A team of South Korean researchers has developed innovative new solar cells so thin that they can actually be wrapped around a pencil. Recently published in the Applied Physical Letters journal, the breakthrough could usher in an entire generation of flexible photovoltaics that could in turn power a range of electronics, including wearables like smart glasses and fitness trackers.
It is common knowledge that thin materials are significantly more flexible than thicker counterparts. When something is being bent, the stress buildup in the substance increases outward from its central plane. Since thick substances possess more material farther out, they are usually harder to bend or flex. Speaking about the research, Jongho Lee of South Korea-based Gwangju Institute of Science and Technology said:
Our photovoltaic is about 1 micrometer thick.
According to the team, one millimeter is even thinner than a single human hair. By comparison, currently-available solar cells are nearly hundred times thicker. What’s more, even those touted as thin photovoltaics are around 2 to 4 times greater in thickness than the newly-developed ones. The material, as the researchers point out, is fashioned out of the semiconductor gallium arsenide.
To ensure its flexibility, the team placed the cells directly onto a thin substrate without adding any kind of adhesive that would otherwise have increased the material’s thickness. Following this, the photovoltaic cells were “cold welded” to the substrate’s electrode, with the application of pressure at about 170 degrees Celsius. This in turn caused the top layer of the substance to melt, forming a temporary adhesive also known as photoresist.
Later on, the scientists removed the photoresist from the material, leaving behind the direct metal-to-metal bond. The substrate’s bottom layer, according to the researchers, acted as a reflector responsible for sending all stray photons back to the cells. When it comes to conversion efficiency, the new material was found to be at par with the thicker varieties currently available in the market.
To check its flexibility, the ultra-thin photovoltaics were subjected to bending tests, which showed that the cells could be easily wrapped around radius of less than 1.4 millimeters. The team performed what they are calling numerical analysis of the cells, according to which the substance experiences only one-fourth of the total strain occurring in photovoltaics that are around 3.5 micrometers in thickness. Lee added:
The thinner cells are less fragile under bending, but perform similarly or even slightly better.
The new technology could be used to power a variety of flexible electronics, including wearables. What’s more, these ultra-thin cells could be integrated into fabrics and glass frames, so as to capture sun’s energy with greater efficiency.