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Over the past decade, researchers have developed many types of portable and flexible electronics, such as roll-up displays and electronic skins. However, providing an equally flexible and thin power source for these devices has proven more difficult. One potential source of energy is self-powering nanotechnology, aimed at harvesting energy from the environment to create a sustainable self-sufficient power source. Similar energy harvesters have already been used to turn flags into loudspeakers and to generate energy from the human body to power medical devices. Now, researchers, led by Dr Zhon Lin Wang at the Beijing Institute of Nanoenergy and Nanosystems and the Georgia Institute of Technology, have succeeded in making a soft, skin-like material capable of converting mechanical or biomechanical motion into electrical energy.

The stretchable, transparent energy harvester (technically known as a biocompatible triboelectric nanogenerator) is made by sandwiching a layer of ionic hydrogel, (which acts as an electrode) between two elastomer films, (which act as an electrification layer). Once the elastomer layers are electrified, static charges build up on their surface, driving the flow of current. Unlike previous nanogenerators, the new device uses an ionic, rather than an electrical, conductor as the electrode. This allows for greater stretch and transparency. The new energy harvester will also work in temperatures of up to 86 degrees fahrenheit (30 degrees celsius) and in humid conditions, which in the past has led similar devices to deteriorate.

The energy harvester can be used to drive wearable electronics by converting energy from mechanical motion such as hand tapping. As the device is also pressure-sensitive, applications for the harvester might include use in artificial electronic skin for sensing touch. Possible future uses include self-powered electronic skins for soft robots, touchscreens and wearable electronics. What other uses can be envisioned for a transparent, flexible energy harvester?