BiFeO₃-based Polarization Devices And Their Sensing Application Based On Piezoelectric Potential

With the rapid development of the Internet of Things in recent years,portable electronic devices have been comprehensively deployed in every fields.The microelectronic devices that make up the Internet of Things all require micro-energy to supply power.Generally,chemical batteries with limited life and environmental hazard are used,and management and recycling of the batteries are also an urgent problem to be solved.Piezoelectric nanogenerator(PENG)proposed by Zhong Lin Wang In 2006,has the characteristics of being able to convert the mechanical energy in the environment into electrical energy,whose merits are independent of time and place,good environmental applicability as well.Therefore,the PENG is particularly suitable for solving the power supply problem of microelectronic devices in the Internet of Things,and provides a new solution for the development of self-powered sensors.In addition,there is an urgent need to expand the application scenarios of PENG in order to broaden the application range of PENG in the Internet of Things.In 2010,Zhong Lin Wang discovered and proposed the piezo-phototronic effect.The piezo-phototronic effect mainly uses the piezopotential to adjust the energy band structure at the interface,so as to effectively regulate the carrier transport at the interface to achieve a new type of self-powered optoelectronic device with high performance and high sensitivity.Piezo-phototronic effect has made a significant impact in the fields of sensors,MEMS and artificial intelligence.More importantly,it has been reported that traditional research fields such as solar cells,light emitting diodes,artificial interaction,and ferroelectric photovoltaics can also be combined with piezo-phototronic effect to design electronic devices with outstanding performance and distinctive characteristics.Therefore,the two research fields of PENG and piezoelectric optoelectronics based on piezoelectric potential will play an important role in the future development of the Internet of Things.This thesis successfully enhanced the output performance of the PENG by virtue of the interconnected 3D porous structure and rational doping of the piezoelectric fillers,and the photoelectric performance of BLFO/ZnO heterojunction is boosted by piezo-phototronic effect and ferroelectric polarization.The main research contents are as follows:(1)In this thesis,we have succeeded to improve the piezoelectric properties of BFO and the higher stress transferability of porous piezoelectric ceramics to prepared PENG with better performance.The optimized interconnected 3D porous skeleton effectively conquers the main problems of current piezocomposite film based on particles in terms of lower stress transferability and particle aggregation.The enhanced stress transferability of the interconnected 3D porous skeleton was further proved by the COMSOL multiphysics software as well as the experimental results.The best open-circuit voltage(VOC)and short-circuit current(ISC)are 16 V and 2.8 ?A,respectively.Which 5.3 and 5.6 times higher than those of conventional PENG derived from undoped BFO without 3D structure.Therefore,this PENG can efficiently recycle and store tiny mechanical energy through a simple rectifier circuit.In addition,the self-powered mechanosensation system is designed by using the piezoelectric signal as the trigger signal,which has been applied as demonstrations in fire extinguishers and household applies.We believe this work builds a green pathway that exploits highperformance flexible PENG,and will further inspire the rapid progress of PENG toward practical applications of mechanosensation system.(2)In chapter 4,the photoelectric performance of BLFO/ZnO heterojunction boosted by applying external strain and electric field has been investigated by utilizing piezo-phototronic effect and ferroelectric polarization.The VOC and short-circuit current density(JSC)of the BLFO/ZnO heterojunction increased from 0.379 V and 0.271 m A /cm2 at 0 strain,finally to 0.411 V and 0.419 m A/cm2 at-2.3% compressive strain and +10 V pulse voltage,which is about 8.4% and 54.6% higher than the test results at 0 strain.In order to explain the reasons for the enhanced photoelectric performance of the BLFO/ZnO heterojunction under strain and forward electric field polarization conditions,we carefully analyzed the band diagram of the BLFO / ZnO heterojunction and proposed a reasonable and feasible explanation.In addition,simulation of piezopotential of the ZnO nanowires array and BLFO/ZnO heterojunction energy band structure was performed by COMSOL simulations.The experimental results are consistent with the simulation calculations.This work not only provides a new way to enhance the photoelectric response of ferroelectric semiconductor heterojunctions but also expands the research field of polarization electronics devices...