Application Of High Work Function AZO Transparent Electrode In Quantum Dot Light Emitting Diodes

Quantum dot light emitting diodes?QLED?are expected to become the next generation oflighting display technology,because of its advantages of adjustable emission wavelength in visible range,higher color purity,high brightness and solution-processing.Indium tin oxide?ITO?is used as the most commonly transparent anode materials in conventional QLED device.Concerning the limited abundance of indium,ITO is considered a bottleneck for the possible commercialization of the QLED technology.Therefore,great efforts have been made to develop sustainable alternative transparent electrodes,such as Ag nanowire,graphene,carbon nanotubes and transparent conductive oxide?TCO?films.Among them,aluminium-doped zinc oxide?AZO?has attracted considerable attention because of their unique advantages such as abundance of raw material,nontoxic and transmittance,which is the most competitive alternative for the next generation of transparent electrodes.However,when the AZO conductive films with high work function is used as the electrode to construct QLED device,its large surface roughness will lead to larger leakage current,which further affects the performance of the device.This dissertation mainly discusses the application of AZO by magnetron sputtering as anode tofabricate QLED device.The flatness of AZO film is improved by controlling sputtering pressure,and the leakage current of the device is reduced.In addition,the AZO anode with high work function can improve the injection efficiency of holes and make the carrier injection more balanced.Detailed research work can be divided into the following three aspects:?1?Preparation of aluminum-doped zinc oxide transparent conductive film by magnetronsputteringFirstly,the effects of different sputtering power on the crystallinity,morphology and photoelectricproperties of AZO thin films were studied.The results show that AZO thin films could meet the requirements of high transmission and high conductivity as transparent electrodes when the sputtering power is 125 W.At this power,the effect of sputtering pressure on the surface morphology and photoelectric properties of AZO films was investigated.The results show that the crystallinity and photoelectric propertie of the films do not change significantly with the decrease of sputtering pressure?from 2.5 mTorr to 0.5 mTorr?:the square resistance of the films is below of 20?/?,and the grains grow preferentially along the direction of?002?.At the same time,the surface roughness of AZO films decreases from 5.25 nm to 2.32 nm,and the work function of AZO films is about 5.03 eV.?2?Application of AZO transparent conductive film as anode in green QLED deviceQLED devices were firstly fabricated with AZO thin films prepared by different sputtering poweras anodes.The results show that the device performance is the optimal when the sputtering power of AZO thin films is 125 W.The AZO thin films fabricated by higher sputtering power will cause larger leakage current,which will lead to a decrease in device efficiency.The performance of QLED devices constructed by AZO thin films with different sputtering pressures show that the device has the best performance when the sputtering pressure of AZO thin films is 1.0 mTorr.The maximum brightness,current efficiency and maximum external quantum efficiency(EQE_max)of the optimized device are 102500 cd/m²,51.75 cd/A and12.94%,respectively.And high reproducibility of the QLED devices based-AZO could be obtained.Combining the film-forming properties of AZO/PEDOT:PSS,AZO/PEDOT:PSS/TFB films and the performance of single carrier devices at different sputtering pressures,it is found that when the sputtering pressure of AZO films is 1.0 mTorr,the electron-hole injection is more balanced.?3?Introducing inorganic metal oxide V₂O₅ to improve the stability of QLED devicesInorganic metal oxide of V₂O₅ is introduced into AZO-based QLED devices.Three kinds of holeinjection layer devices are designed:V₂O₅,V₂O₅/PEDOT:PSS and V₂O₅-PEDOT:PSS.Combined with the energy level of V₂O₅ and PEDOT:PSS,the device with V₂O₅-PEDOT:PSS mixed hole injection layer has the lowest hole injection barrier and the best device performance.Based on this,after optimizing the ratio of V₂O₅-PEDOT:PSS,ultraviolet ozone time,thickness and the thickness of other functional layers,the maximum brightness,current efficiency and EQE_max of the device reach 98300 cd/m²,55.53 cd/A and13.85%,respectively.Compared to control device,the operation lifetime increased about three times after introducing of V₂O₅,reaching 9051 hours.High reproducibility of the QLED devices based-V₂O₅-PEDOT:PSS HIL could be obtained.At the same time,the introduction of V₂O₅ also solves the problem of carrier imbalance caused by excessive hole injection efficiency in AZO electrode QLED devices.