Wearable electronics woven into lightweight and flexible fabrics could be used to power portable devices, and applications such as electronic skin, smartwatches and bracelets have already seen the light of day. However, such applications are limited by the lifespan of their batteries.

“One way to overcome this problem is to directly integrate a conventional rechargeable-energy storage device, such as a battery or supercapacitor, into fabrics, explains team-leader Zhong Lin Wang. “However, such a self-powered system needs an efficient energy harvester and devices used in the past were strongly dependent on weather and working conditions.”

“To overcome this problem, we have now developed the first self-charging hybrid system that can scavenge two types of energy simultaneously from its environment.”

Three fibre-shaped components

The first component in the device harvests solar energy from ambient light and the second the mechanical energy that a person creates as he moves about during normal everyday activities. Both of these energies can easily be converted into electricity in fibre-shaped dye-sensitized solar cells (F-DSSCs) and fibre-shaped triboelectric nanogenerators (F-TENGs). The combined energy is then stored as chemical energy in a third component, fibre-shaped supercapacitors (F-SCs).

“Since all the components in our new system are shaped like fibres, they can easily be woven into electronic textiles to make smart clothes for driving wearable electronic devices,” explains Wang.

Double-layer structure

The double-layer structure of the hybridized self-charging power textile can be seen in the images above. The researchers used the F-DSSC-based component, which is made up of several F-DSCC units for harvesting solar energy, to build the top layer of the system. The advantage of using DSCCs is that they can be tuned to optimally function in a variety of lighting conditions, and so are suitable for indoor and outdoor applications. DSSCs can also be applied to a variety of substrates, including ones that support a TENG structure.

The F-SC-based textile for its part forms the bottom layer and each F-DSSC and F-SC unit is connected to one another to form a single F-TENG one.

A word on TENGs

TENGs work thanks to the triboelectric effect and electrostatic induction. They generate small amounts of electrical power from mechanical motion or external vibrations. The triboelectric effect occurs when certain materials become electrically charged after they come into moving contact with a surface made from a different material.

The electricity generated by TENGs could replace or supplement batteries for a broad range of potential applications and the technology, which has greatly improved over the last few years, is now good enough to power nanoelectronics devices.

The Georgia-Beijing team, reporting its work in Science Advances DOI: 10.1126/sciadv.1600097, is now busy improving the design of its device so that it can make a large-area fabric power cell. “We are also looking into how durable the structure is and hope to make it washable,” Wang told nanotechweb.org.