Synthesis And Photovoltaic Property Of BiFO₃ Thin Films

BiFeO3 (BFO) is the few known material that is both ferroelectric and antiferromagnetic at room temperature. The potential applications of BFO in memory devices, integrated circuits, transducer, spin electronics devices and other integrated ferroelectric devices, have led to an explosion of interest in its growth and properties. Besides, due to its small band gap and unique characteristics of polarization, BFO has overcame the constraints of the traditional solid-state solar cell band gap voltage, so that the ferroelectric thin film can perform the photovoltaic effect. The excellent optical and electrical properties of the BFO film exhibit its potential and applications such as solar cells and other optical device in the future.In this dissertation, BiFeO3 films were synthesized by sol-gel method, and La was doped to improve the properties of the films. The major work can be summarized as follows:(1) Bismuth nitrate and ferric nitrate were used as raw materials with acetic acid and ethylene glycol as solvent, the precursor of BiFeO3 thin films were prepared by strong stir at room temperature. Undopped and La doped BiFeO3 thin films were successfully deposited on Si, LNO and quartz substrates, respectively.(2) The X-Ray Diffraction was used to study the microstructure of the BiFeO3 thin films deposited on the different substrates and under different annealing temperature. The Scanning Electron Microscope was used to observe the surface and the cross-sectional of the films on Si and LNO substrates. The Atomic Force Microscope was used to research the surface of the BiFeO3 thin films with different amount of La doped.(3) The dielectric and ferroelectric properties of BiFeO3 thin films were studied. The optical properties were investigated via spectroscopic ellipsometry and transmission measurement. The optical constants and transmittance spectra of the BiFeO3 films are derived from these measurements. By these optical constants, we obtain the optical band gap was about 2.74eV. With the increase of La concentration, and the band gap Eg of films also changed.(4) The simple photovoltaic testing model had been set up, and the measurements were carried out. The open-circuit voltage was obtained from the tests of the BiFeO3 films, which were prepared in different conditions, such as on the different substrates, under different annealing temperature, with different amount of La doped and so on. The films on LNO substrate exhibited the relatively larger open voltage. As the increase of electrodes distance, the voltage value raised, and the dope of La could enlarge the open voltage.