Preparation And Optoelectronic Properties Of Doped Two-dimensional Perovskite (PEA)₂PbI₄ Single Crystal Thin Film

Organic-inorganic hybrid perovskite has become one of the most advanced materials in the field of optoelectronic devices due to its outstanding photoelectric properties,such as high absorption coefficient and long carrier diffusion length.However,there are many defects on the surface and grain boundaries of the perovskite polycrystalline film,which may hinder the final performance of the perovskite device.The two-dimensional perovskite single crystal thin film has no grain boundaries,good material stability and a suitable thickness,making it an ideal research object and is expected to further expand its application range.So far,researchers have applied interface engineering,composition engineering,and device structure design to two-dimensional perovskites to optimize device performance.Among them,the doping system is one of the direct methods to improve the photoelectric performance,but the research on the doping system in the two-dimensional perovskite single crystal thin film is still in the preliminary stage.In this paper,the two-dimensional perovskite(PEA)₂Pb I₄single crystal thin film is ion-doped to improve the photoelectric performance,including adjusting the light absorption range,reducing the density of defect states,introducing new emission characteristics and enhancing material stability.The main contents are as follows:1.The Br-doped(PEA)₂Pb(I_1-xBr_x)₄single crystal thin film was prepared by a space-confined solution temperature-lowering crystallization method.Because the coordination bond strength of(PEA)₂Pb(I_1-xBr_x)₄-solvent determines the solubility of(PEA)₂Pb(I_1-xBr_x)₄,it influences the nucleation rate and crystallization temperature.Therefore,in order to grow high crystalline quality two-dimensional perovskite(PEA)₂Pb(I_1-xBr_x)₄single crystal thin films,we adopted the mixed solvent DMF-GBL to prepare the perovskite precursor solution,and obtained a series of perovskite(PEA)₂Pb(I_1-xBr_x)₄single crystal thin films with accurately adjustable band gaps.The area reached several square millimeters and the thickness ranged from 5 to 8?m.From the SEM morphology characterization,EDS element analysis,XRD structure analysis and optical characteristic analysis,it is proved that the method can control the ratio of bromine and iodine in the single crystal thin film,and realize the accurate adjustment of the band gap.2.The photodetector based on two-dimensional perovskite(PEA)₂Pb(I_1-xBr_x)₄single crystal thin film was designed and prepared.The Au electrode arrays were prepared by using copper mesh instead of the traditional mask,it is possible to prepare nearly a hundred devices on a single crystal thin film at one time,which is expected to realize the application of flexible integrated photodetectors.Because the Br-doped(PEA)₂Pb(I_1-xBr_x)₄single crystal thin film has continuous and adjustable light absorption,the photodetector based on(PEA)₂Pb(I_1-xBr_x)₄single crystal thin film has different photoresponse to light of different wavelengths.These results confirm that both on(PEA)₂Pb(I_0.9Br_0.1)₄and(PEA)₂Pb(I_0.2Br_0.8)₄photodetectors have the superior performance within the corresponding wavelength range,which prove that selective light detection is achieved by Br doping.3.The Er-doped(PEA)₂Pb I₄single crystal thin film was successfully prepared by the space-confined solution temperature-lowering crystallization method,and the effect of metal cation doping on the luminescence performance and luminescence mechanism of perovskite was studied.According to SEM morphology characterization,XRD structure analysis and photoluminescence characteristics analysis,it is proved that Er-doped perovskite(PEA)₂Pb I₄single crystal thin film has a new broad-spectrum emission band at 700 nm.We studied its luminescence mechanism and proved that there is an effective energy transfer process from the host(PEA)₂Pb I₄to the optically active center induced by the Er³⁺to realize the dual spectral emission,which provided some guidance for the research work in this direction.