Preparation Of Patterned PEDOT:PSS And Its Application In Quantum Dot Light-Emitting Diodes

Compared to organic light emitting devices, quantum dot light emitting diode(QLED) has excellent performance such as high brightness, pure color, long life in the field of color display, and simple process, low cost and good operation stability in the preparation process. After the CRT TVs are replaced by the LCD TVs, QLED is one of the most promising high-tech products to replace LCD to open the industrial revolution in the field of display. However, the external quantum efficiency is exactly low due to the serious internal total reflection, which is a major factor limiting the commercialization of QLED. Numerous studies have shown that the light extraction efficiency has been enhanced, when the proper period of micro-nano structure arrays were insert the optoelectronic device with "sandwich" structure, such as moth eye structures, photonic crystals, micro lens and a variety of one-dimensional and two-dimensional micro-nanostructures. Nowadays, the mainstream of micro-nano structure processing tools are traditional lithography, electron beam lithography, focused ion beam lithography and nanoimprint lithography, etc. However, there is a limit resolution in lithography technology, direct writing technology has low capacit of products, and nanoimprint can achieve a large area, the preparation of micro- and nanostructures low cost and high yield which is an appropriate choice for QLED performance improvement. The spin-coated PEDOT: PSS film with high conductivity, high transmittance is commonly used as QLED hole transport layer material, which is stable in the atmosphere compared to other layers in terms of micro-nano fabrication. However, the characteristics of PEDOT:PSS itself does not meet the requirements of traditional nanoimprint technology. Here, combining with reactive ion beam etching and glycerol modifications, we come up wih two advanced PEDOT: PSS patterning technology, and study the influence about the introduction of structure on the photoelectric properties of the devices. At the same time, in order to solve the problems of the templates which is expensive in nano-imprinting, we have made a variety of structures by a single template based on the nano-imprinting and got more PDMS soft template for PEDOT:PSS stamping experiments. Experiments of concrete work is divided into the following three aspects:The preparation of Varieties of PMMA structures by single template: In order to get much more patterns by single grating template, firstly, we get one-dimensional PMMA grating by stardard thermal imprinting, and then peel and change the angle of templates in the secongd imprint process. Two dimensional diamond structures with regular morphology are achieved by controling the process temperature, pressure and the rotation angle of the template. In addition, after the first imprinting, we use a flat wafer to do the second imprinting. The line width of the grating structure is gradually widened with the increase of imprinting time. Experiments show that if the template does not fit tightly with the sample in the second plate embossing process, the PMMA grating structures will be distorted, and the amount of distortion is correlation with the temperature.Patterned PEDOT:PSS preparation by nanoimprinting lithograph combine with RIE and its application in QLED: Using nano-imprinting lithograph to realize of PEDOT: PSS pattern preparation, and the precise controlling of the structure height is achieved by reactive ion etching. Then the patterned PEDOT:PSS is introduced into the green QLED device, the experimental results show that electrically spectrum peak position of the device does not change along with the introduction of patterned PEDOT:PSS, and the maximum brightness of green QLED device is increased from 12760 cd/m2 to 16030 cd/m2, 25% better than the standard device, and the maximum current efficiency is increased from 4.19 cd/A to 6.74 cd/A, improved by 60%. The maximum brightness of the red QLED device is increased from 12610 cd/m2 to 17810 cd/m2, and its maximum power efficiency is increased from 1.38 cd/A to 3.82 cd/A. The simulation results accord with the experimental results.Patterned PEDOT:PSS/glycerol structure and its application in QLED: Due to that PEDOT: PSS does not have obvious glass transition temperature and the viscosity is to large, we use glycerol as the plasticizer added to the PEDOT:PSS aqueous solution, so that the PEDOT:PSS film has certain plasticity after spin coating, which promptes PEDOT: PSS/glycerol mixed film can be patterned by low temperture imprinting process. In detail, we discuss the glycerol doping amount, embossing pressure and post annealing effects on the morphology of PEDOT:PSS structure. Then, we introduce a patterned G-PEDOT:PSS grating structure with 750 nm period into the green QLED device, the results show that the maximum brightness is 68400 cd/m2 and the maximum current efficiency is 15.72 cd/A, under the same conditions, the maximum brightness of standard device is 64000 cd/m2, the maximum current efficiency is 15.78 cd/A.