Study On Properties And Electric Field Control Of Quasi Two-dimensional Perovskite Optoelectronic Devices

Quasi two-dimensional metal halide perovskite has good photoelectric properties and environmental stability.It is one of the most promising materials for the preparation of long-term stable and high-performance perovskite devices.It has attracted extensive research interest in recent years.This paper focuses on the features of optical properties,film morphology,crystal structure,phase distribution and orientation between RP type and DJ type quasi two-dimensional perovskites,as well as the influence of polarization on the performance and working state of photovoltaic and LED devices.The main research contents of this paper can be divided into the following three aspects:（1）A high-performance planar quasi-2D OIHP solar cell comprising（PEA）₂（MA）₃Pb₄I₁₃（n=4）is designed.It displays a large area coverage and an interconnected nanorod network,which contributes to efficient light absorption and charge carrier transport.The surface and dipolar polarizations exhibit the remarkable light intensity and electric field–dependent characteristics at shortcircuit-current(J_sc)and steady-state(i.e.,V_oc)conditions.More importantly,V_oc exhibits a nonlinear behavior at steady states.Such a unique feature is accordance with the dipolar polarization measured at the same condition.The phenomenon can be explained by the significant dipole–dipole interaction at lower electric field strengths.At higher field strengths,the screen of the dipoles due to charge accumulation at the surface of the organic cation spacer leads to slower increment of V_oc.Thus,carefully designing the quasi-2D perovskite nanostructure,together with the dielectric property of the organic cation spacer,may play an exceptionally important role for future high-performance quasi-2D perovskite solar cells.（2）we examine the excessive-salt-assist（ESA）process cooperating with the antisolvent treatment method in Dion-Jacobson type Perovskite LEDs.The ESA process combined with anti-solvent treatment can fill the vacancies in（PDMA）（FA）₂Pb₃X₁₀perovskite,modify the surface defects of the film,and reduce the hole injection barrier,so as to enhance the radiation recombination,reduce the trap density of states,and improve the hole transport and injection.By investigating the electric-field driven polarization process,we reveal that the more important to improve the device performance is to construct an efficient interface with minority carrier transport layer for surface polarization that could promote the charge carrier injection and recombination for high-performance LED devices.Accordingly,the DJ type quasi 2D perovskite LED based on PDMA group has a high external quantum efficiency（EQE）of 7.1%and enhanced stability.（3）In DJ perovskite,the bimodal amino BDA without benzene ring is introduced as the spacer cation,which reduces the space resistance and the possibility of the distortion of the perovskite layer.The synergistic effect of ESA and anti-solvent treatment was applied to the fabrication of perovskite.The LED device has obtained 7.0%of the external quantum efficiency and the radiation intensity comparable to the three-dimensional perovskite led.The improvement of device performance and brightness can be attributed to the increasing transmission performance and the decreasing trap state of density caused by small interval cations,which are due to the crystalline enhancement,orientation change and defect filling of perovskite.The DJ perovskite of BDA group also shows the insensitivity to the substrate selection,which has certain advantages for the process control in large area and flexible preparation.BDA based perovskite LED also improved the potential barrier and stability of cavity injection,which indicates that the treatment of synergistic effect has a universal regulatory effect on DJ type perovskite LED.Finally,the polarization characteristics of the devices in the working state are studied by the same method.The surface polarization bulk junction formed by perovskite and hole injection layer TFB plays an important role in improving the injection and recombination of the minority carriers.