Investigation On Heterogeneous Interface Construction And Photoelectric Effect Of BiFeO₃-based Ferroelectric Thin Films

Ferroelectric materials have attracted much attention in the fields of energy conversion,information storage,and electromagnetic shielding because of their spontaneous polarization that can be modulated by the direction of the applied electric field.In addition,some ferroelectric materials have narrow band gaps and can exhibit anomalous photovoltaic effects,and they also possess good mechanical and chemical stability,which makes them valuable for research in the field of optoelectronics.However,the optical band gap of ferroelectric materials still limits their ability to absorb sunlight,resulting in their ability to absorb only a very small fraction of the sunlight.In addition,the individual depolarization electric field(E_dp)has a limited effect on the separation and migration of photogenerated carriers,and these limitations make the performance of ferroelectric material-based optoelectronic devices difficult to meet current application requirements.Based on the conventional ferroelectric material bismuth ferrite（BFO）,this thesis focuses on improving the optoelectronic performance of ferroelectric materials by constructing heterogeneous interfaces through structural design and using interfacial effects to modulate the optoelectronic performance to obtain large carrier driving force and photocurrent density,and then investigates their photovoltaic performance and photodetection capability.The main research of this paper is as follows:A BFO/LSMO heterojunction with La_0.7Sr_0.3Mn O₃（LSMO）as the bottom electrode was prepared by the sol-gel method,and some of its basic structural properties as well as photovoltaic and photodetection performance were investigated.It was found that the short-circuit current density(J_sc)and the maximum open-circuit voltage(V_oc)of the heterojunction are 0.14 m A/cm² and 0.04 V,respectively,after electrode polarization.After photoelectric polarization,its J_sc and V_oc are increased to 1.2 m A/cm² and 0.04 V,respectively.In addition,with the best photovoltaic performance of the BFO/LSMO heterojunction,at which the heterojunction was able to obtain a maximum response rate of 18.6 m A/W and a detection rate of 11.7×10¹⁰ Jones under sunlight.Based on the previous BFO preparation process and the idea of constructing heterojunctions,Bi Fe_0.95Mn_0.05O₃/Bi_0.9La_0.1Fe O₃（BFMO/BLFO）heterojunctions with vertical structure were prepared on Si substrate by sol-gel method by doping BFO with two elements,La and Mn,respectively.It is found that after polarization at 90 V,the heterojunction achieves the best photovoltaic performance(J_sc=6.5 m A/cm²,V_oc=0.28 V),which is much larger than that of the monolayer films of BFO,BLFO,and BFMO.Further application of the BFMO/BLFO heterojunction to the self-powered photodetector demonstrated excellent photodetection performance,with a response rate of 0.477 A/W and a detection rate of 4.51×10¹² Jones under sunlight when the incident light intensity was 1m W/cm²;the response rates under 365,405,475,575,and 675 nm wavelength irradiation were 6.01,5.21,3.78,2.77,and 1.08 A/W,respectively;the corresponding detection rates were 5.68×10¹³,4.91×10¹³,3.57×10¹³,2.62×10¹³,and 1.02×10¹³ Jones,respectively.Based on the work in the previous part,a simple sol-gel method was successfully designed and used here to prepare a NiO/BFMO/BFLO as a light absorbing layer based on a BFMO/BLFO heterojunction and covering it with a NiO film as the top layer to promote UV light absorption.The UV self-propelled photodetector with NiO/BFMO/BFLO as the photoabsorption layer was prepared.The device can further improve the photocurrent density and achieve more accurate detection of UV light.The device is capable of detecting UV light at the weakest 0.1 m W/cm² light intensity,and the achieved response rate and detection rate are 17.668 A/W and 6×10¹³ Jones,respectively.