【作者】 张帅；

【导师】 黄维； 陈淑芬；

【作者基本信息】 南京邮电大学 ， 光学工程（专业学位）， 2016， 硕士

【摘要】 有机发光器件(OLED)具有色彩鲜艳、对比度高、响应速度快、外形轻薄、效率高和机械灵活性等特点,在柔性显示、绿色显示和可穿戴便携显示等新一代显示技术领域表现出广阔的发展前景。然而目前基于ITO电极的OLED不耐弯折,无法实现良好的柔性显示,石墨烯具有良好的机械柔韧性和高透光性,可代替ITO实现机械性能良好的柔性OLED显示。不幸的是,由于石墨烯较低的功函数和较大的方阻,导致石墨烯OLED的效率还较低。在过去的几年里,人们通过改善石墨烯质量、结构官能化、掺杂等方法来提高石墨烯OLED性能。本工作发现了石墨烯OLED中存在的负微分电阻(NDR)/迟滞现象严重影响着器件的稳定性和发光性能。我们使用电流退火(在±5 V范围内往返扫描器件)的方式来抑制这些现象,提升了器件的发光效率。研究表明,NDR和迟滞现象分别来自于残留PMMA的空穴隧穿效应和有机材料中的陷阱,其中,低电压下石墨烯表面残留的PMMA导致大量空穴隧穿,进而产生了NDR现象。高电场产生的焦耳热使得PMMA附近温度上升到数百摄氏度,这些焦耳热能够让PMMA分解,进而有效去除NDR现象;而我们高压下电流的拟合结果表明,高压下的迟滞现象来源于有机材料的陷阱作用,经电流退火(往返扫描电流)后器件中的陷阱被填满,因此,高压下的迟滞现象也被有效抑制。本工作为进一步提升石墨烯OLED性能提供了新方法,这种方法与常规的减小方阻和提高功函数的方法结合,非常有助于获得高性能石墨烯有机发光器件。值得注意的是,本文基于黄光PO-01的石墨烯OLED亮度和效率分别超过60000 cd/m2和90 cd/A。更多还原

【Abstract】 Organic light-emitting diode(OLED) has shown wide application prospect in next-generation display technology including flexible, pollution- free and wearable portable displays due to its many advantages of rich colours, high contrast ratio, fast response volecity, light weight, high luminous efficiency and fine mechanical flexibility.Graphene is a very promising electrode material in flexible, stretchable displays and lighting applications. Employing graphene as electrodes can eliminate those drawbacks in ITO-based OLEDs and is compatible with current low-cost, mass- manufacturable and large-scale printing technology. Unfortunately, luminous efficiencies in most graphene OLEDs are still very limited due to low work function and large sheet resistance of graphene. In the past several years, the luminous efficiency in graphene-based OLEDs has been gradually improved via manufacturing a high-quality graphene with a low sheet resistance or modifying its surface with a high work function material.In this work, negative differential resistance(NDR)/hysteretic behaviors as important factors were observed to seriously affect emission stability and performances in graphene OLEDs. O ur results indicate that the NDR and the hysteresis are respectively originated from the hole tunneling induced by residual PMMA and traps in bulk organic materials, which can be removed via a current annealing approach, accompanied with a significant increase in luminous efficiency. Under a low voltage region residual PMMA covered on the surface of graphe ne results in part of voltage drop onto the ultrathin PMMA, thus generating a hole tunneling accompanied by N DR phenomenon. The large hole tunneling current passing through the conducting device, just like a current annealing process, generates Joule heating and significantly increases the sample temperature around residual PMMA to several hundred centigrades. This large Joule heating leads to the decomposition of PMMA. O ur calculation results indicate that the hysteresis phenomenon under a high voltage region is related to the traps in bulk organic materials and it can be removed after these traps are fully filled after several J-V scans.The work presented here offers a new approach for further device improvements, and the combination of this approach with previously reported methods of reducing sheet resistance and increasing work function will be very useful for fabricating high-performance graphene optoelectronic devices. Notably, the luminance and current efficiency of graphene O LED based on the Iridium(III)bis(4-phenylthieno[3,2-c]pyridinato-N,C2’)acetylacetonate(PO-01) yellow phosphor are as high as >60000 cd/m2 and >90 cd/A in this thesis.更多还原