Embossed hollow hemisphere-based piezoelectric nanogenerator and highly responsive pressure sensor

Harvesting energy using piezoelectric materials such as ZnO, at nanoscale due to geometrical effects, are highly desirable for powering portable electronics, biomedical, and healthcare applications. Although one-dimensional nanostructures such as nanowires have been the most widely studied for these applications, there exist a limited number of piezomaterials that can be easily manufactured into nanowires, thus, developing effective and reliable means of preparing nanostructures from a wide variety of piezomaterials is essential for the advancement of self-powered devices. In this study, ZnO embossed hollow hemispheres thin film for highly responsive pressure sensors and nanogenerators are reported. The asymmetric hemispheres, formed by an oblique angle deposition, cause an unsymmetrical piezoelectric field direction by external force, resulting in the control of the current direction and level at about 7 mA cm^-2 at normal force of 30 N. The nanogenerators repeatedly generate the voltage output of ≈0.2 V, irrespective of the degree of symmetry. It is also demonstrated that when one piece of hemisphere layer is stacked over another to form a layer-by-layer matched architecture, the output voltage in nanogenerators increases up to 2 times.