Preparation Of Barium Ferrite Thin Films And Study On Ferroelectric Photovoltaic Properties

In addition to its various functional properties such as polarizability,piezoelectricity,pyroelectricity,ferromagnetic and dielectric properties,BiFeO3 is also a narrow bandgap ferroelectric material which exhibits unique coupling properties of ferroelectric polarization and light-induced effects.This provides a novel way to develop efficient and stable photovoltaic devices in the future.Nd-doped BiFeO3 films,Cr-doped BiFeO3 films and Nd-Cr co-doped BiFeO3 films were successfully fabricated on FTO glass substrate via sol-gel and spin-coating methods.The main conclusions are as follows:1.By testing the UV-Vis absorption spectrum,it was found that the three forms of doping all increase the light absorption rate of film.The optical band gaps of pristine BiFeO3,Bi0.9Nd0.1FeO3,BiFe0.89Cr0.11O3 and Bi0.9Nd0.1Fe0.89Cr0.11O3 thin films are 2.40,2.22,2.30 and 2.18 eV respectively,indicating that element doping can reduce the optical band gap of BiFeO3 film.The reduced bandgap facilitates the transport of carriers.2.With Nd doping,Cr doping and Nd-Cr co-doping,the leakage current of the film is also effectively reduced.Compared with all samples in this subject and element doped BiFeO3 films in the references,the Bi0.9Nd0.1Fe0.899Cr0.11O3 film exhibits the lowest leakage current density,which is three to four orders of magnitude lower than the leakage current density of the pristine BiFeO3 film.The decrease of leakage current also enhances the ferroelectric polarization and dielectric property of the film.The enhancement of ferroelectric polarization is more favorable for the separation of photogenerated carriers,and the enhancement of dielectric property can improve the ability of the film to store charges.3.Both the short circuit photocurrent density and the open circuit photovoltage of these three types of doped BiFeO3 film are clearly improved compared with the pristine BiFeO3 film.The power conversion efficiencis of Bi0.9Nd0.1FeO3,BiFe0.899Cr0.11OO3 and Bi0.9Nd0.1Fe0.89Cr0.11O3 films are about 12 times,4 times and 35 times respectively as the power conversion efficiency of pristine BiFeO3 film,which proves that the effect of Nd-Cr co-doping is the best.The enhanced photovoltaic property benefits from the enhancement of light absorption,the reductions of band gap and leakage current and the increase of ferroelectric polarization intensity after element doping.The element-doped BiFeO3 film exhibits improvements in various properties,which favored the practical application of BiFeO3 in multifunctional devices such as nonvolatile ferroelectric memories,novel photovoltaic devices and high frequency electrical components.