Application Of Silver Nanowires/aluminum Doped Zinc Oxide Composite Electrode In Fully Transparent Quantum Dot Light Emitting Diodes

Due to the narrow spectral emission bandwidth,high brightness,solution process and tunable emission wavelength over the entire visible region,quantum dot light-emitting diodes(QLED)have great potential application in flat panel displays and solid state lighting.Display panel based on QLED have excellent color gamut,low energy consumption and high color purity.With the advancement of technology,it is no longer limited to semi-transparent devices.The research on the construction of fully transparent QLED devices have been deepening.The fully transparent devices have great application in the future display field,such as high definition displays,shop windows,information bulletin boards,sightseeing elevators,and vehicle glass.For fabricating a fully transparent QLED,the electrode material require high conductivity and transmittance.The most common transparent conductive electrodes are graphene,Ag nanowires(AgNWs),aluminum doped zinc oxide(AZO),fluorine-doped tin oxide(FTO)and so on.The AgNWs prepared by solution method has the advantages of low cost and easy processing.However,there are some defects such as poor adhesion on the substrate,large resistance between the wire and the wire.Combining the excellent conductivity of Ag nanowires and the uniform and dense of AZO thin films,AZO thin films are deposited on AgNWs films.This composite electrode can reduce the contact resistance and increase the adhesion of Ag nanowires to the substrate.In this dissertation,the transparent conventional and inverted QLED devices were constructed by AgNWs/AZO composite electrodes as electrode and ZnCdSeS/ZnS quantum dots as the emitting layer.On this basis,adjust the thickness of AZO and improve the performance of the device.(1)Preparation of AgNWs/AZO composite electrodeIn order to prepare AgNWs/AZO composite electrode with high conductivity and high transmittance,AZO films with different Al doping concentrations were prepared by atomic layer deposition.The structure,transmittance and conductivity of AZO films were investigated by changing Al doping concentration.When the Al/Zn cycle ratio is 1/17,that is,the doping concentration of Al is 5.26%,the transmittance of AZO film is the highest and the resistivity is the lowest.The AgNWs films with different Ag concentration were prepared by spraying method.The results show that the square resistance and transmittance of the AgNWs solution are consistent with the requirements of transparent electrodes when the concentration of AgNWs solution is 8 mg/mL.Therefore,combining the optimal cycle of Al/Zn with 1/17,AZO films deposited on AgNWs film(AgNWs/AZO)or below(AZO/AgNWs),two different composite electrodes were constructed,respectively.By comparing the square resistance of three electrodes of AgNWs,AgNWs/AZO and AZO/AgNWs after adhesive tape adhering,it is found that it can not only reduce the contact resistance between the AgNWs lines for improving the conductivity of the electrode,but also enhance the attachment of the AgNWs to the substrate only when the AZO is deposited on the AgNWs films.(2)AgNWs/AZO composite electrode as cathode in transparent conventional QLED devicesTo further prove that the composite electrode with AgNWs/AZO structure having better performance than the other two electrodes,three conventional transparent QLED devices with different cathode structures of AgNWs,AgNWs/AZO and AZO/AgNWs were constructed.By comparison,the QLED devices with AgNWs/AZO composite electrodes exhibit the best performance.The maximum current efficiency of the device reach 11.55 cd/A,which is doubled compared to device with pure AgNWs electrode.With the increase of AZO thickness,the current efficiency increases firstly and then decreases of the fully transparent conventional QLED devices.When the AZO is 35 nm,the resistance of the AgNWs/AZO composite electrode is smaller,the contact with the electron transport layer is better and the performance of device iis the best.After optimization,the maximum brightness and current efficiency are 15927 cd/m~2 and 14.00 cd/A,respectively.At 5 V voltage,the bottom(ITO)and the top(AZO)emit green light at the same wavelength(530 nm).The overall transmittance of fully transparent conventional devices are above 60.00%at the wavelength of 530 nm.(3)AgNWs/AZO composite electrode as anode in transparent inverted QLED devicesThree kinds of transparent inverted QLED devices were constructed by taking AgNWs,AgNWs/AZO,and AZO/AgNWs electrodes as anodes,ZnCdSeS/ZnS quantum dots as luminescent layers.Similar to those of conventional QLED devices,the performance of transparent inverted QLED device can also be improved when AZO was deposited on AgNWs films.When the thickness of AZO is 20 nm,the device performance was the best and the transmittance of the AgNWs/AZO composite electrode is 78.91%at 530 nm.The maximum brightness and current efficiency of the device are 18407 cd/m~2 and 15.33 cd/A,respectively.And the overall transmittance of the fully inverted device was 75.60%at 530 nm.At 8 V voltage,the device emit green light of the same wavelength(530 nm)at the bottom(ITO)and top(AZO).