Research On Ferroelectric Photovoltaic Effect Of BiFeO₃ Based Thin Film

BiFeO₃?BFO?as a single-phase multi-iron material at room temperature,has a simple perovskite structure,in which the oxygen octahedron rotates around the body diagonal axis by a certain angle to form a rhombic deviation from the ideal perovskite structure structure.As a ferroelectric material,the open-circuit voltage of BiFeO₃ is not limited by the material forbidden band width,and its size is closely related to its bulk photovoltaic effect,showing a different mechanism from traditional p-n junction photovoltaic devices,due to its application in new optoelectronic device fields?such as solar cells?has become a hot spot in the academic field on the physics and applications of ferroelectric materials.However,when studying the photovoltaic effect of BFO thin films,it is found that the physical mechanism that causes this effect is often very complicated,such as the bulk photovoltaic effect that cannot be ignored when the film is thick,the domain wall of the complex domain structure in the film,and the Schottky junctions,depolarization fields caused by polarization,or structural defects within the film may all contribute to photovoltaics.BiFeO₃ material has higher residual polarization strength and lower band gap width?2.6-2.7eV?,high residual polarization strength means that the photovoltaic effect contributed by bulk photovoltaic effect and depolarization field is more significant,suitable band The gap width also allows it to effectively absorb visible and ultraviolet light,so it is a rare material for preparing photovoltaic devices,and the combination of BFO film and other materials can also improve photovoltaics.So this paper explored the photovoltaic effect of BiFeO₃-based photovoltaic devices through experiments,theory and modeling methods.The rhombohedral phase pure phase BiFeO₃ thin film of R3 C space group was prepared by sol-gel method,suitable process parameters were found,its transmittance was tested and analyzed,and its band gap width was obtained by extrapolation.The Cu₂O thin film was prepared by magnetron sputtering,and its optical and electrical properties were tested and analyzed to determine the best process parameters.The first-principles calculation based on density functional theory was used to study BiFeO₃ crystals.The selected exchange correlation potential was GGA-Perdew-BurkErnzerhof,the flat wave truncation energy value was 500 eV,and the geometric model was optimized to obtain the total state density,partial wave state density,energy band structure and optical properties of the BiFeO₃ crystal.The maximum value of the valence band was mainly concentrated in the O-5p state,and the minimum value of the conduction band was mainly concentrated in the Fe-3d state and the O-5p state.The maximum peak of Fe-3d state was mainly concentrated at-6.8 eV,and it hybridized with O-5p state here.The band gap of pure bismuth ferrite was 2.592 eV through the density of states and energy band structure.The peak of each optical property also coincided with the band structure,showing that the pure phase BiFeO₃ had better light absorption in the visible ultraviolet range.The photovoltaic effect of BiFeO₃-based photovoltaic devices was explored using the method of multiphysics modeling.In the sandwich structure device,the difference in work function of the upper and lower electrodes would cause the built-in electric field to strengthen to generate a larger open circuit voltage and short circuit photocurrent,and the combination of BFO film and Cu₂O film could make the short circuit photocurrent increase by an order of magnitude,greatly improving photovoltaic effect.