Investigation Of The Growth And Photoelectric Properties Of Two-Dimensional Lead Iodine Compound Highly Preferred Oriented Films And Three-Dimensional Perovskite Single Crystals

Hybrid organic-inorganic lead halide perovskites have been intensively investigated due to their extraordinary optoelectronic properties such as long electron-hole diffusion length,high carrier mobility,low manufacturing cost,and superior quality in high absorption coefficient.However,the poor chemical stability is a severe problem to prevent the application of perovskite optoelectronic devices.Compared with polycrystalline perovskite film,single crystal perovskites show higher stability toward ambient erosion,moisture,and high temperature.Otherwise,single crystal perovskites show longer carrier lifetime and lower trap-state-density,which makes up for the shortcomings of perovskite thin films.In this paper,the growth process and photoelectric properties of 2D lead iodine compound highly oriented films and 3D single crystal perovskite are studied:1?Highly oriented lead iodide(Pb I₂)film was spin coated on gallium nitride(Ga N)single crystal substrate,and highly oriented CsPbBrI₂inorganic perovskite film was grown on single crystal silicon substrate.X-ray diffraction(XRD)and Raman spectroscopy were used to analyze the compressive stress of lead iodide film on Ga N substrate.Photoluminescence spectrum and Raman spectrum were used to analyze the compressive stress of CsPbBrI₂ film on Si substrate.The lattice structure of CsPbBrI₂ inorganic perovskite was confirmed to be tetragonal by density functional theory calculation.2?A series of perovskite(Cs_xMA_1-xPbBr₃)single crystals were grown by adjusting the concentration of Cs⁺ranging from 0%to 4%in the saturated solution.The properties of different single crystals were analyzed by X-ray diffraction,photoluminescence spectrum,time-resolved photoluminescence spectrum and X-ray photoelectron spectroscopy.Cs_0.02MA_0.98PbBr₃ shows the best optical properties of the smallest defect density and the longest carrier lifetime.Photodetectors were fabricated by depositing 100 nm thick Cu interdigital electrodes via vacuum evaporation on single crystals.The responsivity,detectivity,and response speed were measured,and the results show that Cs-doping can effectively improve the electrical performance.The Cs_0.02MA_0.98PbBr₃single crystal photodetector shows the highest responsivity and detectivity,reaching 1.09 A/W and 3.17×10¹¹ Jones at 5 V bias voltage,respectively.The effects of Cs-doping on the lattice structure of MAPbBr₃ were calculated by density functional theory.The results show that Cs-doping can lead to lattice relaxation of MAPbBr₃ and decrease of the defect density.Cs-doping cause the movement of Pb-6p orbital energy level towards lower energy region and the decrease of the band gap of MAPbBr₃.