Although wearables like smartwatches, fitness trackers and biomedical devices are becoming ever more commonplace, Timothy O’Connor at the University of California, San Diego, and his colleagues want to find ways to make them more discreet.

“These devices are still kind of clunky,” he says. “We’re trying to make these electronics almost imperceptibly integrated with the user.”

To do that, they have created a wearable solar power source that can handle the everyday bending and twisting of skin as we move about. O’Connor’s team switched out typical solar cell materials for a modified plastic that had been designed in the lab to be both flexible and conductive.

The final device, an adhesive patch around half the size of a credit card, is about 1% efficient at converting sunlight into energy. The team successfully used it to power an LED as well as a digital watch.

“It’s just like a bandage,” says O’Connor. “After demos, I would forget to take it off because I forgot I had it on.” In the future, they hope to build a solar cell that could be used in a small medical device like a glucose sensor.

The team isn’t the first to try putting solar cells in unusual places. Andrew Blakers, director of the Australian National University Centre for Sustainable Energy Systems in Canberra, has worked on lightweight cells that can be stitched into clothing and backpacks. Other scientists have successfully woven cells them into fibres.

Blakers is sceptical that wearable solar cells will go far, as conventional cells outstrip them in efficiency. “This looks like a solution looking for a problem,” he says.

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