Construction Of Patterned ZnO By Nanoimprint Lithograph To Improve The Light Extraction Efficiency Of The Inverted QLED

Quantum dot light-emitting diode(QLED)has excellent performance such as high brightness,long life,continuous tunable fluorescence spectrum in the visible region compared to Conventional organic light emitting diodes(OLED),widely applied to the field of display and lighting.Although the efficiency,the lifetime,the optimization of driving voltage and brightness of QLED have made great progress in full-color display,there are still some problems such as low device efficiency in the practicable brightness region,high turn-on voltage,non-negligible parasitic electroluminescence(EL)emission toward displays or solid-state lightings.With the increase of the light emitting area,the device must have higher luminous efficiency and instantaneous brightness,but also have good stability under the condition of high brightness.Inverted QLED has the advantages of high efficiency,low turn-on voltage and so on,leading to a potential candidate for future display applications.Due to the internal structure of the QLED device,some of the emitted light is limited by the total reflection,the absorption of the material and the plasmon effect.The most important influence factor is the internal total reflection,which greatly limits its application in the field of commercialization.Many studies have shown that light efficiency of the device has been improved by bringing micro and nano structures such as nano column array,nanorods,grating structure,and microlens structure which can effectively inhibit the total internal reflection.At present,micro-nano structure pattern of technology are the Dip-pen nanolithography,Lithography technology,Nanosphere Lithography and Nanoimprint lithography technology and so on.Compared with the previous techniques,Nanoimprint lithography has the advantages of high resolution,low cost and high yield,and can be used for the preparation of high yield,low cost and large area micro-nano pattern structure,Which providing the choice for higher efficiency in Inverted QLED.As the electron transport layer of the Inverted QLED device,ZnO has the advantages of high transmission rate,strong electron transport ability,good environmental stability and so on.Compared with other layers,it is easier to be patterned.Experiments of concrete work is divided into the following three aspects:1.Preparation and the research of properties of ZnO by atomic layer deposition.By adjusting the temperature and the number of cycles in the experiment,we got the ZnO with film high transmittance(90%)and high electron mobility in 600 cycle,at the temperature of 100 ?.2.Preparation of patterned ZnO thin films.Considering ZnO film itself does not meet the requirements of the traditional Nanoimprint technology,therefore,in this paper,basing on Nanoimprint lithography,we controlled the temperature,pressure and the angle of rotation of the PDMS template in the two impression during the nanoimprint process,the one-dimensional and two-dimensional grating structure could be obtained.And then,we controlled the ICP power sand to obtain a patterned quartz substrate with a period of 750 nm,a line width of 500 nm and a line spacing of 250 nm and a height of 30 nm by inductively coupled plasma etching technology.Then we prepared the patterned ZnO films on the basis of the conditions of previously preparing ZnO thin films by atomic layer deposition.3.Improving the Light extraction efficiency of Inverted QLED by patterned ZnO.The patterned Zn O had a good grating structure and a height of about 30 nm,and we applied the patterned ZnO to the green Inverted QLED.we found that the introduction of the structure eliminates the influence of the waveguide modes between the organic layer and the ITO,and the current efficiency of the Inverted QLED device in patterned ZnO was 2.15 times to the flat film device,while the maximum current efficiency increased from 3.30 cd/A to 7.10 cd/A,increased by 115% compared to the flat film device.