Study On Photoelectric Properties And Devices Of Quasi-two-dimensional Perovskites

The organic/inorganic hybrid layered quasi-two-dimensional perovskites are formed by an ordered self-assembly method of organic molecules and inorganic molecules.In the framework of these perovskites,the inorganic component forms an extended skeleton through a strong covalent bond or an ionic bond,and then the organic component is filled into the frame to present an alternating structure with the inorganic layer.The alternately stacked organic/inorganic layers would result in a similar multiple quantum well structure in the quasi-two-dimensional perovskites,which exhibits larger exciton binding energy and more prominent light,electrical,magnetic properties compared to those of the three-dimensional perovskites.In addition,a significant advantage of this type of material is the flexible to regulate the material structure to achieve the desired results according to the performance requirements of the device.Therefore,such quasi-two-dimensional perovskites show an outstanding value in photoelectric applications.In this paper,lead iodide?PbI₂?was selected as the inorganic component.The basic structure and photophysical properties of such quasi-two-dimensional hybrid perovskite materials were studied by changing the number of inorganic layers between organic layers and organic cations,and corresponding photoelectronic devices were prepared to study the effect of structural changes in the material on device performance.The main research contents of this work are listed as follows:1.Three kinds of quasi-two-dimensional hybrid perovskite materials with different inorganic layer numbers were synthesized by solution cooling method:?PEA?₂?MA?_n-1Pb_n I_3n+1?n=1,2,3?.The chemical composition of the product is analyzed by elemental analysis?EA?,and the microscopic structure and surface morphology of the product were characterized by X-ray diffraction?XRD?,Fourier IR?FTIR?and Scanning electron microscopy?SEM?.2.The two-dimensional hybrid perovskite materials synthesized from three different inorganic layer numbers were dissolved in DMF and the thin films were prepared by rotation coating.It was characterized and tested by XRD,Ultraviolet visible absorption spectrum?UV-Vis?and Surface photovoltage spectrum?SPS?.Through analysis,it is found that the crystallinity of the film is stronger than that of the solid powder material,and as the number of inorganic layers increases,the absorption peak gradually red-shifts,and the band gap decreases accordingly,but the photoconductivity of the film is gradually enhanced.We have fabricated the corresponding photodetectors using these three materials,and its structure is:ITO/PEDOT:PSS/Perovskite/PCBM/LiF/Al.The device was tested for performance based on UV-Vis selected excitation light at a specific wavelength.Among them,the performance of the photodetector based on?PEA?₂?MA?₂Pb₃I₁₀ is better:the light response rate is 1975.0mA/W,the light detection rate is 3.11×10¹55 cm·Hz^1/2/W,the light-on ratio is 3.1×10⁵,and the rise and fall times of the optical response respective are 5 ms/4 ms under the bias of 0 V and607 nm?0.2 mW/cm²?illumination.3.The organic cation was replaced with FA⁺,and the quasi-two-dimensional hybrid perovskite?PEA?₂?FA?_n-1Pb_nI_3n+1?n=2,3,5?film with different inorganic layer numbers was prepared by one-step spin-coating method.XRD,SEM,atomic force microscopy?AFM?,UV-Vis,photoluminescence spectroscopy?PL?and ultraviolet photoelectron spectroscopy?UPS?were used to analyze the structure,film morphology and photophysical properties,and we found that as the number of inorganic layer increases,the photoluminescence peak of the perovskite film gradually red-shifts,and the band gap decreases accordingly.Based on these three kinds of thin film materials,we have fabricated a deep-red electroluminescence device whose structure is:ITO/PEDOT:PSS/Perovskite/Bphen/LiF/Al.The LEDs exhibit the deep-red electroluminescence?EL?peaks of 720 nm?n=2?,745 nm?n=3?and 764 nm?n=5?,respectively.The optimized device?n=2?exhibits a turn-on voltage of 4.2 V,a maximum luminance of 230 cd/m²,and a maximum current efficiency of 0.44 cd/A with the CIE coordinate of?0.691,0.291?.In addition,we have also successfully fabricated light-emitting devices on flexible substrate based on the optimized device structure and analyzed its light-emitting mechanism.