Ultra-Flexible Piezoelectric Nanogenerator and Mechanical Bending Sensor Using Solution Processed ZnO Nanomaterials

Abstract

With world-wide crisis of energy resources depletion and global warming, exploring of renewable green energy matches the upsurge of interest in scientific fields. On the larger scale, petroleum, coal, natural gas, hydroelectric and nuclear are the well-known current world energy resources, which are now in mortal danger for their shortage. However, development of alternative energy such as solar, wind, geothermal, hydrogen, and biomass has recently been flourished. However, on the smaller scale, requiring the entire packages in nanometer scale, the nano energy system is applicable to personal mobile electronics, micro- electromechanical systems, nanorobotics, and body implantable devices. For portable, light-weighted device as well as persistent use without batteries, self- powered system should be adopted in a field of energy harvesting and sensing technologies. In this regard, piezoelectric nano-elements can be a fundamental solution to offer self-powered active system for driving wireless and mobile electronics. Piezoelectric nanodevice that converts mechanical energy into electricity is emerging field in recent energy researches because of availability of destroyed energy from ambient environment. Adopting this piezoelectric energy conversion theorem is promising for power generation in new method form for the future. The first piezoelectric nanogenerator was invented by Z. L. Wang et al., which was demonstrated using ZnO nanowire array in 2006. ZnO is particularly appealing material because of its coupling effect of piezoelectric and semiconducting properties, high elasticity, abundant configurations of nanostructure, transparency, and biocompatibility. However, ZnO nanomaterials are mostly synthesized via vapor liquid solid method or sputtering with vacuum process, which requires high cost and complex equipment system. Solution process of ZnO nanomaterials has advantages for simple and low cost, and also can be deposited over a large area with mass production. In this point of view, I demonstrated piezoelectric nanodevices with solution processed ZnO nanomaterials and analyzed the output performance as well as the mechanism of the piezoelectric phenomena. Firstly, using solution-processed ZnO thin film, an ultra-flexible piezoelectric patch-shaped nanogenerator was demonstrated for use as embedded muscle or cloths scavengers. The entire process of the patch, also called as nanogenerator, was conducted by solution process including piezoelectric active material, electrodes, and p-type polymer blend for efficient piezoelectric energy generation. The highly elastic thin film nanogenerator allowed piezoelectric energy generation through mechanical rolling and muscles stretching of human arms. Secondly, using solution-processed ZnO nanorods, a piezoelectric bending motion sensor was developed for simultaneous recognition of bending curvature and speed with systematic analysis based on a database of output performance with statistical measurement. For bendability, a polydimethylsiloxane sandwiched ZnO nanorods layer was adapted as well as hybrid electrode of flexible Ag nanowire and single-wall carbon nanotubes. This highly bendable piezoelectric bending motion sensor is expectable for the realization of artificial skin, wearable electronics, and biomimetic robot system. In summary, via solution processing of ZnO nanomaterials, piezoelectric active material was synthesized and applied to ultra-flexible nanogenerator and sensor to fabricate piezoelectric nanodevices for versatile, cost-effective system. These piezoelectric nanodevices have potential to be integrated into multi-functional nanosystem with self-powered capability.