Flexible solar cells could be used in glasses frames

It was said that the solar cells, which are sufficiently flexible to wrap around the average pencil, could power wearable electronics like smart glasses and fitness trackers.The researchers reported the results in the American Institute of Physics’ (AIP) journal, Applied Physics Letters.According to the AIP, thin materials flex more easily than thick ones because the stress in a material while it is being bent increases farther out from the central plane. As thick sheets have more material farther out, they are harder to bend.Mr Jongho Lee, an engineer at the Gwangju Institute of Science and Technology in South Korea who was involved in the research, said the photovoltaic the team had developed was about 1 micrometre thick.By comparison, standard photovoltaics are usually hundreds of times thicker, and even most other thin photovoltaics are two to four times thicker.Mr Lee added that the thin cells could be integrated into glasses frames or fabric, with the potential to power the next wave of wearable electronics.The researchers made the ultra-thin solar cells from the siconductor 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 by applying pressure at 170 degrees Celsius and melting a top layer of material called ‘photoresist’ that acted as a tporary adhesive. The photoresist was later peeled away, leaving the direct metal-to-metal bond.The metal bottom layer also served as a reflector to direct stray photons back to the solar cells. 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 mm.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,” Mr Lee said.It was said that a few other groups had reported solar cells with thicknesses of around 1 micrometre, but they had produced the cells in different ways, for example, by roving the whole substract by etching.“By transfer printing instead of etching, the new method developed by Mr Lee and his colleagues may be used to make very flexible photovoltaics with a smaller amount of materials,” an AIP media statent explained.The full study is available via the Applied Physics Letters website.