Applications Of Aluminum Doped Zinc Oxide Transparent Electrode In Quantum Dot Light Emitting Diodes

Quantum dot light emitting diode（QLED）is expected to become the next generation of main lighting display technology,because of its advantages of spectral wider coverage,higher color purity,low energy consumption.These features made it widely applied in mobiles,solid lighting and plate display,especially in the application of light emitting devices of wide gamut.However the research on QLED mostly are still in the experimental stage.In order to realize industrial production,there are many problems to be solved.The main reason for the low efficiency of the device is the imbalance of the carrier injection,which the most common problem is that the hole injection and transmission efficiency is poor.At present,semi-transparent QLED device is the most widely studied,in which tin doped indium oxide（ITO）is used as the most commonly anode materials and the aluminum（Al）or silver（Ag）is used as cathode material.In recent years,the transparent electrode are attracting considerable research attention,such as graphene,aluminum doped zinc oxide（AZO）,fluorine doped SnO₂ and so on.As a transparent electrode,it need to be have high conductivity and high transmittance.Among these transparent conductive film,AZO have attracted considerable attention because of their unique advantages such as abundance of raw material,nontoxicity,high stability in hydrogen plasma,high work function and transmittance.Its conductivity is also comparable with ITO.So,AZO is expected to be used as transparent electrode in the display and light emitting devices.This paper mainly focused on the preparation of AZO thin films by magnetron sputtering,and it was applied to QLED as electrode.At the same time,the green QLED devices were constructed and explore the performance of these QLED devices.The effect of AZO electrodes with different sputtering power on the performance of translucent QLED devices and fully transparent QLED devices were studied.In our work,AZO with higher work function improves the carrier imbalance in the device,effectively promoting recombination of electron and hole,and then improve the efficiency of QLEDs.The detailed work in this thesis can be summarized as follows:（1）Preparation of AZO films with high transmittance and high conductivity by magnetron sputteringThe AZO thin films prepared by different sputtering power showed hexagonal wurtzite structure and preferred growing orientation along（002）.At the same time,the films have high transmittance and high conductivity were prepared.The transmittance of AZO film is between 74.89%and 88.41%at 532 nm;square resistance decreases from 174.70?/□to 2.95?/□with the increasing of sputtering power from 80W to 200 W.Meanwhile,the work function of AZO thin film is close to 5.00 e V.（2）AZO transparent conductive thin films with different sputtering power as anode in QLED devicesAZO transparent conductive films with different sputtering power were used as anode to construct green QLED devices.It is clearly shows that the QLED devices have the best performance when the sputtering power of AZO thin film is 125 W.Under the condition of AZO sputtering power of more than100 W,the hole injection ability is greater than that of the device with ITO as the anode,and the electron-hole injection is more balanced under the condition of AZO power of 125 W and 150 W.The QLED devices were optimized at 125 W sputtering power.The maximum luminance,maximum current efficiency and maximumexternal quantum efficiency(EQE_max)reached 87180 cd/m²,34.90 cd/A and8.71%of optimized devices,respectively.（3）Construction of fully transparent green QLED device with AZO as the cathodeTo construct the fully transparent green QLED device,AZO transparent conductive film was used as the cathode material instead of the opaque electrode（such as aluminum,silver,etc.）.The effect of AZO thin films with different sputtering power was studied on the performance of fully transparent green QLED devices.It is clearly shows that the fully transparent device has the best performance when the sputtering power of AZO film is 100 W and the transmittance of the whole device is 83.83%at 532 nm.The maximum brightness and maximum current efficiency of the top emitting of the transparent device is up to19200 cd/m² and 8.82 cd/A and the maximum luminance and maximum current efficiency at the bottom emitting are 21000 cd/m² and 8.00 cd/A.The brightness and current efficiency of the whole transparent device is up to 40200 cd/m² and 16.82 cd/A.The results show that the thickness of ZnO can effectively improve the magnetron sputtering damage to the device,and when the ZnO is 1500 rpm,the electron-hole injection is more balanced,and the device performance is better.