【作者】 刘默；

【导师】 谢文法；

【作者基本信息】 吉林大学 ， 集成电路工程， 2011， 硕士

【摘要】 1963年,Pope等首次观察到了蒽的电致发光,此后,有机电致发光这一新技术逐渐进入了科学家的视野。经过近三十年的发展,有机电致发光器件已经在照明和显示上得到了一定程度的应用。与其他的照明和显示器件相比,OLED为冷光源,即在发光的过程中不会主动发热;可实现全固态显示,体积小,抗震性好;响应速度快,主动发光,视角宽,可实现柔性显示等优点,此外,由于环境温度对器件性能的影响不大,使得OLED产品可以在很多特殊的环境中工作。诸多优点,使得有机电致发光器件在照明和显示的市场中具有十分广阔的前景。但迄今为止,OLED器件仍未能实现普及化应用,其中,器件的效率是制约OLED普及化的重要原因。因此,本论文主要探讨了提高光取出效率的方法,对目前常用的提高光取出的方法进行总结,并通过实验,探讨了干涉作用以及微透镜对器件光取出效率的影响。目前,对于如何提高器件的光取出效率,科研人员已经提出了很多行之有效的方法。比如适当增大有机层与金属电极之间的距离来减少表面等离子模式对器件光取出效率的影响。在减少波导模式方面,许多科研人员采用在基板和ITO/有机层之间添加特殊结构的方法,例如在其间添加一些微结构,如二维光子晶体,周期性管状氧化铝,金纳米线,以及一些低折射率的网格结构,都可以有有效地将束缚在ITO/有机层中的光耦合出来。在减少基板模式方面,研究人员多采用在基板背面制作一些特殊结构的方法,如在基板背面添加不同形状不同尺寸的微透镜,贴附散射膜,利用喷砂(sand-blasting)的方法将其表面粗化,或是添加导光板,亦或贴附增透膜,这些方法都可以增大光有基板到空气的临界角,从而提高光耦合输出效率。在实验中,我们首先研究干涉作用对器件光耦合输出效率的影响。分别制作了结构为ITO/NPB/Alq3/LiF/Al的结构,首先固定NPB的厚度为50nm,使得Alq3的厚度分别为10nm,20nm,30nm,40nm,50nm,60nm,70nm,80nm,90nm,100nm;之后首先固定Alq3的厚度为50nm,使得NPB的厚度分别为10nm,20nm,30nm,40nm,50nm,60nm,70nm,80nm,90nm,100nm,利用这两个结构,来研究厚度对光取出效率的影响,即干涉作用对器件光取出效率的影响。同时,在不考虑电学特性的情况下,还用软件模拟了器件的光学特性,并将之与实验结果做对比。结果表明,两组结构的结果基本相同,当厚度较小时,器件的亮度较低,这种结果主要是由于,发光层与金属阴极的距离较近,使得表面等离子体模式对器件的影响比较严重;随着厚度的增加,此模式对器件的影响逐渐降低,器件的亮度也逐渐增大;而当器件的厚度进一步增加时,由于吸收,全反射等过程造成的损失又会进一步增大,使得器件的亮度再一次出现了下降的趋势,由此可以看出,Alq3和NPB对于器件光耦合输出效率的最佳厚度均为70nm。此后,我们又研究了微透镜对器件的影响。首先利用3D-FDTD方法对器件进行光学模拟,粗略的讨论了半球形微透镜的尺寸以及填充因子等因素对器件的影响,继而制作了红,黄,蓝三种光色的器件,并在基板背面贴附聚合物微透镜。结果表明,贴附微透镜后,器件的光耦合输出效率均有增加,但对于不同光色的器件,光耦合输出效率增加的程度不同,添加微透镜后,红光器件的亮度增加了80%,黄光器件的亮度增加了53%,蓝光器件的亮度增加了15%。更多还原

【Abstract】 In 1963,since Pope and his mates observed the electroluminescence of anthracene for the first time, Organic Light-Emitting Diodes ,as a new kind of technology, have entered into the scientist’s view.After almost three decades of development,organic light emitting devices have obtain application in a certain extent.Comparing with the traditional lighting and display devices, OLEDs possess a lot of advantages such as ultrathin, light weight,wide viewing angle,fast response and so on.In addition,other than traditional devices,OLED is cold light source, that is, in light of the process will not take the initiative to give out heat.All these advantages lead the OLEDs a very broad market prospects.But so far,OLEDs still can’t achieve universal access to applications ,the most important reason is its low efficiency.Therefore,in this paper,we will mainly summarize the methods of improving the light extraction efficiency of the devices which are commonly used around the world.Then we explore the role of interference and micro-lens played on the light extraction efficiency of the devices we used in the experiments in order to find an available way to improve the light extraction efficiency of OLEDs.Until now,there has been a lot of ways to improve the light extraction efficiency such as widening the distance between organic layers and the cathode in order to diminish the effect of surface plasma mode.Add some micro-structures,for instance, photonic crystal,periodic tubular aluminum oxide,gold nanowires,grid structure of low refraction,and so on,to decrease the effect of waveguide mode.Making some special structures on the back of the substrate,such as microlens with different shapes and sizes,anti-reflection film,light guide plate and so on,all the methods above can lead a increase of critical angle so that to out-coupling the light bounded in the substrate.In the experiment, we first study the varying light extraction efficiency caused by the effect of interference.The structure we used in the experiment is :ITO/NPB/Alq3/LiF/Al.First,we fix the thickness of NPB as 50nm,making the thickness of Alq3 to vary from 10nm to 100nm,increasing 10nm at a time.And then,fix the thickness of Alq3 as 50nm,making the thickness of NPB to vary from 10nm to 100nm,increasing 10nm at a time as well.In addition,we still make the simulation of the devices using microcavity theory which only take the effect of interference in account (without considering the electrical properties of the situation).By comparing this two kind of results,we found that when the varying layers are thin,the brightness is low,that is due to the effect of the surface plasmon mode,the lower the distance between the light-emitting layer and the cathode is,the greater the effect of the surface plasmon mode is.As it gets thicker,the brightness increasing gradually,for the effect of the surface plasmon mode becomes smaller.However,as it is too thicker,the brightness of the device appears on a downward trend again,for at this time,the effect caused by absorption and total reflection become stronger.And at last,we found that the optimal thickness of NPB and Alq3 for the best light out-coupled efficiency is 70nm.Since then, we have studied the impact of micro-lens on the device.We first evaluate the impact of the dimensions and packing factor of hemispheric microlens,using 3D-FDTD to simulate its photometric characteristics,and then make components of three different colors: red, yellow, and blue, and attached the microlens to the back of the substrates.The result showed that the efficiency of all the devices after attaching the microlens increased in a certain extent.For the blue components,it increased by 15%, for the yellow ones,it increased by 53% ,and 80% for the red ones.更多还原