The Study On The Properties Of The BiFe_0.9Cr_0.1O₃ Solid Solution BiCrO₃/BiFeO₃ Bilayer Composite Films

In semiconductor photovoltaic materials,photons with energy higher than the band gap are absorbed to produce electron-hole pairs which are separated by the internal field in the p-n junction and collected with the electrodes.And semiconductor photovoltaic materials have exhibited their outstanding advantages such as mature technology and relatively high conversion efficiency.Consequently,the photo-induced voltage is limited by the energy barrier height in the interface region and usually smaller than the semiconductor band-gap.Therefore,the ferroelectric photo-voltaic effect has been attracted a great deal of attention due to its efficient polarization-governed mechanism of charge separation and ability to generate above band-gap voltages.Different from the traditional junction-based semiconductor photovoltaic effect,ferroelectric photovoltaic effect is generally thought that the internal electric field originates from ferroelectric polarization.Ferroelectric photovoltaic effect does not require an asymmetric interface and its photo-voltage is not limited by the band gap of the materials.Therefore,it can generate above band-gap voltage.So steady-state photo-current can exist in a homogeneous medium under uniform illumination,which is called bulk photovoltaic effect.However,the wide band-gap ferroelectric materials such as LiNbO₃,Ba TiO₃,Bi₄Ti₃O₁₂ can not effectively absorb visible light so that the intrinsic photovoltaic characteristics are unsatisfactory.Compared with conventional ferroelectric materials,the band-gap of BiFe O₃ materials is narrow,which eliminate photovoltaic response area in the near ultraviolet region.BiFeO₃ materials have a board development prospect in the practical application of photovoltaic effect.Special attention is paid to bismuth ferrite BiFe O₃,with rhombohedral perovskite structure,which is known to ferroelectric behavior at room temperature.Due to its unique properties,BiFeO₃ is a suitable material for plethora of possible applications,such as photocatalytic water splitting,smart sensing,spintronics and magnetic data storage.Periodically arranged narrow domains enable facile transport of generated charge across BiFeO₃,resulting in an output voltage exceeding that of a band-gap.BiFeO₃ is recognized as a potential material for photovoltaic applications due to its relatively narrow band-gap in comparison to other ferroelectric materials.Therefore,it is possible to obtain strong photovoltaic effect in near ultraviolet for BiFe O₃ films and it is necessary to further decrease the band-gap in order to regulate the photovoltaic response region from the near ultraviolet region towards visible region.So BiFeO₃ films?BiFe_0.9Cr_0.1O₃ solid solution films and BiCrO₃/BiFeO₃ bilayer composite films were prepared by using solution-gelation technique.Their structure,ferroelectricity,optical band-gap,photovoltaic spectral response and J-V performance were investigated systematically.It is shown that the enhanced ferroelectric properties are observed for BiFe_0.9Cr_0.1O₃ solid solution films and BiCrO₃/BiFeO₃bilayer composite films by interaction resulting between BiFeO₃ and BiCrO₃.The photovoltaic spectral responses of the normalized current for BiFe_0.9Cr_0.1O₃ solid solution films and BiCrO₃/BiFeO₃ bilayer composite films presents a noteworthy red-shift and moves towards the visible region so regulating their photovoltaic spectral responses compared with the pure BiFeO₃ films and the pure BiCrO₃ films.Thus photovoltaic response is attributed to the narrow band-gap of BiCrO₃/BiFe O₃bilayer composite films.The short circuit current density and open circuit voltage of BiCrO₃/BiFeO₃ bilayer composite films under illumination are much higher than the values for BiFe O₃ and BiCrO₃ films films.This study found that the method of forming solid solution and bilayer composite thin film with BiCrO₃ and BiFeO₃improved the ferroelectric and photovoltaic properties of BiFeO₃,extended the application range of ferroelectric thin film,and provided an idea for the research work of late-stage ferroelectric photovoltaic.