The Effects Of WO_x,ZnO And Their Doping As Interfacial Materials On Photoelectric Properties Of Ultraviolet OLEDs

Organic electroluminescent devices（OLED）have high application value in the field of full-color display lighting because of their bending and folding,wide color rendering range,energy saving and environmental protection,low power consumption,low voltage drive,autonomous luminescence and other advantages,and are considered as the"display star"in the 21st century.Ultraviolet（UV）OLED with short-wave emission is widely used in excitation light source,high-density information storage,biochemical sensing and other fields,and has greatly expanded the application range of optoelectronic devices.However,there are still many problems to be solved.For example,indium tin oxide（ITO,whose surface work function is 4.7 e V）transparent electrode,as a commonly used OLED electrode material,does not match the energy level of ultraviolet luminescence material seriously,resulting in unbalanced carrier transmission and low device efficiency.In order to solve the above problems,WO_x,ZnO and their doped materials synthesized by sol-gel method were used to modify the interface of ITO electrode,improve the surface morphology of ITO and reduce the carrier injection barrier,so as to prepare high performance UV OLED.Specific research contents are as follows:1)WO_xalcohol solution was synthesized by sol-gel method and doped with PEDOT:PSS as a composite hole injection layer（PEDOT:PSS+WO_x）,which effectively modified the ITO anode to prepare UV OLED with PBD as the luminous layer.Using X-ray diffraction（XRD）,atomic force microscopy（AFM）,scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）and other characterization tests,it is proved that PEDOT:PSS+WO_xcomposite layer films have excellent surface morphology and photoelectric properties.Compared with other reference devices,the UV OLED prepared based on PEDOT:PSS+WO_xcomposite hole injection layer has better photoelectric performance.The optimal emission peak of the device is located at 400 nm,and the half-peak width is 47 nm.The maximum irradiance is 3.98 m W/cm²and the maximum external quantum is 2.3%.In addition,the process of charge transfer from PEDOT to WO_xwas further illustrated by ultraviolet photoelectron spectroscopy（UPS）and impedance spectroscopy,which proved that the hole injection/extraction ability of PEDOT:PSS+WO_xcomposite hole injection layer was improved,which helps to regulate the carrier balance in the luminous layer,thus improving the photoelectric performance of UV OLED.2)Polyethylene glycol（PEG）was used to modify ZnO solution（ZnO+PEG）,and ZnO+PEG mixed solution was used to modify the surface of ITO,which could effectively isolate the influence of water and oxygen in the air on Cs₂CO₃.In this study,an inverted NUV OLED was prepared by using（ZnO+PEG）/Cs₂CO₃composite electron injection layer and PCZTZ luminescence layer.The maximum irradiance（10.6 m W/cm²）and the maximum EQE（1.9%）of the device are obtained.The emission peak is located at 409 nm and the half peak width is 52 nm.It is proved that the photoelectric performance of the device based on（ZnO+PEG）/Cs₂CO₃composite electron injection layer is significantly better than that of the reference device using other electron injection layer.It is proved that（ZnO+PEG）/Cs₂CO₃has excellent morphology and electronic properties by XRD,SEM,AFM and XPS.Formore,the high electron injection capability of（ZnO+PEG）/Cs₂CO₃was further demonstrated by the voltammetry characteristics and impedance spectra.Therefore,the use of（ZnO+PEG）/Cs₂CO₃composite electron injection material provides an effective method for the preparation of high efficiency inverted NUV OLED.