Resonance Enhanced Metasurface In Lead Halide Perovskite Films

Contributing to the rapid development of micro-nano fabrication,the metasurface made plentiful breakthroughs in the field of high-performance miniature photoelectric device in recent years.The metasurface has an important value in the field of nonlinear optics,which can control beam polarization direction,amplitude and phase through regulating the material composition,size,shape and configuration.The development of optics is inseparable from materials.Organic and inorganic lead halide perovskite?CH₃NH₃PbX₃,X=Cl,Br,I?is regarded as a promising photoelectric material due to its excellent properties such as fast carrier migration,long exciton diffusion length,tunable band gap,high efficiency photoluminescence and low cost.At present,a series of perovskite-based photonic devices have been successfully prepared,such as perovskite-based solar cells,photodetectors,light-emitting diodes,micro-nano lasers,and have extended their practical applications to display,imaging and sensor fields.In addition,the organic and inorganic lead halide is an excellent nonlinear optical material with high refractive index and high nonlinear coefficient.However,until now,the experiment of combining the nonlinear optical properties of perovskite with the metasurface is still insufficient,and relevant devices have not been developed.In view of above situation,this paper proposes a resonance-enhanced metasurface based on perovskite thin film,which can realize high-density encryption and reading of specific information through a layer of thin film structure.It is of great value for anti-counterfeiting,information encryption,information processing and optical storage.In order to meet the preparation requirements of the metasurface,a rapid and low-cost reverse solvent spin-coating method with both film quality and precursors was used to prepare the perovskite film.The film thickness and surface roughness can be precisely controlled by adjusting the concentration of the perovskite precursor,spin coating speed and the addition time of chlorobenzene.At the same time,a kind of grating resonance-enhanced metasurface is designed by the electromagnetism module of COMSOL Multiphysics software,and its structural parameters such as period,spacing and thickness are optimized to achieve the effect of enhance the electromagnetic field.Then,the experimental sample of design parameters was prepared by electron beam exposure and dry etching technology.As a result of the enhancement of local electromagnetic field,nonlinear processes in perovskite films have been enhanced,mainly including the Third Harmonic Generation?THG?and three-photon Absorption?TPA?processes.Thus,the metasurface of perovskite grating can only be observed with strong green three-photon up-conversion fluorescence under the excitation of pump light at the designed wavelength.This particular advantage has a wide range of applications,such as optical printing display and optical encryption coding field.Only when the wavelength of incident pump light is the designed resonance wavelength,the coded information can be seen.Pumping light of non-design wavelength or single photon excitation can only see the uniform dark or green fluorescence background that cannot show the hidden coding information.