【作者】 谢国华；

【导师】 全宝富； 赵毅；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2011， 博士

【摘要】 有机电致发光器件具有低工作电压、高亮度、高效率、高对比度、厚度薄、重量轻、可视视角宽、工作温度范围宽、工艺简单、可制作在柔性衬底上等诸多优点,在新一代的显示和照明产品上有着广泛的应用前景。经过二十多年的快速发展,该类器件已经从单纯基础研究,逐渐转变到了大力开发产品的阶段。为了适应下一代平板显示器和白光照明面板的长寿命、高效率、低成本的开发要求,需要对有机电致发光器件的性能进行更深层次的优化。本论文从改善有机电致发光器件的性能以满足实用化需求的角度出发,探索制备低驱动电压发光器件的方法,满足发光器件与有源显示驱动电路工作条件和制备工艺相兼容的迫切要求；研究载流子传输和激子限制作用对白光有机电致发光器件的影响,分别设计和制备低驱动电压、高效率的底发射和顶发射结构的白光有机电致发光器件。主要研究成果包括以下几个方面：1.结合有机半导体p型电学掺杂的结构,分析不同电子传输层结构的电子传输和空穴阻挡能力对底发射有机电致发光器件的驱动电压、发光效率等性能的影响,’研究荧光染料C545T在主体材料Alq3中的载流子陷阱行为,结合软件模拟计算,得出了不同弱微腔结构中发光层的偶极子分布的简化模型。同时利用p型电学掺杂层厚度变化对器件的电学特性不敏感的特性,优化了适合有源显示器的发光器件结构,将低驱动电压的底发射有机电致发光器件成功地移植到基于低温多晶硅薄膜晶体管技术、分辨率为128×96×3的有源显示发光屏上,实现全屏的均匀发光。2.利用前面得出的偶极子分布的模型,对顶发射结构的有机电致发光器件的不同光学模式分布进行模拟,从应用到直视型器件的角度出发,最大程度地提高正向光耦合输出效率,结合p型电学掺杂技术,利用高效的荧光染料,制备了应用于有机电致发光微显示器的低工作电压(4.0和4.9 V下的亮度分别达到2500和10000 cd/rn2)、高效率(1000cd/m2亮度下的功率效率为28.8 lm/W)的单色荧光顶发射器件,同时研究了有机：无机电学掺杂层的热稳定性。从器件集成个工艺整合的角度出发,研究芯片表面Ag金属层的形貌对微显示器性能的影响,结合上述研究成果和相关的微电子电路技术,我们成功地开发了我国第一款QVGA硅上有机微显示器原型样机。3.通过在蓝色(mCP:FIrpic)和黄色(mCP:(F-BT)2Ir(acac))磷光发光层中间插入不同界面层的方法,仔细研究了白色有机电致发光器件中发光层内部的载流子传输特性和激子扩散行为,分析了p型导电的mCP、n型导电BPhen、双极传输型的mCP:BPhen等三种中间界面层结构对器件工作电压、发光特性的影响,比较NPB/mCP和Ir(ppz)3两种三线态激子阻挡结构的激子扩散、器件工作电压和发光特性的影响,结合p型电学掺杂技术制备了可用于白光照明的低驱动电压(4V下的亮度达到1333cd/m2)、高效率(100cd/m2亮度下的功率效率约为40lm/W)的结构简单的全磷光器件。4.从工艺实现路线和生产成本的角度考量,详细讨论了Cu电极在研制全彩色硅上有机微显示器应用上的必要性和可行性。在底发射白光器件结构设计的基础上,利用软件模拟的方法,优化顶发射白光器件的结构,分析顶发射结构中顶部光学覆盖层与白光耦合输出效率、光谱特性和对比度的关系。首次报道了基于Cu电极的低驱动电压(4.4V下的亮度达到1000cd/m2)、高效率(10mA/cm2的电流密度下,电流效率达到27.7cd/A,功率效率达到17.6lm/W)的顶发射白光有机电致发光器件。通过采用有机：无机p型电学掺杂技术,结合软件进行理论模拟,优化器件结构设计,在本论文中提供了解决有机电致发光器件在有源显示和白光照明应用方面的一些方法,同时对有机电致发光器件的光学特性和电学特性分别进行了细致的分析。本论文的主要创新点包括：1)合理地利用了稳定而且低成本的有机：无机(m-MTDATA:MoOx) p型电学掺杂技术,研究制备低驱动电压、高效率的有机电致发光器件的方法；2)通过实验对载流子阻挡和陷阱作用的表征,结合对有机电致发光器件的光学模式分布规律的模拟,得出对应于不同载流子阻挡和陷阱结构的偶极子分布规律,该结果对我们优化器件发光耦合输出特性有着重要的指导意义；3)将上述研究成果分别成功地应用到基于低温多晶硅薄膜晶体管技术的底发射结构有源驱动显示屏和我国第一款单色QVGA有机微显示器的研制中；4)采用简单的mCP、BPhen、mCP:BPhen等中间界面层的结构,用实验和理论相结合的方法揭示了互补双发光层白光器件内部的光子、载流子和激子行为随不同界面层变化的特点；5)首次报道了基于Cu电极的低驱动电压、高效率的顶发射白光有机电致发光器件,研究了m-MTDATA光学覆盖层对顶发射白光器件的耦合输出效率和光谱分布特性的影响,为下一步开发全彩色、低成本、高稳定性的有机微显示器提供了一种可靠的方案。更多还原

