The Study On Photocurrent And Electrical Microstructure Of Bi_0.5Na_0.5TiO₃-Based Ferroelectric Semiconductor Ceramics

The increasingly serious energy shortage and environmental deterioration promote the research and utilization of new energy by researchers.In the current situation of energy crisis,photovoltaic technology and industry have been rapidly developed.Up to now,traditional single P-N junction solar cells have dominated the solar cell industry for decades due to their mature technology and relatively high power conversion efficiency（PCE）.However,their PCE is below the Shockley-Queisser limit（33.7%）because the maximum optical voltage is limited by the band gap.Therefore,the development of new photovoltaic materials has attracted much attention.Fortunately,the ferroelectric photovoltaic（FEPV）effects observed in perovskite-type materials are of great interest to researchers due to their good stability and easy availability of raw materials in solar cells.Among all ferroelectric perovskite oxides,Bi_0.5Na_0.5Ti O₃（BNT）derived materials have been widely concerned.As an environment-friendly ferroelectric material,BNT has a high Curie temperature（Tc）of～320°C and a large residual polarization（P_r）of～38μC/cm².The large spontaneous polarization of BNT makes its photovoltaic applications possible because the photoexcited carriers can be separated effectively under the action of the internal polarization field generated by the spontaneous polarization of ferroelectric materials.However,the band gap value of pure BNT is greater than 3.1e V,so the light absorption is mainly in the deep ultraviolet（UV）region,which limits its development in the photovoltaic field.The traditional perovskite is ABO₃.In recent years,A lot of work has been done to optimize the ferroelectric and piezoelectric properties of BNT materials.Bi_0.5Na_0.5Ti O₃-Ni Ti O_3-δ、Bi_0.5Na_0.5Ti O₃-Sr Fe O_3-δ、Bi_0.5Na_0.5Ti O₃-Sr Mn O_3-δ、Bi_0.5Na_0.5Ti O₃-Mg Co O_3-δhave been successfully prepared by replacing the A and B sites of the perovskite in ABO₃.This doping method can effectively reduce the band gap of pure BNT and expand the light absorption range of BNT.However,there are few studies on the photovoltaic effect of this system.Based on this,perovskite oxide Bi_0.5Na_0.5Ti O₃with ABO3 type was selected.The main system of our research is shown:（1-x）Na_0.5Bi_0.5Ti O₃–x Ba Co_0.5Nb_0.5O_3-δ（BNT–BCN;x=0.00、0.05、0.10、0.15、0.20）、（1-x）Na_0.5Bi_0.5Ti O₃-x Ba Ni_0.5Nb_0.5O_3-δ（BNT–BNN;x=0.00、0.05、0.10、0.15、0.20）、（1-x）Na_0.5Bi_0.5Ti O₃-x Ba Zn_0.5Nb_0.5O_3-δ（BNT–BZN;x=0.00、0.05、0.10、0.15、0.20）、（1-x）Na_0.5Bi_0.5Ti O₃-x Ba Fe O_3-δ（BNT–BF;x=0.00、0.20、0.05、0.70、0.10）ferroelectric semiconductor ceramics.Transition metal ions were doped at A and B sites by ion doping,and then ceramic samples were prepared by traditional solid-state sintering process.By testing the samples,the optical band gap of ferroelectric semiconductor ceramics is reduced to a certain extent,and the phase structure,microstructure,lattice vibration,optical properties,ferroelectric properties and impedance are studied in depth.Through the analysis of the results,it is found that BNT based materials have high photovoltaic effect.These results provide a reference value for our further research on the photovoltaic effect of Perovskite Ferroelectric semiconductor,and are expected to be applied in reality in the future to solve the current energy shortage problem.