With the rising popularity of wearable electronics such as smart glasses and fitness trackers, thin and flexible solar cells can help make these gadgets more self-powered.

An ultra-thin solar photovoltaic cell developed by scientists in South Korea could just be this technology. The photovoltaic is so thin and flexible it can be wrapped around a pencil.

Gwangju Institute of Science and Technology engineer Jongho Lee said that the photovoltaic cell measures only 1 micrometer thick, which is far thinner when compared with a strand of human hair.

In comparison, average thin-film solar cells measure between 2 and 4 micrometers thick. Standard photovoltaics, on the other hand, are a hundred times thicker.

The extra thinness of the new photovoltaics allows it to be wrapped around things so small. Thin materials are more flexible than the thick ones because the stress in a bent material increases farther out from the central plane. Thick sheets tend to be more difficult to bend because they have more material farther out.

Lee and colleagues created the solar cells using the semiconductor gallium arsenide. They were able to bond the cells directly into a flexible substrate sans using a bulky adhesive by applying pressure at a temperature of 170 degrees Celsius.

The so-called cold-welding process created a temporary adhesive that could later be peeled away leaving direct metal to metal bond.

"The transfer-printing process reported here, providing a yield close to 100%, makes direct electrical interconnection possible with metal electrodes on substrates," the researchers reported in their study, which was published in Applied Physics Letters on June 20.

"This method does not require thick contact layers for the bottom electrodes, thus enabling efficient photon recycling in a thinner structure with back reflectors."

The researchers said that despite the thinness of the cells, they were found to be less fragile and perform comparable to or even better than thicker cells

Lee and colleagues tested the device to see how efficient it is in converting sunlight to electricity and found that its efficiency is comparable to those of similar but thicker solar cells. Bending tests likewise revealed that the cells are able to bend around radius as small as 1.4 millimeters.

While larger and more rigid panels may still be needed for large scale power generation, thin and bendable solar panels that can be placed on and bent around virtually any surface could have a range of applications particularly in wearable electronics and space industries.

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