Influence Of Carrier Transport Layers And Resistive Switching On Photovoltaic Performance Of Bismuth Ferrite Thin Films

Ferroelectric materials exhibit reversible spontaneous polarization at room temperature with potential applications in future multi-functional calculations,data storage,photodetector,photocatalysis,and photovoltaic.BiFeO₃ as the only single-phase multiferroic material with both antiferromagnetic and ferroelectric properties at room temperature has attracted broad attention of researchers for many years.Among many perovskite ferroelectric materials,BiFeO₃ has a relatively narrow band gap value of 2.67 eV,making it more advantageous in the field of ferroelectric photovoltaics.The A or B-site chemical substitution and the AB-site co-substitution of BiFeO₃ have a very flexible adjustment effect on ferroelectric,ferromagnetic and photoelectric properties.The unique narrow band gap and ferroelectric domain wall structure of BiFeO₃ make its open-circuit voltage far beyond the band gap value.In the future photovoltaic field,BiFeO₃ and its chemically modified materials occupy an important position.In this paper,the sol-gel method combined with pulsed laser deposition technique was used to fabricate the pure phase BiFeO₃ film and A-site Gd-doped multilayer film for the photovoltaic researches.The mismatch between band structures of a light-absorptive layer and hole or electron transport layers will significantly deteriorate the performance of photovoltaic devices,which is generally alleviated by inserting a mitigating layer.In this report,we propose an alternative strategy to improve the efficiency by using resistive switching,which may decrease defect density in bulk and the lower barrier height at the interface due to the migration of defects to the interface under a certain electric field.By using a BiFeO₃ film as a model light harvesting layer,a TiO₂ mesoporous layer as an electron transport layer,and NiO_x as a hole transport layer,bipolar resistive switching behavior has been observed.By setting the device in the low resistance state under certain applied voltages,performance has been significantly improved.Compared with the virgin device,the highest short-circuit current J_sc increases 2.3 times from2.38?A cm^-22 to 5.66?A cm^-2 and open-circuit voltage V_oc increases 1.35 times from 0.39 V to0.525 V.In the second part,we performed A-site chemical modification of BiFeO₃ by Gd doping with concentration of 0,1%,3%,5%.The mesoporous TiO₂ and NiO_x films were also used as the electron transport layer and hole transport layer,respectively.Chemically modified BiFeO₃ has better structural stability and smaller optical band gap value.The J_sc of 5%Gd-doped BiFeO₃ increased by 3.46 times to 20.85?A cm^-2,compared with pure phase BiFeO₃ film under one solar illumination condition.