(Invited) Flexible Nanogenerators for Energy Harvesting and Self-Powered Biomedical Devices

Abstract

Recently, flexible electronics have experienced a rapid development and are dramatically desirable for commercial, medical, and military applications. Conventional flexible biomedical sensors usually require external power-supply devices whose small power density and limited lifetime dramatically hinder the speedy advancement of this field. To solve the above issues, self-powered sensing technology has been introduced and attracted significant interests as a crucial alternative. The self-powered active sensor will generate electricity as a response to the external stimuli and the electric signal can reversely reflect the impact of the outside trigger. Therefore, it is able to effectively and independently work without any external power sources and hence its accelerated progress is of great significance to the prevalence of wearable and flexible sensors. Originated from Maxwell’s displacement current, nanogenerator (NG) based on triboelectric effects have been developing rapidly for efficiently harvesting environmental mechanical energy and self-powered active sensor. Triboelectric nanogenerator (TENG) relied on a conjunction of triboelectrification and electrostatic induction has shown numerous advantages, including large output, high efficiency, low cost, simple fabrication, light weight, and being environmental friendly. Besides mechanical energy, thermal energy is another important energy source especially for wearable electronics. The temperature difference (ΔT) between human body and surrounding environment always exists and can be used as driving force for electric energy generation through Seebeck effect. But the ΔT need to be furtherly enhanced. In our living environment, in addition to the direct heat source, light source (such as the infrared light) can also provide thermal energy through the photothermal effect. Based on the photothermal effect and Seebeck effect, photo-thermoelectric generator has been rapidly developed for converting photo energy into electricity without a spatial temperature gradient in the environment. In our works, flexible NGs based on triboelectric effect and photo-thermoelectric effect have been demonstrated and designed for wearable electronics. The electric signals obtained from the NGs not only can be acted as direct energy sources for flexible devices but also used for self-powered biomedical applications, such as human motion monitoring, temperature sensing, anti-bacterial treatment, and so on.