Investigation Of Magneto-Optical Effect For Chiral And Achiral Perovskites

Chiral perovskite is one of the novel semiconductor materials at this stage,which can be mainly used in the fields of circularly polarized light emission and detection.The combinations of natural optical activity and spintronic properties for chiral perovskites are expected to broaden the scope of chiroptical spintronic research.Chirality-induced spin-orbit coupling of chiral perovskites is a kind of unique physical property in chiroptical spintronic,which provides a theoretical basis for realizing the magneto-optical-electric effect of chiral perovskites.However,the spin-related magneto-optical effect research based on chiral perovskites is developing nowadays.Thus,this paper focuses on the magneto-optical effect of chiral perovskite,as well as analyzes the influence of factors such as circularly polarized light,magnetic field,temperature,and precursor solution concentration on the magneto-optical effect of chiral perovskite single crystal and polycrystalline thin films.The spin-dependent photophysical processes of chiral perovskites are demonstrated in detail through the combination of experiment and theory.The specific research contents are as follows:（1）Chiral perovskite single crystals（R-MBA）₂Pb I₄ and（S-MBA）₂Pb I₄ with high crystal orientation were synthesized by a low-temperature solution method,and their magneto-photoluminescence（Magneto-PL）effects were studied.We found that Magneto-PL exhibited a negative signal and was positively correlated with temperature.As well as circularly polarized light can control the Magneto-PL effect.Theoretical analysis shows that the Magneto-PL effect of chiral perovskite single crystals is caused by the difference in the number of photoinduced exciton states.In addition,their electron paramagnetic resonance and time-resolved photoluminescence spectra confirmed that chirality can be transferred to exciton states,photogenerated paramagnetic species,and electron-hole pairs,resulting in the spin-related g-factor and electron-hole lifetime that follow the circular dichroism.This work provides an idea for magnetic field regulation of chiral perovskite single crystal luminescence.（2）Based on advantage of the solution processability of chiral perovskite single crystals,the（R-MBA）₂Pb I₄ and（S-MBA）₂Pb I₄ polycrystalline films were prepared,respectively.At room temperature we observed that（R-MBA）₂Pb I₄ and（S-MBA）₂Pb I₄films not only possess circular polarization,but also generate an obvious negative Magneto-PL effect.In addition,the experiment results demonstrated that both the circular polarization and Magneto-PL effect of（R-MBA）₂Pb I₄ and（S-MBA）₂Pb I₄ films increase with decreasing temperature.It notes that the constant magnetic field does not change the dependence between temperature and circular polarization,but can change circular polarization strength.Through the combination of experiment and theory,we established the effective mass model of the exciton state,and systematically revealed the spin-photophysical process inside the chiral perovskite polycrystalline thin film.This work provides an effective way to manipulate the circular polarization and luminescence of chiral perovskite polycrystalline thin films.（3）We prepared chiral perovskite polycrystalline films with different concentrations and measured their magneto-optical effects.It is found that the magneto-optical effect can be controlled by solution concentration.Based on the characterization of chiral perovskite polycrystalline films with different concentrations by scanning electron microscopy,X-ray diffraction patterns,and grazing incidence wide-angle X-ray scattering patterns,we demonstrated that the solution concentration are closely related to the surface morphology,crystalline orientation and strain.The concentration-dependent long-range and short-range crystalline chiral perovskites can be generated to manipulate their natural optical activity,resulting in the concentration-dependent magneto-optical effect.This work provides experimental and theoretical guidance for tunable and large magneto-optical effects of chiral perovskites.（4）We fabricated the chiral perovskite-based optoelectronic device,and found that the photocurrent of the device strongly depends on the polarization of the incident light,resulting in an obvious circular photogalvanic effect（CPGE）.As well as the CPGE is dependent on the helicity of the material.We proposed that CPGE is caused by Rashba band splitting of chiral perovskites.Due to the presence of chirality-induced spin selectivity,the in-plane spin-polarized photogenerated carrier and exciton transport processes are related to the helicity of the material.In addition,these experimental results are also verified by the incident polarization light-dependent PL intensity variation.This work provides a theoretical basis for spin transport of chiral perovskite spintronic devices.（5）We prepared traditional achiral three-dimensional(MAPb I_3-xCl_x)and quasi-two-dimensional(（PEA）₂（MA）₃Pb₄I₁₃)perovskite-based spin valve devices.Achiral perovskite devices exhibit the obvious magnetoresistance effect（MR）at room temperature,and the ferromagnetic/perovskite interface can enhance the magneto-photocurrent（MPC）effect of 3D and quasi-2D perovskite devices.We infer that orbital hybridization occurs between the ferromagnetic and nonmagnetic perovskite interfaces,forming the spinterface and the spin-dependent interface density of states.The ferromagnetic/perovskite spinterface and perovskite contribute to the MR and MPC of the spintronic device.This work provides theoretical guidance for manipulating spin-polarized electron transport at the ferromagnetic/perovskite spinterface and realizing the strong magneto-optical effect.