Investigation On Fabrication Process And Photovoltaic Effect Of BFO-based Ferroelectric Thin Film

As a clean renewable energy source,solar energy will solve the problems of environmental pollution and resource shortage if it can be effectively utilized.Therefore,the development of photovoltaic materials has become a hot research topic.Ferroelectric photovoltaic materials have broad application prospects in the photovoltaic field due to their narrow band gap,low cost,better carrier transfer,and high stability of chemical and thermal.The separation of photoexcited carriers in the ferroelectric photovoltaic effect is driven by ferroelectric polarization.Moreover,the output photovoltage is much large than the band gap of the crystal.Among the ferroelectrics,BiFeO₃?BFO?has a large remnant polarization and relatively small band gap?2.7 eV?,exhibiting the potential application in the field of ferroelectric photovoltaic.In this paper,the photovoltaic properties of B site-doped BFO-based ferroelectric thin films were prepared,and the ferroelectric properties,optical properties,dielectric properties,leakage properties and photovoltaic properties of the fabricated Bi₂FeMo_xNi_1-xO₆?BFMNO?films were investigated.This paper mainly focuses on the following problems:?1?Ferroelectric Bi₂FeMo_xNi_1-xO₆?BFMNO?thin films were fabricated using the sol-gel method.The thin films have a broad-band absorption in visible light range of400-650 nm.With the increase of Mo content,the optical bandgap decreases from 2.19 to2.07 eV.More importantly,the as-prepared BFMNO thin films have self-polarization behavior that causes the forming of the depolarization field(E_dp)and build-in field(E_bi)in the thin films.The narrow band gap and strong ferroelectric self-polarization play a crucial part in improving the photovoltaic effect.The thin film of x=0.7 has the optimum open circuit voltage(V_oc)and short circuit current(J_sc)which are 5.41 V and 71.07?A/cm²under light illumination of 110 mW/cm².In addition,the photovoltaic effect of the thin film also exhibits a good adaptability in high temperature environment.This work highlights the applications of the BFMNO thin films as a novel high-performance ferroelectric photovoltaic material.?2?Based on the determination of the above optimal components.Bi₂FeMo_0.7Ni_0.3O₆ferroelectric thin films of different thicknesses?570,640,700,770 nm?with vertical structure?Au/BFMNO/Pt?were prepared on the Pt substrate by sol-gel method.Here,we propose an approach to improve the PV properties of thin films,achieving high PV properties by tuning the thickness of film.The ferroelectric Bi₂FeMo_0.7Ni_0.3O₆ thin films of different thickness prepared by the sol-gel process are investigated.It is found that the short circuit current first increases and then decreases with increasing film thickness.The700 nm film exhibits the highest J_scc and optimum V_occ which are 0.09 mA/cm² and 0.38 V under light illumination of 110 mW/cm².It is demonstrated that the further improvements of the PV properties are attributed to the tunable favorable bandgap?<2 eV?,high absorption and strong self-polarization caused by the tuning of thickness.Furthermore,our research demonstrates that the main driving force of separating and transporting photoexcited carriers is the E_dp,whereas the E_bii at the interface plays a weak role.?3?A Bi₂FeMo_0.7Ni_0.3O₆ flexible ferroelectric thin film with asymmetric vertical structure?Au/BFMNO/LNO/Ni?was prepared on a flexible nickel foil substrate by sol-gel method.The effect of stress on the photovoltaic performance of the film was investigated.The photovoltaic properties of the films bent under different curvatures have slight variations.With the decrease of the bending radius?15-5mm?,the V_occ is about 0.7 V,and the J_scc is decreased from 8.02 to 4.05?A/cm²,which may be due to the stress affecting the polarization of the ferroelectric material.The prepared Bi₂FeMo_0.7Ni_0.3O₆ flexible ferroelectric thin film has excellent mechanical stability,and the change of photovoltaic performance is small under multiple cycles of bending.The photocurrent direction of the flexible ferroelectric thin film can be converted with the change of the polarization direction.This unique feature broadens the application field of ferroelectric photovoltaic materials.