Study On Improving The Performance Of Organic Light-emitting Diode Based On Micro-nano Structure

Organic light-emitting diode(OLED)is characterized by light weight,low power consumption,fast response time and flexibility,showing great advantages in flat panel display and solid-state lighting.However,the lower light output coupling efficiency of OLED caused by the light loss mechanisms of substrate mode,waveguide mode and surface plasma modes,which lead to a low external quantum efficiency(EQE).It is an effective method to improve the light output coupling efficiency of OLED by using micro-nano structure.In this thesis,the performance of OLED devices improved by micro-nano structure is systematically studied and analyzed through theory and experiment.The main research contents are as follows:1.Expert OLED simulation software is used to simulate actual OLED devices with different grating structures,and the effects of different micro-nano gratings on the electroluminescence spectrum(EL),luminous Angle and internal electric field intensity distribution of bimetallic electrode OLED devices are analyzed.The micro-nano grating structure is optimized to enhance the luminescence intensity and broaden the luminescence Angle.Under different grating periods,varying the grating height has different effects on the luminescence properties of the devices.By adjusting the molecular dipole orientation in the luminescence layer and optimizing the electric field intensity distribution inside the device,the luminescence performance of the device can be further optimized,thus providing valuable reference for improving the performance of the OLED device by using the periodic micro-nano grating structure in the experiment.2.The quasi-periodic micro-nano structure(PMS)was fabricated by using the phase separation effect of polystyrene(PS)and polymethyl methacrylate(PMMA)blends during the film forming process.The effect of PMS on the photoluminescence of emission layer and electroluminescence properties of OLED were studied.When the PMS was added to the front of the substrate,the photoluminescence spectral intensity of the emission layer increased by 119%,and the EQE of the OLED device increased by42% compared with the control sample.When the PMS was added to the back of the substrate,the photoluminescence spectral intensity of emission layer increased by 59%and the EQE of the OLED device increased by 120% compared to the control sample.The optical simulation of electric field intensity distribution in OLED device is carried out by FDTD simulation.The enhanced performance of OLED devices can be attributed to the reduction of internal surface plasma loss and substrate mode loss by PMS.This work provides a simple and efficient way to reduce the light loss,which will benefit to the low-cost manufacturing process.3.Based on the previous work,the soft nano-imprint method was used to transfer the PMS micro-nano structure to the hole transfer layer of PEDOT: PSS film,and the influence of the PEDOT: PSS film with PMS micro-nano structure on the performance of OLED devices was studied.The surface topography measured by AFM showed that the PMS micro-nano structure were completely copied and transferred to PEDOT: PSS film by PDMS imprint template with unchanged period and size of PMS.Compared with the control device,the maximum brightness,maximum current efficiency,maximum power efficiency and EQE of the OLED device increased by 32%,57%,11% and 51%,respectively.This indicated that the soft nano-imprint method is feasible to transfer the PMS to the hole transport layer of PEDOT: PSS films.The optoelectronic performance of the OLED devices with PMS micro-nano structure was improved by reducing the loss of waveguide mode.