Skin‐Integrated Graphene‐Embedded Lead Zirconate Titanate Rubber for Energy Harvesting and Mechanical Sensing

Abstract

Thin, soft skin-integrated electronics have attracted great attentions due to their advantages such as flexible, lightweight, and mechanical compatible with human body, thus offer unique capabilities in detecting vital information and continuous monitoring human health.[1–8] Recent advances in materials development,[9–15] electronics miniaturization,[16–20] mechanics optimization,[18,21–24] and system-level integration[17,25–28] build up the foundations for flexible and stretchable electronics[29–32] which are able to be integrated together with skin. Considering power supply for this new kind of soft electronics, conversion of mechanical energy from human body activities and motions to electricity is a considerable route.[4,5,13,33,34] Various kinds of technologies, such as piezoelectric,[35–40] triboelectric,[41–47] electromagnetic,[48] and pyroelectric[49–51] have been considered and studied. Among these self-powered technologies, piezoelectric generators have proven to be a great candidate as energy harvesters for skin-integrated or even biointegrated electronics, due to the combination of their excellent electrical properties and advanced mechanical designs.[5,18,52,53] Materials and mechanical engineering in piezoelectric materials, including lead zirconate tinanate (PZT),[1,11,18,19,24,38] PVDF,[20,21,53] BaTiO3, NaNbO3, and ZnO[35,56] have been made great progress and realized outstanding electromechanical properties. However, complicated fabrication processes involving high temperature deposition, multiple steps photolithographs, physical/chemical etchings, and transfer printings are typically needed to meet the requirement of flexibility.[17,18,57–59] To realize rapid and low-cost processing techniques for soft piezoelectric based electronics, inherent flexibility of the materials should be carefully considered, as which affords the possibility for large-area fabrication relevant routes, such as screen-printing and roll to roll technologies.[9] One promising method for realizing inherent flexible piezoelectric materials is designing polymer-matrix composites which typically consist of piezoelectric ceramic powders and silicone rubbers (polydimethylsiloxane, PDMS).[11,15,60–63] This Thin, soft, skin-like electronics capable of transforming body mechanical motions to electrical signals have broad potential applications in biosensing and energy harvesting. Forming piezoelectric materials into flexible and stretchable formats and integrating with soft substrate would be a considerable strategy for this aspect. Here, a skin-integrated rubbery electronic device that associates with a simple low-cost fabrication method for a ternary piezoelectric rubber composite of graphene, lead zirconate tinanate (PZT), and polydimethylsiloxane (PDMS) is introduced. Comparing to the binary composite that blend with PZT and PDMS, the grapheneembedded ternary composite exhibits a significant enhancement of selfpowered behavior, with a maximum power density of 972.43 μW cm−3 under human walking. Combined experimental and theoretical studies of the graphene-embedded PZT rubber allow the skin-integrated electronic device to exhibit excellent mechanical tolerance to bending, stretching, and twisting for thousands of cycles. Customized device geometries guided by optimized mechanical design enable a more comprehensive integration of the rubbery electronics with the human body. For instance, annulus-shape devices can perfectly mount on the joints and ensure great power output and stability under continuous and large deformations. This work demonstrates the potential of large-area, skin-integrated, self-powered electronics for energy harvesting as well as human health related mechanical sensing.