Preparation And Photoelectric Properties Of BiFeO₃/FTO Thin Film Materials

The photoelectron chemical ultraviolet detector is a self-powered photodetector.It has the advantages of low cost,simple structure,working at room temperature,and stable working state.The detector consists of three parts,of which the photoanode is one of the most important components that determine the performance of the device.The semiconductor material on the surface of the photoanode plays the role of separating photogenerated carriers,inhibiting the recombination of carriers,and transporting photoelectrons to the external circuit.Therefore,the choice of photoanode material is very important.Bi Fe O₃（BFO）is a ferroelectric material that also has ferroelectric properties at room temperature.The self-polarization field and depolarization field generated have a positive effect on the migration of photogenerated electrons.In addition,BFO is a direct band gap semiconductor with a narrow band gap of only 2.67 e V.These properties are all conducive to its use as a photoanode material for the detector.However,BFO itself has some shortcomings.First of all,its leakage current is relatively large,which may not be conducive to the migration of electrons and may cause recombination.In this regard,we consider using a coating method to coat BFO with a layer of Sn O₂ to form a heterojunction to improve the performance of BFO.In this paper,a hydrothermal synthesis method is used to generate BFO films on FTO substrates,and to characterize them.The influence of preparation methods on the morphology and structure of the films is studied,and suitable reaction parameters are found to prepare BFO films.We studied the optical properties of the film,discussed its absorbance and absorption spectrum,tried to use the tauc-plot method to calculate the optical band gap of the BFO,and then,we used PFM and ferroelectric instrument,in the micro and macro perspectives Observed and proved the existence of BFO ferroelectricity.After that,we also used the hydrothermal synthesis method to prepare the Sn O₂ coating film,and used XRD and SEM to characterize the phase structure and morphology of the Sn O₂ coating.After preparing the photoelectrochemical ultraviolet detector using it as a photoanode material,the photoelectric performance of the device was studied,focusing on the on-off ratio and corresponding time of the detector.After being coated with Sn O₂,the switching ratio of the device has increased from 19,000 to 42,000,which is an increase of 221%compared with the uncoated BFO film;the corresponding time has been shortened from the previous51 ms to 30 ms,and the performance has increased by 60%year-on-year.It has been proved that Sn O₂ coated on BFO film can significantly improve the detection performance of UV detectors.Except for the first time,in other tests,Sn O₂ coated devices have greatly improved on many key parameters such as open circuit voltage,short circuit current density,and voltage attenuation curve.Through theoretical simulation,we know that the performance improvement is theoretically mainly due to the heterojunction formed between Sn O₂ and BFO,which promotes the separation of photogenerated carriers and effectively inhibits recombination.At the same time,the energy level of Sn O₂is just at the BFO level.Between the energy level and the LUMO energy level of the dye molecule,it acts as an energy level ladder,making it easier for photogenerated electrons to enter the external circuit from the dye through the photoanode.Through theoretical and practical tests,we have successfully obtained the help of Sn O₂ coating on the performance of BFO-based photoelectrochemical ultraviolet detectors,which proves that Sn O₂ coating can indeed play the role hoped in the beginning of this topic.