Optoelectronic-Ferroelectric Properties Of Halide Perovskite

Many interesting applications of halide perovskites have come to light recently.Although halide perovskites have been mainly used for photovoltaics over the past five years,these materials have unique features that are remarkably advantageous for various other applications.Here,we introduce a broad range of halide perovskite-related applications,such as solar cells,memristor,piezoelectric generators.,electrostrictive effect.There are increasing concerns over some reports that the hysteresis is plausibly an intrinsic property of perovskite materials,even originates from the ferroelectricity of the halide perovskite.As mentioned above,several ferroelectric oxide perovskites such as BaTiO₃,BiFeO₃,etc.,were discovered to manifest photovoltaic effect since the 1950s.The studies on ferroelectrics reveal that the steady-state photocurrent and output voltage can be achieved in the ferroelectric homogeneous bulk having intrinsic non-centrosymmetry.A recent mechanism is proposed that the nanoscale domain walls of ferroelectric possessing built-in electric field are in the function of separating photogenerated excitons.For the conventional semiconductor photovoltaic devices,the separation of the charge carriers normally happens at p-n junctions.And the size of junction is almost on the order of micrometers.The separated charge carriers must diffuse through the junction to reach their respective electrodes,whereas they may be more likely to encounter one another and recombine during the diffusion process.For ferroelectrics,however,the probability of carrier recombination within a domain will be reduced because of the smaller size of ferroelectric domains which are on the nanometer scale depending on the cage of the perovskites.In this regard,the ferroelectric domain mechanism is essentially different from the photovoltaic effect of traditional semiconductor junction.Thus,ferroelectricity is considered to be a origin of the outstanding photovoltaic behavior of the halide perovskite.The introduction in the first chapter of this paper outlines the basic structure,development process and research status of halide perovskite.It also introduces applications related to halide perovskites,such as solar cells,resistance switch memories,piezoelectric generators,and electrostrictive responses.In Chapter two,we report an excellent ferroelectricity in CsPbBr₃ quantum dots?QDs?with a saturation polarization of 0.25?C/cm².Differential scanning calorimeter?DSC?,X-ray diffraction?XRD?,transmission electronic microscopy?TEM?revealed that the mechanism of ferroelectric-paraelectric switching of CsPbBr₃ QDs can be attributed to the phase transition from cubic phase??to orthorhombic phase?Pna2₁?.In the orthorhombic CsPbBr_3,the distortion of octahedral[PbBr₆]^4-structural units and the off-center Cs⁺generated the slightly separated centres of positive charge and negative charge,resulting in the ferroelectric properties.The variable temperature emission spectrum from 328 K to 78 K exhibits green luminescence and the gradually red shift due to the phase transition.In Chapter three,we prepared a single crystal perovskite CH₃NH₃PbBr₃ with excellent luminescence under a UV excitation.In addition,we proofed that the crystal reversibly undergo a nonpolar-to-polar phase transition at 270K and the space group transforms frominto I4cm,leading to a switchable phase from cubic to tetragonal,and back again.The discovery determined the existence of ferroelectricity in lead halide perovskite MAPbBr₃,which can be generated spontaneous polarization and switched by an electric field.In Chapter four,we dissolve the prepared MAPbBr₃ large crystals,configure them as precursor fluids,spin-coat them on the ITO-coated glass,spray gold on the surface,and explore the ferroelectric properties of MAPbBr₃,so as to truly connect them with solar cell devices.Further,we studied the ferroelectric conversion characteristics of MAPbBr₃ thin films,and prepared ferroelectric solar cells based on inorganic-organic MAPbBr₃ perovskite.The MAPbBr₃ film has a polarized hysteresis loop.The polarization state of ferroelectric methylammonium lead bromide light absorption is closely related to the performance of ferroelectric solar cells.The power conversion efficiency of the ferroelectric solar cell based on the ITO/PTAA/MAPbBr₃/PC₆₁BM/BCP/Ag structure is 8.19%This finding opens up an avenue to explore the ferroelectric-optical properties of inorganolead halide perovskites for high-performance multifunctional materials.