Research On The Preparation And The Properties Of Organic-Inorganic Hybrid Perovskite Thin Films

As a candidate material for the next generation of semiconductor light-emitting and photovoltaic devices,organic-inorganic hybrid perovskite materials have attracted wide attention due to their excellent photoelectric properties.It has high absorption coefficient,long electron-hole diffusion length,low deep-level defect state density,adjustable optical band gap and simple preparation process.Compared with all inorganic lead halide perovskite materials,organic-inorganic hybrid perovskite has broken through the instability caused by moisture and photothermal to a certain extent,and has more stable crystal structure and performance.In recent years,among organic-inorganic hybrid perovskite materials,perovskite materials with quasi two-dimensional structures have attracted widespread attention due to their combination of the environmental stability of two-dimensional(2D)perovskite and the outstanding photoelectric properties of three-dimensional(3D)perovskite.However,their formation mechanism and performance control are still hot issues in this field,requiring systematic and in-depth research.In this paper,two schemes,namely,tuning(PEA)2PbI4 perovskite by Cs+ions and mixing homologous organic short chain MA+/FA+with(PEA)2PbI4,were used to prepare quasi-two-dimensional(quasi-2D)perovskite thin films with high photoelectric performance and stability at room temperature using a one-step spin-coating method.The structure and properties of the quasi two-dimensional perovskite material were systematically studied.The main research contents are as follows:(1)In this paper,2D(PEA)2PbI4 hybrid perovskite films were prepared by one-step spin-coating method at room temperature.Based on the synthesis of(PEA)2PbI4,inorganic Cs+ions were doped in the film to investigate the influence of Cs+doping on the structure and properties of(PEA)2PbI4 perovskite films.The results show that both as-grown(PEA)2PbI4 film and Cs+-doped(PEA)2’bI4 films exhibit the instinct of the layered structure,though Cs+ions doping would make the 2D structure weakened.Through analyzing the optical properties,it is found that,besides the 2D(PEA)2bI4 phase,a quasi-2D structure with two layers of[PbI6]4--octahedron forms in Cs+-doped(PEA)2PbI4 perovskite films,which is ascribed to the phase rearrangement of the(PEA)2PbI4 crystal structure under the induction of Cs+ions.(2)In addition,quasi-2D(PEA)2(MA/FA)n-1PbnI3n+1(n=1,2,3 and 4)perovskite thin films were also prepared using a one-step spin-coating method,and the crystal structure and optical properties of the material were studied.The results show that the introduction of short-chain organic cations makes the crystal structure of perovskite expand from pure 2D to quasi-2D layered structure which tends to 3D.Although the appearance of quasi-2D phase makes the film morphology rough,the long-chain organic PEA+ cations with hydrophobicity encapsulates MA+ and FA+ which are easily affected by the environment in the layered structure of perovskite,which ensures the stability of as-prepared perovskite films.With the introduction of MA+/FA+,the[PbI6]4--octahedron layer in the inorganic layer gradually increases from 1 to 4,and the film shows a tuned direct band gap.In addition,the quasi-2D perovskite thin film material also has excellent light absorption characteristics and environmental stability.In this thesis,the research on the preparation methods and formation mechanisms of quasi-2D organic-inorganic hybrid perovskite materials provides basic data for the structure and performance regulation of organic-inorganic hybrid perovskite materials,and has positive significance for promoting the application of organic-inorganic hybrid perovskite materials in multiple fields.