Japanese and European researchers say they've developed solar cells thinner than a thread of spider silk and flexible enough to be wrapped around a human hair.

At just 1.9 micrometers in thickness, a 10th of the thinnest solar cells now available, they could find a number of new future uses, researchers said, including portable electrical charging devices or electronic textiles woven into clothing.

"Being ultra-thin means you don't feel its weight and it is elastic," researcher Tsuyoshi Sekitani from the University of Tokyo said.

"You could attach the device to your clothes like a badge to collect electricity [from the sun]. Elderly people who might want to wear sensors to monitor their health would not need to carry around batteries," he said in a report published the online science journal Nature Communications.

Researchers from Johannes Kepler University of Austria and from the University of Tokyo, who collaborated on the thin solar cells, say they believe they could be put to practical use within five years, Britain's Daily Telegraph reported.