Austrian and Japanese researchers on Wednesday unveiled solar cells thinner than a thread of spider silk that are flexible enough to be wrapped around a single human hair.

The thin-film device, comprising electrodes on a plastic foil, is about 1.9 micro-metres thick, a tenth the size of the thinnest solar cells currently available, the researchers said.

One micro-metre is one millionth of a metre (3.3 feet).

"The total thickness of this device is less than a typical thread of spider silk," the researchers said in a report carried by online science journal Nature Communications.

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

"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," Sekitani told AFP.

The research was done jointly by Martin Kaltenbrunner, Siegfried Bauer and other researchers from Johannes Kepler University of Austria as well as Sekitani and other contributors from University of Tokyo.

Sekitani said it was possible to make the cells bigger.

"Power generation by solar cells increases with their size. As this device is soft, it is less prone to damage by bending even if it gets bigger," he said.

Sekitani said the team hoped to increase the rate at which the device converts sunlight into electricity and put it to practical use in around five years.