Fabrication And Efficiency Improvement Of White Organic Light-emitting Diodes Based On Solution Processing Electron Transport Layer

White Organic light-emitting diodes?WOLEDs?have attracted much attention and showed great potential in flat panel displays and solid-state lighting due to their simple preparation processes and rich material systems.In general,using the layer-by-layer thermal evaporation,high-performance WOLEDs are easy to be realized.However,some unavoidable disadvantages of this process,such as large equipment investment,material waste,low yield,and difficulty in achieving large area,hinder its further commercialization.Solution processing technology has the advantages of simplicity,low cost and large area preparation,being more suitable for the mass production of WOLEDs.In recent years,nanomaterials have been widely applied in organic light-emitting diodes?OLEDs?,in which the local surface plasmon resonance?LSPR?effect of metal nanoparticles can effectively increase the recombination rate of excitons and improvethe device performance.Therefore,introducing metal nanoparticles in solution-processed OLED devices to improve the device performance is also a very promising research field.This thesis mainly studies the preparation of high-performance WOLEDs based on solution processed electron transport layer?ETL?,and the performance improvement of the WOLEDs by doping silica-coated silver nano-cubes in the electron transport layer.Firstly,we prepared the WOLEDs based on solution processed electron transport layer.The solution deposition of electron transport layers?ETL?may dissolve or mix with the pre-fabricated emission layer?EML?,leading to unfavorable morphologies of interfaces and degradation of device performanceHere,we studied the influence of the host materials of the solution processed EML the solvent,material and preparation process of the solution processed ETL on the device performances.By optimizing the device structure and the preparing process,we greatly improved the performance of the WOLED.Through a large number of experimental studies and comparisons,the optimized device structure is defined as ITO/PEDOT:PSS?45 nm?/PVK:OXD-7:10wt.%FIrpic:0.5wt.%PO-01?50 nm?/TPBi:TmPyPB?7:3??45 nm?/LiF?1 nm?/Al?100 nm?,and the efficiency of the optimized WOELD by all-solution-processing method is 19 cd/AThen,silica coated silver nanocubes?Ag@SiO₂ NCs?were doped in the electron transport layer of the optimized WOLED to improve the device efficiency.The greatly enhanced performance attributes to the strong coupling between the Ag@SiO₂ NCs in electron transport layer and the excitons located near the interface of EML and ETL.Electroluminescence and photoluminescence spectra of the devices declare that the Ag@SiO₂ NCs simultaneously improve the radiation intensities of the blue and the yellow excitons,which enhances the emission intensity of the WOLED,and also helps the WOLED maintain the chromaticity stability.When the concentration of Ag@SiO₂ NCs doped in the electron transport layer is 1.5%,the WOLED achieved a high efficiency of 30 cd/A,being two fold of that of the control device without Ag@SiO₂ NCs incorporated.