(Invited) highly Stretchable Self-Powered Sensors Enabled By Vertically-Assembled 2D Materials

Abstract

Future electronics, such as human health monitoring systems, require highly stretchable strain sensors applicable to various types and ranges of motions. Two-dimensional (2D) materials exhibiting superior mechanical properties have a potential to achieve high range of strain compared to conventional devices and also realize self-powered sensing. In this talk, we present self-powered strain sensor with large stretchability enabled by graphene electrode layers and molybdenum disulfide (MoS2) active layer. In order to maximize the energy harvesting ability, flexoelectric effect was adopted in our device design. Flexoelectric effect induces an electric polarization from strain gradient, and the size of the strain gradient grows quadratically as the material’s length scale decreases. This scaling enables maximum flexoelectric effects in 2D materials with strain gradient. To realize the strain gradient in MoS2 active layer, we first prepared graphene-MoS2 vertical stack on a pre-stretched elastomeric substrate followed by a release of the stretch to create a crumpled heterostructure. The crumpled MoS2/graphene was again stretched to a smaller strain, and the other graphene electrode layer was placed on top of the crumpled MoS2 active layer. Releasing the strain after assembly resulted in a periodic contact between the top graphene electrode and the MoS2 active layer while maintaining a full contact between the bottom graphene electrode and the MoS2 active layer. Our stretchable flexoelectric graphene/MoS2/graphene device demonstrated voltage and current outputs under various mechanical deformations, including bending and stretch-release motions. Our results demonstrate self-powered strain sensing capability under high degree of bending and stretching motions, potentially applicable to human health monitoring sensors.