Preparation And Optimization Of ZnO-Based Flexible Piezoelectric Vibration Energy Harvester

As a widely used transparent oxide semiconductor material,ZnO(zinc oxide)has large band gap and exciton binding energy,high transmittance and superior piezoelectric property,which provides a new way of converting mechanical energy into electrical energy.The way has extremely important application prospect in energy acquisition and conversion.Therefore,the optimization of the piezoelectric thin film performance of the ZnO-based piezoelectric energy harvester and the improvement of the structure design of the multilayer film have become the hot topics for extensive research on improving the photoelectric performance and the output voltage of the piezoelectric energy harvester.In this paper,AZO thin films grown by DC magnetron sputtering were used as electrodes and ZnO piezoelectric films were grown by RF magnetron sputtering on opaque stainless steel substrates and transparent polymer substrates.Finally,multilayer piezoelectric energy acquisition sheets were prepared.The effects of sputtering parameters and annealing of piezoelectric films on the structure and properties of the films were investigated.The main contents and results are as follows:1.The parameter optimization of AZO thin films deposited on WG flexible transparent glass substrate was explored.The effects of thickness,sputtering power,working pressure,substrate temperature and pre-strain on the photoelectric properties of AZO thin films were investigated.The X-ray diffraction(XRD)pattern shows that the AZO films have prominent(0002)peaks,-indicating that the AZO films have a highly c-axis preferred wurtzite structure.It can be seen from the SEM surface and the cross-sectional view that the columnar structure of the AZO film is clearly and closely arranged.The optical test shows that all of the prepared AZO films have high light transmittance and about 80%transmittance in the visible range.The bandgap calculated from the absorption curve shows that the bandgap value of Al-doped ZnO becomes bigger.The resistivity of the AZO thin film is determined by the resistance and thickness.It found that the resistivity decreases rapidly as the deposition thickness increases firstly,and then after the thickness reaches a certain value(sputtering time 40 min),the resistivity increases as the thickness of the film further increases.The dependence of the resistivity of the AZO film on the sputter power is that the resistivity is minimized as the sputter power is increased to 100W and the resistivity is increased as the sputter power is further increased.The resistivity of the AZO film also changes as the working pressure changes,and the resistivity is minimized when the operating pressure reaches 0.9Pa.In addition,the resistivity of AZO thin films also decreases with the deposition temperature.Finally,the AZO film under pre-strain growth has a higher resistivity than the AZO film under normal growth and the least resistivity is at abase curvature radius of 13cm.2.The ZnO thin film was prepared by RF magnetron sputtering and the effect of sputtering parameters and post-processing on the properties of ZnO films was investigated.First of all,the properties of ZnO prepared on the opaque stainless steel flexible substrate were studied with the influence of annealing temperature.It can be found that the annealing treatment can effectively improve the crystalline quality and the forbidden band width.When annealed is at 100?and 150?,the grain size of ZnO thin films reaches the maximum,the crystallinity is the best and the band gap value is the largest.Then the effect of the ratio of oxygen to argon on the structure and properties of ZnO thin films grown on different polymer flexible substrates was studied.It can be found that the crystallinity of the ZnO thin film on the ITO/glass substrate is the best when the ratio of oxygen to argon is 0.3.The crystallinity of ZnO thin films on ITO/PEN and ITO/PET substrates becomes better with the increase of oxygen to argon ratio and reaches the maximum at 0.4,then the grain size has a slight decrease as the ratio of oxygen to argon continues to increase.All prepared ZnO thin films are uniformly arranged and the columnar structure of cross section is clearly visible.3.The multi-layer piezoelectric energy harvester with AZO/PMMA/ZnO/stainless steel and AZO/PMMA/ZnO/ITO/PET(PEN)was designed by optimizing the preparation parameters of AZO film and ZnO film.The work explores the output voltage characteristics of stainless steel-based energy harvesters as the annealing temperature and piezoelectric film thickness change.It can be seen that the output voltage of the energy harvesting plate is the largest at an annealing temperature of 150? and the output voltage reaches 234mV at an input vibration acceleration of 10 m/s2.In addition,the influence of piezoelectric thickness on the output voltage of energy harvester was also studied.It can be found that the output voltage of the harvester also increases with the increase of the thickness of piezoelectric thin film and has a linear increase.When the thickness of the piezoelectric film is increased to a certain value,the influence of the anneal of the ZnO film on the output voltage of the energy harvester will be weakened.Finally the thick ZnO film as the energy of the piezoelectric layer is prepared on the PET and PEN substrates.It can be clearly seen output voltage of energy harvester and the regular waveform.The flexible and transparent energy harvester has excellent performance and can be fully applied to self-powered energy harvesters and so on.