Sci. Adv. 3, e1700015 (2017)

Power generation from body movement in an energy harvester entails stable performance over long periods of time under variable mechanical strain. A triboelectric nanogenerator (TENG) — a device that converts mechanical energy into electricity — is naturally flexible and, thus, has the ability to fulfil the required functionality. Now, Pu et al. have fabricated a soft and ultrastretchable on-skin triboelectric nanogenerator (STENG) that can simultaneously serve as a tactile sensor and energy harvester.

Unlike a conventional TENG designed with electrical conductors, the electrode of its skin-like analogue is composed of ionic hydrogel. In a typical STENG, a layer of PAAm-LiCl hydrogel is sandwiched between PDMS or VHB elastomer films that serve as electrification layers. The devices are nearly transparent in the visible range, biocompatible and can be stretched to more than ten times their original length without rupturing. The electrical performance doesn't show any signs of degradation after thousands of long-term motion cycles. The encapsulation of the hydrogel by the elastomers prevents its dehydration, preserving the device functionality in the temperature range of 0–60 °C. The on-skin generators are capable of producing an open-circuit voltage of 145 V and a power density of 36 mW m−2. Apart from the ability to harvest biomechanical energy, STENGs can serve as touch sensors, sensing pressure of as low as 1.3 kPa.