| In recent decades,the consumption of non-renewable energy sources such as oil and natural gas has continued to increase,and energy problems have become increasingly prominent.To solve the problem of non-renewable energy consumption,renewable green energy such as wind energy,solar energy,and tidal energy have attracted more and more attention and research.As one of the most common energies in the natural environment,mechanical energy has the characteristics of wide frequency distribution,and most of it is a few hertz to several kilohertz of low-frequency energy,etc.,which can be collected and converted into electrical energy.However,the natural environment conditions are relatively changeable,and mechanical energy collection and conversion devices are required to be highly adaptable.At present,the life span of traditional electrochemical batteries is limited,which not only brings additional operations and costs for charging and battery replacement,but the excessive size of the battery limits the miniaturization of electronic devices.How to realize the network integration between devices into a micro-nano system has put forward a series of new requirements for the battery.With the development of the Internet of Things,nano-robots,micro-electromechanical systems,implantable biosensors,and various portable wearable electronic devices are in urgent need of independent,maintenance-free,and long-working energy supply systems.Therefore,how to achieve high-efficiency and long-life energy supply for devices and their systems has become a current research hotspot.A piezoelectric nanogenerator is an energy harvester that collects environmental mechanical energy and converts it into electrical energy.Because its piezoelectric effect is entirely based on the internal polarization of the material,it does not require a separate voltage source and magnetic field source.Piezoelectric nanogenerators do not need to be electrified in advance like electrostatic generators,nor do they have the bulky coil and magnet parts of electromagnetic generators,nor do they need to be in contact with another material like friction nanogenerators.Therefore,compared with other mechanical energy conversion technologies,piezoelectric generators have the characteristics of lightweight,durability,high-density power output,high sensitivity,and freedom from environmental factors such as humidity.Besides,the piezoelectric generator can be prepared in a small-sized structure and is easily integrated into a microelectromechanical system.At present,the main research bottleneck in the field of piezoelectric nanogenerators is how to improve their flexibility and achieve higher output,to adapt to more and more extensive application requirements.As a photoelectric material with excellent performance,cadmium sulfide is widely used in energy conversion and collection due to its low work function and excellent thermal stability.On the other hand,as a piezoelectric material with simple synthesis and high piezoelectric coefficient,it has great application potential in flexible piezoelectric nanogenerators and self-powered sensors.Therefore,this thesis is based on the theory and technical support of piezoelectric nanogenerator technology,to realize self-powered micro-nano devices and new sensors,and finally constructs a unique structure using new nanomaterials,which is a piezoelectric nanogenerator.A new attempt was made to construct and realize the self-powered micro-nano sensor.The main research contents and conclusions of this paper are as follows:(1)The neatly arranged and well-crystallized cadmium sulfide nanosheet arrays were prepared and synthesized by a template-free,gentle and simple hydrothermal synthesis method.X-ray diffraction shows that the nanosheets have a hexagonal wurtzite structure.Scanning electron microscopy and atomic force microscope images show that the synthesized nanosheets have a uniform and neat array structure with a thickness of about 100 nm.EDS energy spectrum measurement shows that the nanosheets only contain two elements,S and Cd,and the elements are evenly distributed on the entire surface of the nanosheets.(2)To realize the flexibility of the device,the nanosheet array layer is peeled off from the hard substrate through the mechanical peeling method;using the piezoelectric and semiconductor characteristics of the material,a high-sensitivity flexible piezoelectric nanogenerator is finally constructed.The working principle of the device was studied in detail;on this basis,the structure-activity relationship between the electric potential distribution in the cadmium sulfide nanosheet and the external force on the nanosheet was studied.Studies have shown that,in addition to the change in the piezoelectric potential distribution,the electrical generation process of the device is also related to the symmetrical Schottky contact when the metal is in contact with the semiconductor material and the change in the energy band structure.Using structural mechanics,electrical theory,and other theories to reach a calculation conclusion:when the magnitude of the external force stimulus is the same,the external force applied along the c-axis direction can make the nanosheet generate the largest piezoelectric potential,and the piezoelectric potential is proportional to the magnitude of the external force.This provides a theoretical basis for the structural construction of the device and the realization of the pressure sensing function.(3)The influence of different parameters on the electrical performance of the device is systematically studied.The device realizes effective energy collection and successfully provides the required electrical energy for driving digital watches and LED lights.At the same time,based on the flexibility and output characteristics of the device,it is used as a pressure sensor and a gesture sensor,and self-driving sensing can be realized without an additional external power supply.The experimental results show that the addition of the PET substrate significantly improves the output characteristics of the device.The increase in the size and frequency of the external force will also lead to an increase in output.Later,under the drive of a finger,the device can achieve a maximum open-circuit voltage of 1.2 V and a maximum short-circuit current of 6 n A.The output power density will vary with the external resistance,and can reach a maximum output power density of 6.13 n W/cm2 under a resistance load of 10 M?.In addition,application experiments show that the device can successfully charge the capacitor,and the energy conversion efficiency is as high as 3.6%.When using this device as a pressure sensor,the measurement range of 0.5-7.2 N can be achieved,and the sensitivity can reach 0.143 V·N-1.Finally,as a gesture sensor,the behavior of the finger can also be qualitatively analyzed by outputting images and voltage amplitude.Therefore,the piezoelectric nanogenerator made of piezoelectric materials with a three-dimensional structure in this paper not only provides a new method for environmental energy harvesting,but also a new attempt in the research and development process of self-powered sensing technology.There are many potential applications in the field of information sensing. |
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