Charge‐Generating Mode Control in High‐Performance Transparent Flexible Piezoelectric Nanogenerators

Abstract

In this work, we demonstrate the mode transition of charge generation between direct‐current (DC) and alternating‐current (AC) from transparent flexible (TF) piezoelectric nanogenerators (NGs), which is dependent solely on the morphology of zinc oxide (ZnO) nanorods without any use of an AC/DC converter. Tilted ZnO nanorods grown on a relatively low‐density seed layer generate DC‐type piezoelectric charges under a pushing load, whereas vertically aligned ZnO nanorods on a relatively high‐density seed layer create AC‐type charge generation. The mechanism for the geometry‐induced mode transition is proposed and characterized. We also examine the output performance of TF‐NGs which employ an indium zinc tin oxide (IZTO) film as a TF electrode. It is demonstrated that an IZTO film has improved electrical, optical, and mechanical properties, in comparison with an indium tin oxide (ITO) film. Enhanced output charge generation is observed from IZTO‐based TF‐NGs when TF‐NGs composed of only ITO electrodes are compared. This is attributed to the higher Schottky barrier and the lower series resistance of the IZTO‐based TF‐NGs. Thus, by using IZTO, we can expect TF‐NGs with superior mechanical durability and power generating performance.

Oriented Morphogenesis of ZnO Nanostructures from Water‐Soluble Zinc Salts under Environmentally Mild Conditions and Their Optical Properties

“…[14][15][16] Instead, our efforts have been focused towards using simple, positively charged polypeptides and related polyamines, which resemble biosilicification agents in diatoms, to synthesize and assemble nanomaterials under environmentally benign conditions. [17,18] Although this approach has led us to fabricate ZnO spindles and rods in a wet-chemical method, the process requires prior formation of Zn(OH) 2 and a longer reaction time (15 h). [18] Herein, we report our bottom-up approach utilizing water-soluble zinc salts for the mineralization of ZnO nanostructures in a very simple and versatile process.…”

“…[1][2][3][4][5][6] Hence, a great deal of effort has been devoted to the development of new methodologies for the synthesis of ZnO nanostructures with tailored sizes and morphologies under mild conditions to tune their optical, electrical, and catalytic properties. Moreover, such sustainable methods are essential for growing these nanostructures on flexible substrates, which would be particularly significant for making flexible, lightweight, portable, and high-performance functional devices.…”

One-dimensional ZnO nanostructures: Solution growth and functional properties

“…Therefore, by replacing the Si wafers with flexible and transparent conducting electrodes, such as ITO deposited on plastic substrates [499,544], carbon nanotube networks [545], and graphene [546][547][548], rollable and transparent nanogenerators can be fabricated as power sources for touch sensors, artificial skins, and wearable personal electronics.…”

Fabrication and photocatalysis of ZnO nanotubes on transparent conductive graphene-based flexible substrates

“…However, the large band gap and the massive recombination of photogenerated charge carriers, especially in its nanosize, limit the overall photocatalytic efficiency. Intensive studies have demonstrated new applications such as piezoelectric nanogenerators, self-powered piezotronic strain sensors and Schottky contact-based nanosensors using 1D ZnO nanotubes (NTs) [11][12][13][14]. Substantial effort has been devoted to the development of novel synthetic methodologies for 1D ZnO NTs [15][16][17][18][19].…”