibility to the material would make the cells far easier to transport. Rogers envisions the material being 'rolled up like a carpet and thrown on the truck.'
The technology has been licensed to a startup company called Semprius Inc in the U.S.
