Study On Electrical And Photovoltaic Properties Of Double Perovskite Bi₂FeCrO₆ Thin Films

With the advancement of electronic information technology,traditional electronic devices have been unable to meet people's pursuit of micro-devices.There is growing interest in materials with special physicochemical properties,and some multifunctional materials have been proposed and studied.To address the coexistence of ferromagnetism and ferroelectricity at room temperature,the double perovskite oxide Bi₂Fe Cr O₆(BFCO)was proposed and attracted attention.Theoretical calculations show that BFCO has a ferroelectric polarization of 80?C/cm~2at room temperature.And the saturation magnetization is about 2?B/fu(about160 emu/cm~3).Furthermore,the dominant band gap(Eg)of BFCO is 2.4–2.6 e V,and the smallest Eg(i.e.,1.6 e V)can be obtained by optimizing the alternating order of Fe and Cr.Due to its various physical properties such as ferroelectricity,ferromagnetism,and photovoltaic properties at the same time,it indicates that BFCO has good potential reference value in the fields of storage,microelectronics,and photovoltaic devices.Since BFCO was proposed,researchers have successfully grown epitaxial BFCO films on substrates with different orientations,and studied their physical properties such as structure,ferroelectricity and ferromagnetism.Simple devices were fabricated by epitaxial BFCO thin films,and applications including photovoltaics,photocatalysis,and photodiodes were realized.It is worth noting that the current research on BFCO is mostly focused on epitaxially grown thin films,while the high-cost growth and preparation methods such as magnetron sputtering and pulsed laser deposition limit the application of BFCO thin films.In view of this background,in this thesis,BFCO thin films were prepared by sol-gel method with simple preparation steps and low cost,and the preparation process was explored.Effect and other material properties,and in-depth discussion and analysis of the relationship between the properties and structure of BFCO thin films.The specific work content is as follows:First,we prepared BFCO films by the sol-gel method and optimized the fabrication process of the films.The morphology and structure of BFCO films annealed at different temperatures were analyzed.The results show that as the annealing temperature increases,the crystallinity of the films is better and the average size of the BFCO grains(possibly composed of multiple crystallites)increases with the increase of the annealing temperature.Among them,the BFCO films prepared by annealing at 700°C have good crystallinity and smooth and dense surface morphology.Furthermore,the X-ray diffraction(XRD)results of the BFCO thin films show that the thin films have polycrystalline properties with random orientations.Secondly,the resistive switching properties of BFCO films were tested.Resistive switching phenomena with different properties were observed in the Au/BFCO/FTO structure composed of BFCO films annealed at different temperatures.The RS behavior of the device and the change of resistive switching performance due to annealing temperature are analyzed and discussed.The results show that the resistive switching behavior is the result of the interaction between the interfacial barrier and oxygen vacancies,and the change of RRAM performance caused by annealing temperature is attributed to the crystallinity and oxygen vacancy defect content.When annealed at 700°C,the films obtained the largest and most stable switching ratios.These findings will aid in the design and fabrication of resistive switching memory devices.The photoinduced negative differential resistance(NDR)and carrier transport mechanism of BFCO films were then investigated.Au/BFCO/FTO devices were fabricated by sol-gel method at 700°C annealing,and optical modulation switching RS behavior and photoinduced negative differential resistance effects were found in Au/BFCO/FTO devices.In addition,the mechanism of RS behavior,NDR effect,and photoinduced carrier dynamics of Au/BFCO/FTO devices are discussed,and the formation of oxygen vacancies is proposed to explain the good and stable RS performance,and the efficient separation of photogenerated carriers can lead to NDR effect,which is further confirmed by transient absorption spectroscopy.The conversion between RS memory and NDR effect has potential applications in light modulation,multifunctional electronic devices,electronic information,and optical quantum computers.Finally,the photovoltaic performance test was carried out.Devices on different substrates of Au/BFCO/FTO,Au/BFCO/LNO/Si and Au/BFCO/LSMO/Si were fabricated by sol-gel method,and obvious photovoltaic effect was found.The photovoltaic effect results illustrate the great potential of BFCO thin films in photovoltaic devices,which may contribute to the development of high-efficiency,low-cost,and low-weight solar cells.In conclusion,BFCO polycrystalline thin films were prepared by sol-gel method,which showed excellent performance in resistive switching,photo-induced negative differential resistance and photovoltaic effect.These findings have positive implications for the design and fabrication of new multifunctional electronic devices from BFCO thin films.