【Abstract】 Organic light-emitting diodes (OLEDs) have great potential applications in the next generation flat panel displays and solid-state lighting products, because of their advantages of low driving voltage, high luminance, high efficiency, high contrast, thinness, low weight, wide viewing angle, wide range of operating temperature, simple process, and flexibility. Over the last two decades, the activities on OLEDs turn to focus on the development of the commercial products, derived from the monotonously fundamental research. To further satisfy the requirements of longevity, high efficiency and low-cost, much more effort should be made on the further improvements of OLEDs’performances.In this contribution, the solutions to fabricate OLEDs with low driving voltage are suggested, in view of improving the performances of OLEDs for practical use and integrating OLEDs on active matrix circuits based substrates with compatible process. Both bottom-emitting white OLEDs (BEWOLEDs) and top-emitting white OLEDs (TEWOLEDs) with low driving voltage and high efficiencies are demonstrated. Some mechanisms of the influences of charge carriers and excitons on the performance of white OLEDs (WOLEDs) are revealed. The main achievements involved in this dissertation are listed as follows.1. A novel p-type electrical doping of organic semiconductor is introduced. The influences of electron transporting materials with different ability of electron transportation and hole blocking on the performances of OLED are investigated. The behavior of charge trapping of C545T in Alq3 is probed. Simple models of the distribution of the emissive dipoles in different structures with weak microcavity are derived by analyzing the experimental and simulated results. As the current-voltage characteristics of OLEDs are not sensitive to highly conductive doped hole injecting layer,the thicknesses of p-doping layer are optimized for 128x96x3 active matrix displays with uniform and full-screen emission, which are based on low-temperature polysilicon thin film transistors.2. Based on the dipole model mention above, the optical mode contributions in top-emitting OLEDs (TEOLEDs) are calculated. The forward emission is maximized for the devices used in the near-eye circumstance. Low driving voltage (2500 and 10000 cd/m2 achieved at 4.0 and 4.9 V, respectively) and highly efficient (28.8 1m/W at the luminance level of 1000 cd/m2) TEOLED is demonstrated with an efficient fluorescent dye and a p-doping strategy which is also highly thermal-stable. Implemented with the optimized TEOLED structure and an improved Ag chemical mechanical polishing process, a first prototype of monochromatic QVGA OLED microdisplay in China is also demonstrated.3. The characteristics of charge carriers and exciton in WOLEDs are probed by inserting the interlayers between the two emissive zones based on two complementary blue ((mCP:FIrpic) and yellow (mCP:(F-BT)2Ir(acac)) emitters. The dependences of the driving voltages and efficiencies on the p-type conductive mCP, n-type conductive BPhen and ambipolar mixed mCP:BPhen interlayers are revealed. The NPB/mCP structure is replaced by Ir(ppz)3 to enhance the confinement of the triplets in the emitting layer. With a p-doping hole injecting layer, phosphorescent WOLED for lighting with simple architecture exhibits low driving voltage (1333 cd/m2 at 4 V) and high power efficiency (40 lm/W achieved at the luminance level of 100 cd/m2).4. Both the necessity and feasibility of Cu contact in view of process compatibility and manufacturing cost for full color OLED microdisplays are under deliberate consideration. The simulation of TEWOLEDs sheds light on the influence of the capping layer on white light emission, the out-coupling efficiency, and contrast ratio in top-emitting structure. A first reported Cu-based TEWOLED with low driving voltage (1000 cd/m2 at 4.4 V) and high efficiencies (27.7 cd/A and 17.6 Im/W at 10 mA/cm2, respectively) is demonstrated.An air-stable organic:inorganic p-doping structure is introduced to fabricate low driving OLEDs. The software simulation simplifies the design of highly efficient OLEDs. Some solutions to the applications of OLEDs in active matrix displays and lighting are suggested in this contribution. Detailed analyses of the optical and electrical characteristics of OLEDs with the structures used in this dissertation are presented. The innovations imbedded here are listed as follows:1) Solutions towards low driving voltage and highly efficient organic light-emittin diodes are presented.2) The carrier blocking layers and charge trapping architecture are introduced to characterize the distribution of emissive dipoles in OLEDs with single emitting layer. 3) Based on the above mentioned technique, especially the air-stable p-doping strategy, active matrix OLEDs implemented in the substrates with low temperature polysilicon thin film transistors and a first prototype of QVGA OLED microdisplay in China are demonstrated, respectively.4) The interlayers between the two emitting layer in WOLEDs are introduced to tailor the performances. The behaviors of the photons, charge carriers and excitons in such devices are also investigated.5) It is the first time, to the best of our knowledge, Cu contact used for low driving voltage and highly efficient TEWOLED is presented. The role of a capping layer on top of TEWOLED is theoretically and experimentally investigated.更多还原