Mechanical And Photoelectric Energy Conversion And Self-Powered Sensors Based On Piezopotential

In recent years,the rapid development of sensor network has played a vital role in people's production and life.However,most of the existing sensors are powered by batteries.The traditional chemical batteries have a series of shortcomings,such as high-power consumption and environmental pollution,which limit the development of the sensors.Energy is widely distributed in the natural environment with a variety of manifestations.One of the ways to address the limitation of sensors is to design self-powered sensors that can work sustainably by collecting and utilizing the energy in the environment.Based on the physical basis of piezopotential,not only nanogenerators that collect different forms of mechanical energy in the environment can be fabricated,but also energy band structure of the P-N heterojunction interface can be adjusted by piezoelectric polarization,anticipating to enhance the photovoltaic performance of ferroelectric materials.Nevertheless,the output performance of piezoelectric nanogenerators is still to be improved and most of them contain toxic substances such as lead.Moreover,the use of piezopotential to regulate the performance of ferroelectric photovoltaics is still relatively rare.The thesis mainly attempts to prepare flexible piezoelectric nanogenerators with high output performance and self-powered mechanical sensors by virtue of piezoelectric theory.Another chapter is about the modulation of photovoltaic properties of BFO/ZnO heterojunctions with the aid of piezopotential by applying small strain to ZnO nanowires.The main research contents are as follows:?1?Chapter 3 introduces the fabrication of flexible piezoelectric nanogenerators with excellent performance and self-powered mechanical sensors.The piezocomposite films were made by the uniform mixture of organic polymers polydimethylsiloxane?PDMS?and 0.91K_0.48Na_0.52NbO₃-0.04Bi_0.5Na_0.5ZrO₃-0.05AgSbO₃-0.2%Fe₂O₃?KNN-BNZ-AS-Fe?piezoelectric ceramics with piezoelectric coefficient up to 500pC/N.Thereafter,a piezoelectric nanogenerator with the sandwiched structure of Cu/piezocomposites/Cu was constructed.By exploring the effects of different composite concentrations and ferroelectric polarization electric fields on the output of piezoelectric nanogenerators,the optimized output performance was obtained under a vertical force of 25 N at a frequency of 2 Hz.The maximum electric output is up to an open-circuit voltage of 52 V and a short-circuit current of 4.8?A.The KNN-BNZ-AS-Fe-based biocompatible piezoelectric nanogenerator can be used as a power source to successfully drive commercial light-emitting diodes?LEDs?without any storage unit.In addition,the piezoelectric nanogenerator could also potentially be utilized as a mechanical sensing counter and in collision alarm equipment due to a linear relationship between its output voltage and applied stress.This work provides a new direction for lead-free piezoelectric materials in the field of self-powered mechanical sensing,with potential applications in the fields of artificial intelligence,soft robots and biomedical devices.?2?In Chapter 4,the improvement of the photovoltaic property of the BFO/ZnO heterojunctions by the piezo-phototronic effect has been investigated.The proposed theory of piezo-phototronic effect has broadened the way to improve the photovoltaic property of ferroelectric thin films,but there is no literature report on the effect of piezopotential of piezoelectric semiconductor ZnO on the photovoltaic property of BFO/ZnO heterostructures.In this work,BFO films were prepared by a sol-gel method and ZnO thin seed layers with c-axis preferential growth were sputtered thereon by magnetron sputtering.Subsequently,uniform ZnO nanowire arrays were grown by hydrothermal method to construct BFO/ZnO heterojunction.Before small strain was applied,the photovoltaic performance of the BFO/ZnO heterojunctions is greatly improved compared to the photovoltaic output of the pure BFO films.That is,the open-circuit voltage and the short-circuit current are 1.5 times and 7 times larger than those of the pure BFO films without the formation of heterojunction.Meanwhile,the photoelectric response speed of the devices has improved to some extent.In addition,the photovoltaic performance of BFO/ZnO heterojunction placed on a microstress applied platform has been investigated with and without microstress.It is found that the photovoltaic effect of BFO/ZnO heterojunction can be enhanced by the piezopotential of ZnO nanowires.Based on the energy band,the regulation mechanism of piezopotential on photovoltaic effect of BFO/ZnO heterojunctions was briefly analyzed.This work will not only provide experimental support for exploring new type nanogenerator with synergetic effect of force and light,but also expand the application of piezophototronics in the field of ferroelectric thin films.