Wearable electronics are quickly becoming the fashion.
And there could soon be a way to power those electronics indefinitely with a new development that weaves solar cells into clothes. The textile retains a power-generation efficiency close to 1 percent even after been bent more than 200 times, and can be illuminated from both sides.
Scientists have been looking into flexible solar cells for decades, partly for coating irregularly shaped objects but also for integrating into wearable fabrics. One popular line of investigation has been dye-sensitized solar cells, in which a pigment absorbs sunlight to generate electrons and their positive counterparts, holes, before passing on those charges to inexpensive semiconductors.
These solar cells are cheap and flexible, but the liquid nature of their pigments means they must end up well sealed. Bend a dye-sensitized solar cell more than a few times and the seals are likely to break, destroying its light-harvesting properties.
That is why Huisheng Peng at Fudan University in Shanghai, China, and colleagues have been exploring another option: Polymer solar cells.
Although their maximum efficiencies fall below 10 percent – about half that of crystalline silicon, the most prevalent solar cell – polymer solar cells are lightweight, flexible and easy to manufacture.
Peng and colleagues’ solar cell textile consists of microscopic interwoven metal wires coated with an active polymer (to absorb the sunlight), titanium dioxide nanotubes (to conduct the electrons) and another active polymer (to conduct the holes). The researches coated each side of the textile with transparent, conductive sheets of carbon nanotubes, which complete the circuit.
Because of the textile’s symmetry, it is possible to illuminate the cell on either side. In tests it exhibited a maximum efficiency of 1.08 percent, which varied by less than 0.03 percent after 200 cycles of bending. However, the textile is currently only about the size of a fingernail. ‘The main difficulties encountered are how to scale up the solar-cell textile while maintaining high energy-conversion efficiencies,’ Peng said.
Materials scientist Anyuan Cao, who was not involved with the work, believes the results show promise, particularly the use of carbon nanotube sheets to allow illumination from both sides. But he said wearable solar cells are still a ways off. “Current textiles demonstrated in laboratories are too small and have low energy conversion efficiencies,” Cao said, who is at Peking University in China. ‘The materials involved and the fabrication processes are still expensive. Practical use not only requires that the textiles should withstand simple bending, but also that they should sustain much more complex deformations such as folding and twisting, even under dynamic conditions.’
Peng said he and his colleagues are now working to increase the energy-conversion efficiency of their solar cell textile.