| With the rapid development of human society,more and more distributed mobile electronics are widely used in daily life and industrial production.However,the working time of electronic depends entirely on the capacity of batteries,so it has become an impossible task to replace batteries regularly.And,how to treat a large number of replaced wasted batteries harmlessly will be a difficult problem that puzzles the development of the environment.The invention of piezoelectric nanogenerator（PENG）provides an opportunity to solve the problem of continuous and stable power supply for electronics.PENGs can convert discrete and irregular mechanical energy in the environment into electrical energy,which can continuously supply power to electronics for a long time after circuit management and storage,effectively avoids a series of problems such as replacement and maintenance of traditional batteries.Nevertheless,the low output of PENGs has been hindering their practical application.Major factors affecting the output of a PENG include the piezoelectricity of the piezoelectric module,the size and structure of the device,and driving force.In this thesis,we try to improve the output of PENG by improving the piezoelectricity of piezoelectric module and constructing a novel structure,and develop a self-powered ultraviolet sensor based on high output PENG.（1）The piezoelectricity of polyvinylidene difluoride（PVDF）is improved by the second phase addition of ZnO nanowires with high crystallinity and high specific surface area combined with electrospinning preparation technology.Compared with PVDF powder whose main crystalline phase isαnon-piezoelectric phase,the crystallinity andβpiezoelectric phase content of PVDF nanofiber are increased to 46.5%and 74.8%respectively.Adding 3 wt%ZnO nanowires,the output of the PENG is increased to 1.9 times that of pure PVDF nanogenerator,which effectively improves the output performance of PVDF piezoelectric nanogenerator.（2）The piezoelectricity of PZT-epoxy film is improved by introducing dielectrophoresis（DEP）to enhance the connectivity of PZT particles in PZT-epoxy composite film.The transmission channel of external force in PZT-epoxy film is also optimized by optimizing epoxy matrix Young’s modulus,so as to further improve the output of PENG.After DEP,the output current and voltage of PENG based on PZT-epoxy film are increased by 8 times and 3.3 times respectively;When the Young’s modulus of epoxy matrix increases from 1.4 MPa to 2420 MPa,the output current and voltage of PENG are also enhanced by 8 times and 7 times respectively.The maximum output current density and transferred charge of PENG based on the optimized PZT-epoxy film reaches 126μA cm-2 and 21.5 n C cm-2,respectively,which dramatically improved the output current density of PENG.Furthermore,a PENG with three-dimensional interdigital electrode structure based on PZT-epoxy film is constructed,the output current is greatly enhanced by introducing more polar interfaces,and the harvesting efficiency of mechanical energy increases synchronously.Under a driving pressure of 0.53 MPa,the output current of the PENG reaches 344μA,the corresponding current density and transferred charge density reaches 205μA cm-2 and1125μC cm-2,respectively.（3）A novel 3D spirally coiled piezoelectric nanogenerator（SC-PENG）is designed and developed,which reduces the stress concentration of the PZT-epoxy film by converting uneven axial large impact pressure into a more uniform radial pressure,thereby achieving the efficient harvesting of mechanical energy with large impact pressure in a wide range of 80 k Pa～6.32 MPa.Moreover,the harvesting efficiency of mechanical energy is improved by constructing an alternating spiral coiled double piezoelectric layer.Under an impact pressure of 3.05 MPa,the output current,voltage and transferred charge density of the SC-PENG reaches 196μA,36 V and 2550μC cm-2,respectively.The transferred charge density is 1.5 times that of PENG’s record.（4）A novel integrated self-powered ultraviolet sensor is developed by coupling barium titanate（BTO）piezoelectric effect and ferroelectric photovoltaic effect,which is based on BTO nanofiber membrane to improve the PENG output performance.The self-powered sensor can detect 365 nm ultraviolet light in the light intensity range of20μW cm-2 to 10 m W cm-2,and the response and recovery time of the sensor are 4.7 s and 3.7 s respectively,showing a quick response and recovery process.The response range of the sensor includes the calibration range(0.5 m W cm-2 to 2.5 m W cm-2)of ultraviolet light intensity level in the existing meteorological industry,which shows the broad practical prospect of BTO nanofiber-based integrated self-powered ultraviolet sensor. |
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