Research On Transparent Electrode With Dielectric/Metal/Dielectric Structure In OLED

Transparent conducting electrode is a major factor on influencing the optical properties of Organic Light Emitting Diode(OLED)including the luminance and spectral distribution,which will affect the external quantum efficiency of device.Designing and preparing transparent electrode with high conductivity and transmittance is one of the important ways to improve the performance of OLED device.In recent years,Dielectric/Metal/Dielectric(DMD)transparent conducting film with stacked structure has been favored by researchers because of its good conductivity and transmittance.In this paper,different combinations of dielectrics and metals are used to carry out the research on transparent conducting electrode of stacked structure DMD in OLED.The research work in this thesis is mainly divided into three parts: optical simulation of stacked transparent electrode,optimization of electrode structure parameters,and optimization of OLED performance.(1)Optical simulation of transparent electrode with stacked structure and calculation of electrode transmittance.The theoretical methods of electrode optical simulation and transmittance calculation in the thesis are multi-beam interference method and transmission matrix method.According to the above two theories,Matlab is used for programming.The optical constants of materials used in the theoretical calculation are all measured by ellipsometry.The theoretical simulation results are basically consistent with the experimental measurement results,indicating that optical simulation calculation has a guiding role in the design of electrode structure parameters.(2)Optimization of transparent electrode structure parameters.The electrodes are prepared by vacuum thermal evaporation.The electrode structures are: MoO3/Ag/MoO3?MoO3/Cu/MoO3?MoO3/Al/MoO3.Based on the optical and electrical characteristics of electrode,the thicknesses of light outcoupling layer MoO3,intermediate metal layer and hole injection layer MoO3 are optimized respectively.The results of electrode parameter optimization show that the transparent electrode with metal Ag as the intermediate metal layer has the optimal photoelectric performance.(3)Using transparent electrode with DMD structure in OLED devices and optimizing device performance.OLED devices are prepared by vacuum thermal evaporation,and the device structure is Quartz glass/MoO3/metal/MoO3/NPB /Alq3/Liq /Al.Through the test and analysis of photoelectric performance of device,it is found that the device efficiency using DMD electrode with optimal structure parameter is unsatisfactory.According to the island-like growth characteristics of metal film,a metal layer can be evaporated under the metal layer to increase the wettability and reduce the metal surface roughness.Therefore,a double interlayer(D/M1/M2/D)electrode structure is proposed.When the fabricated device structure is Quartz glass/MoO3(20 nm)/Cu(3 nm)/Al(12 nm)/MoO3(20 nm)/NPB(45 nm)/Alq3(60 nm)/Liq(1 nm)/Al(100 nm),the device is the brightest.Comparing with the structure of Quartz glass/MoO3(20 nm)/Al(15 nm)/MoO3(20 nm)/NPB(45 nm)/Alq3(60 nm)/Liq(1 nm)/Al(100 nm),the turn-on voltage of device is also reduced by 0.2 V,and the current efficiency is increased by nearly 10 times.This result shows that the structure of double layered metal can provide new ideas for the subsequent design of stacked electrode structure.