Seoul: Scientists have made ultra-thin photovoltaic cells flexible enough to wrap around the average pencil that could power wearable electronics like fitness trackers and smart glasses. "Our photovoltaic is about 1 micrometre, thinner than an average human hair," said Jongho Lee, an engineer at the Gwangju Institute of Science and Technology in South Korea. Standard photovoltaics are usually hundreds of times thicker and even most other thin photovoltaics are two to four times thicker. The researchers made the ultra-thin solar cells from the semiconductor gallium arsenide. They stamped the cells directly onto a flexible substrate without using an adhesive that would add to the material's thickness. The cells were then "cold welded" to the electrode on the substrate. The researchers tested the efficiency of the device at converting sunlight to electricity and found that it was comparable to similar thicker photovoltaics. They performed bending tests and found the cells could wrap around a radius as small as 1.4 millimetres. The team also performed numerical analysis of the cells, finding that they experience one-fourth the amount of strain of similar cells that are 3.5 micrometres thick. "The thinner cells are less fragile under bending, but perform similarly or even slightly better," Lee said in a paper published in the journal Applied Physics Letters. These thin cells can be integrated onto glasses frames or fabric and might power the next wave of wearable electronics, Lee noted.