Research On Photoelectric Properties And Application Of Bismuth Titanate Ferroelectric Material

Ferroelectric materials have been widely used in ultrasonic transducers,infrared optoelectronic detection,memory and other fields due to their piezoelectric,ferroelectric,thermoelectric and other characteristics.In recent years,ferroelectric thin films have been proved to have special photovoltaic effect,which has aroused great interest of scientific researchers.However,most ferroelectric materials have wide bandgap and low conductivity.So far,the photocurrent produced by ferroelectric thin films has generally been very small.Based on this background,Bi₄Ti₃O₁₂ thin film was selected as the research object.The purpose of further optimizing the photoelectric effect characteristics was to study the effects and mechanism analysis of composite films and element doping on their optical properties and band structure.In this paper,the microstructure,ferroelectric and photoelectric properties of Bi₄Ti₃O₁₂/TiO₂ bilayer,La doped Bi₄Ti₃O₁₂ ferroelectric thin film,and Bi_3.25La_0.75Ti₃O₁₂/TiO₂ bilayer were studied by using sol-gel method.The main research results are as follows:Firstly,the preparation of Bi₄Ti₃O₁₂ ferroelectric thin films by sol-gel method was studied.On this basis,the Bi₄Ti₃O₁₂/TiO₂ double layer film was successfully prepared,and related characterization and performance tests were conducted.The results showed that the photoelectric response of Bi₄Ti₃O₁₂/TiO₂ composite bilayer was much more obvious than that of TiO₂ or Bi₄Ti₃O₁₂ films alone,and B₄T₄(B stands for Bi₄Ti₃O₁₂ film,T stands for TiO₂ film,and 4 stands for the number of coating layers)bilayer had the best photoelectric response.In addition,we investigated the effects of bias and polarization on the photoelectric response characteristics of B₄T₄ composite double-layer thin films as well.Under the condition of positive bias,the photocurrent density of B₄T₄ bilayer increased.In contrast,the current density decreases under negative voltage conditions.The J-T characteristic of the B₄T₄ composite bilayer with positive polarization is not as good as that with non-polarization.After negative polarization of-2v voltage,the photovoltaic effect is significantly enhanced,and the current density and open circuit voltage are correspondingly increased.After the positive polarization of 2V,the direction of photocurrent reverses and the density of photocurrent decreases.Secondly,La doped Bi₄Ti₃O₁₂ ferroelectric thin films were prepared by sol-gel method to study the effects of different La doped amounts on the microstructure,ferroelectric properties and photoelectric properties of Bi₄Ti₃O₁₂ ferroelectric thin films.No hetero facies appeared in all the film components,and with the increase of the doping amount of La element,the diffraction peak gradually moved to a higher angle,the grain size gradually decreased,the absorption edge shifted blue,and the band gap width slightly increased.The influence of different doping amount of La on the photoelectric response of Bi₄Ti₃O₁₂ thin film was studied by J-T and J-V test.The results showed that the photoelectric response of Bi₄Ti₃O₁₂ films doped with La element was better than that of Bi₄Ti₃O₁₂.Finally,the Bi_2.25La_0.75Ti₃O₁₂/TiO₂ bilayer was prepared by sol-gel method.The prepared films were characterized by XRD,SEM and UV-vis,and their photoelectric properties were investigated.The photoelectric response of Bi_2.25La_0.75Ti₃O₁₂/TiO₂bilayer was much stronger than that of TiO₂ alone or Bi_2.25La_0.75Ti₃O₁₂.In addition,we also studied the effect of different top electrodes on the photoelectric response of Bi_2.25La_0.75Ti₃O₁₂/TiO₂ composite film.We tested the J-T curve of Au/BL₄T₄/FTO and Ag/BL₄T₄/FTO devices under simulated sunlight?AM1.5?,and found that the photoelectric response of the two devices was different.This is because the work function of the top electrode is different,and the internal electric field generated between the thin film and the electrode causes that the photovoltaic effect of Ag/BL₄T₄/FTO device under white light irradiation is lower than that of Au/BL₄T₄/FTO device.