117955_web
June 20, 2016

Researchers develop new ultra-thin, flexible solar cells

A team of engineers at the Gwangju Institute of Science and Technology in South Korea have reportedly developed a new kind of ultra-thin, bendable solar cell capable that could be used to power fitness trackers, smart glasses and other kinds of wearable technology.

In fact, their photovoltaic technology is said to be flexible enough to wrap around the average pencil, developer Jongho Lee and his colleagues explained in a statement. Their breakthrough, which is reported in detail in Monday’s issue of the journal Applied Physics Letters, utilizes a special technique that allows it to be thin and flexible while requiring fewer materials.

The solar cell is approximately one micrometer thick, or thinner than the typical human hair. In contrast, standard photovoltaics are usually several hundred times thicker, and even other kinds of thin cells are at least twice as big. The thinness of the material makes it easier to flex because it has less material at the farthest ends of the central plane than thicker photovoltaic sheets.

Lee’s team constructed the solar cells from a semiconducting material called gallium arsenide, and stamped them directly onto a flexible substrate without using an adhesive, as doing so would have increased the thickness of the material.

Photovoltaics could be used to power next-gen wearable technology

These cells were then “cold welded” to the electrode on the substrate by applying pressure at a temperature of  338 degrees Fahrenheit (170 degrees Celsius) and melting a temporary adhesive known as photoresist onto the top of the newly-assembled unit.

Eventually, the layer of photoresist was peeled away, leaving the direct metal to metal bond that also served as a way to reflect stray photons back onto the solar cells. Efficiency tests of the cells revealed that they were comparable to other, thicker photovoltaics, while also being able to wrap around an object with a radius as small as 1.4 millimeters (0.055 inches).

In addition, Lee’s team analyzed the cells and found that they experience just 25% the amount of strain as similar solar cells that are 3.5 micrometers thick. These new, thin photovoltaics are “less fragile under bending, but perform similarly or even slightly better,” Lee said. While other teams of researchers have reported success with solar cells roughly one micrometer thick, the new cells are assembled using a novel new method.

Rather than using the etching process to remove the entire substrate, the GIST-led team instead uses transfer printing to develop extremely flexible photovoltaics while using a smaller quantity of materials, the researchers explained. The new cells are so thin and flexible that they could be integrated into the frames of smart glasses or the fabrics used to make wearable technology, they added.

-----

Image credit: Juho Kim, et al/ APL