Improved Output Performance of Direct‐Current Triboelectric Nanogenerator through Field Enhancing Breakdown Effect

Abstract

As the world enters the new era of Internet of Things, big data, and artificial intelligence, widely distributed sensor networks with the characteristics of a random distribution, enormous amounts of data, and mobile and wireless communications have led to an increased energy demand, and a constant current power supply is required to drive their continuous operation. It is extremely challenging to solve these formidable problems using batteries owing to the disadvantages of a limited lifespan, non-negligible maintenance costs, and in particular, environmental pollution. In recent years, ambient energy harvesting technologies have become a sustainable, clean, and promising strategy for the distribution of energy demand, and various types of generators have been developed based on different working mechanisms, such as solar cells, electromagnetic generators, thermoelectric generators, piezoelectric generators, and triboelectric nanogenerators (TENGs).[1] Among them, the conversion and utilization of mechanical energy are undoubtedly considered one of the most promising choices owing to its wide distribution and variety of forms. In 2012, the TENG was invented by Prof. Wang’s group based on the coupling of contact electrification and electrostatic induction, and has been demonstrated as a promising strategy to convert random, distributed, and low-frequency mechanical energy into electric energy owing to the merits of a low cost, broad material selection, and diverse structural design.[2–6] In general, the output characteristics of conventional TENGs are an alternating current (AC) and pulse,[7] which cannot drive electronic devices directly. To solve these problems, many studies have been proposed to produce a direct current (DC), which is mainly divided into two categories. One is utilizing the power management unit,[8,9] mechanical rectifier,[10,11] and phase control[12–15] to realize DC output and a low crest factor (the crest factor is defined as the ratio between the peak current and the root-mean square value), which may increase the complexity of the system and inevitably cause an energy loss. The other category is based on the “self-rectified” principles, such as a Schottky knot,[16,17] silicon p-n junction,[18,19] contact barrier between metal and semiconductor,[20] The emerging direct-current triboelectric nanogenerator (DC-TENG) does not need to be rectified and is not restricted by a dielectric breakdown compared with an alternating current TENG (AC-TENG). Furthermore, the charge density of the DC-TENG reaches an ultrahigh level far beyond that of the AC-TENG based on a rational design. However, there are always some electrons remaining on the surface of the dielectric after the breakdown process in the DC-TENG, and therefore a low charge utilization is obtained. Herein, a simple and universal method is proposed through a double-layer structure design, that is, a triboelectric layer as the friction layer and an electret layer charged through a surface treatment as the field-enhancing layer to further improve the output performance of the DC-TENG, which is inspired by the fable “The Crow and the Pitcher.” Owing to the external field-enhancing breakdown effect, a double improvement in the breakdown efficiency and output charge density is obtained compared with a conventional DC-TENG. Moreover, a nearly constant output current has been demonstrated for directly powering electronics without a rectifier. This study provides a universal method for optimizing the output performance of a DC-TENG.