ZnO-based Nanogenerators Research Articles

Metal-doped zinc oxide nanostructures for nanogenerator applications: A review

Nanogenerators have been widely discussed and investigated in the literature due to their excellent development in various sectors and applications. There are two typical electricity generating mechanisms involved in nanogenerators, that include piezoelectric and triboelectric processes. The selection of materials in developing nanogenerator applications is vital in guaranteeing that the produced devices have decent output performance. Zinc oxide (ZnO) is a semiconductor material with a large bandgap that significantly influences numerous technological sectors, including nanogenerator fabrications. Besides, numerous methods have been used to synthesize ZnO nanostructures for various applications. The improvement and alterations need to be performed based on the produced ZnO nanostructures for better device performance. Previous studies have reported the effect of metal-doped ZnO nanostructures on the properties and characteristics of the nanogenerator applications. Hence, the brief review of the different techniques used in the fabrication of ZnO nanostructures and the performance enhancement of the ZnO-based nanogenerator, which consists of the doping process and the development of nanogenerator applications, have been presented in this paper.

Direct-current piezoelectric nanogenerator based on two-layer zinc oxide nanorod arrays with equal c-axis orientation for energy harvesting

Direct current (DC) piezoelectric nanogenerators, that can harvest mechanical energy into electrical power, have been extensively studied for driving low-power electronic devices without pre-rectification. However, the output power of most developed DC generators is generally too low to satisfy the requirements of diverse micro-electronic devices. Herein, we design a high-output Schottky DC nanogenerator consisting of a top gold electrode, the piezoelectric layer of zinc oxide (ZnO) nanorod arrays grown on polarized polyacrylonitrile film, a bottom copper electrode with ZnO nanorod arrays, where the crystallographic c-axis orientation of both ZnO nanorod arrays trends to be the same. The fabricated DC nanogenerator shows the peak voltage and current density as high as 1.6 V and 7.2 μA/cm2, respectively, which are several times higher than that of a pure ZnO-based nanogenerator. It has been demonstrated to harvest ambient tiny mechanical energy, including human activity, impact/collision, and sound vibration, to power commercial microelectronics directly, and to charge a storage capacitor for driving a heath-care device. Such novel DC nanogenerator may have great application prospects in self-powered electronics, structure and human health monitoring, and many more places.

Enhanced piezoelectric performance of the ZnO/AlN stacked nanofilm nanogenerator grown by atomic layer deposition

The ZnO-based nanogenerators (NGs) with a precisely controlled interlayer of AlN are fabricated based on atomic layer deposition technique, which was proved to possess an enhanced output signal. The microstructure and composition profiles of the prepared ZnO/AlN stack layer are well characterized first. It was found that the piezoelectric performance of ZnO/AlN stacked nanofilm NGs depends strongly on the thickness of AlN. The maximum piezoelectric open circuit output voltage of 4.0 V and output power of 2.42 µW have been achieved with an optimum 2.3 nm thick AlN interlayer. The piezoelectric output of the NGs also relates with the value and the frequency of the compressive force. The inherent mechanism for the improvement of piezoelectric performance in the stacked structure is well discussed. The findings are expected to provide a simple, inexpensive, and effective approach for enhancing the performance of ZnO-based NGs.

A comparative study on a flexible ZnO-based nano-generator using Schottky and p–n junction contact for energy harvesting applications

Vibration based piezoelectric energy harvesting from unused ambient sources is an efficient approach for a battery-free, sustainable and green power source for self-powered electronics. This paper presents the performance enhancement of a p-n junction based flexible nano-generator (NG). A stable, non-hazardous spiro and zinc oxide (ZnO) p-n junction based NG is proposed. The device performance is compared with a Schottky contact based NG. The experimental study is carried out using the tip excitation method. Most importantly, the contact modification with spiro improves the performance of the device by five times, thereby yielding an open circuit voltage of 300 mV, a short-circuit current density of 220 μA cm-2 and a maximum power density up to 48 μW cm-2 at 0.5 N. Furthermore, performance enhancement is achieved by reducing the external screening and the internal impedance. The results are validated using an RC time constant value derived from the impedance analysis.

An electrostatic nanogenerator based on ZnO/ZnS core/shell electrets with stabilized quasi-permanent charge

ZnO-based nanogenerators with excellent performance and convenient functionalization are particularly desirable for self-powered technology, which is however difficult to achieve simultaneously in traditional piezoelectric ZnO nanogenerators. Here, we report a design of electrostatic ZnO nanogenerator by virtue of a type-II ZnO/ZnS core/shell nanostructure electrets, which can turn acoustic waves into electric power with an energy conversion efficiency of 2.2%. The ZnO/ZnS core/shell electrets are charged by ultraviolet irradiation with a long-term stability of the electrostatic charges under ambient condition. The electronic and atomic structure evolution in the charged ZnO/ZnS core/shell electrets are also discussed by detailed experimental and theoretical investigations. This design opens up an alternative path for fabricating robust ZnO-based nanogenerator for future nanotechnology application.