以聚乙烯亚胺作为电子注入层的有机发光器件

发布时间：2018-06-28 01:44

本文选题：有机发光器件 + 电子注入层　；参考：《西南大学》2015年硕士论文

【摘要】：有机发光二极管(OLED)具有自主发光、广视角、高效率、低功耗、可用于柔性显示等特性,被认为是下一代显示技术最重要的技术之一,在OLED器件中,通常采用低功函数金属如Ca和Ba来提高电子的注入效率,然而这些低功函数金属对空气中的水分和氧气十分敏感,阴极金属的失效将严重地影响器件的正常工作和驱动稳定性。研究引入了金属氧化物如ZnO和TiO2作为电子注入层或通过对ITO进行修饰来制备倒置结构以解决这个问题。然而,金属氧化物到有机发光材料之间存在着很大的电子注入势垒。本论文通过加入聚乙烯亚胺(PEIE)修饰层来提高电子的注入效率。论文主要的研究工作包括以下几个方面：(1)在ITO或ITO/ZnO和发光层MEH-PPV层之间加入PEIE层有效地提高了器件发光效率。此外,在发光层与金属Al之间加入PEIE层使器件的发光效率增加了50倍。加有PEIE层的单电子器件的电流密度比未加PEIE层的高出5-10倍,由此表明PEIE层能够有效地改善了器件的电子注入能力,提高器件的发光效率。为了探究电子注入效率改善的机制,我们通过紫外线光电子能谱和X-射线光电子能谱法测量了PEIE/Al和ZnO/PEIE样品的功函数,发现在PEIE的修饰下ZnO和Al的功函数分别被降低了1.2 eV和1.0 eV,功函数的降低主要来源于界面偶极子层的形成。X射线光电子能谱的测量结果表明中性胺是降低功函数的主要原因。(2)为了探究从ZnO/PEIE到具有不同最低未占有轨道(LUMO)能级的发光材料的电子注入效率,我们研究了使用PF-TBT、SY和PFA分别作为发光层的有机-无机复合发光器件,其LUMO能级分别为-3.6、-2.7、-2.1 eV。这些有机-无机复合器件的发光效率与使用PEDOT:PSS和CsF作为空穴和电子注入层的传统结构器件的发光效率相似,由此表明从ZnO/PEIE到发光聚合物层的电子注入势垒非常小。所以,对于LUMO能级差别较大的发光聚合物而言,PEIE都可以作为有效的电子注入层。(3)相比于普遍采用的Cs2CO3电子注入层,PEIE具有与有机材料接近的表面能并可形成均匀的薄膜,对有机发光层特别是包含磷光材料的发光层的形貌影响较小。因此,我们探究了基于溶液加工小分子材料发光层和PEIE电子注入层的有机-无机复合发光器件的发光特性。发光器件的最高发光效率是87.6 cd A-1,在亮度为1000 cd m-2时,器件的外量子效率为20.9%。该器件的发光效率为以往报道的基于ZnO:Cs2CO3电子注入层的发光器件的4倍,这归因于PEIE具有优良的电子注入能力和空穴/激子阻挡能力,特别是PEIE与发光层之间可形成良好界面。
[Abstract]:Organic light emitting diodes (OLEDs) are considered as one of the most important technologies in the next generation of display technology, because they have the characteristics of independent luminescence, wide viewing angle, high efficiency, low power consumption, and can be used for flexible display. Low power function metals such as Ca and Ba are usually used to improve the efficiency of electron injection. However, these low power function metals are very sensitive to air moisture and oxygen, and the failure of cathode metals will seriously affect the normal operation and driving stability of the devices. Metal oxides such as ZnO and TiO2 were introduced as the electron implantation layer or modified by ITO to prepare the inverted structure to solve this problem. However, there are large electron injection barriers between metal oxides and organic luminescent materials. In this paper, the electron injection efficiency is improved by adding polyethylene imine (PEIE) modified layer. The main research work includes the following aspects: (1) adding PEIE layer between ITO / ITO / ZnO and MEH-PPV layer can effectively improve the luminescence efficiency of the device. In addition, the addition of PEIE layer between the luminescent layer and Al increases the luminescence efficiency by 50 times. The current density of single electron device with PEIE layer is 5-10 times higher than that without PEIE layer, which shows that PEIE layer can effectively improve the electron injection ability of the device and improve the luminescence efficiency of the device. In order to explore the mechanism of improving electron injection efficiency, we measured the work functions of PEIE-Al and ZnO / PEIE samples by ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy. It was found that the work functions of ZnO and Al were decreased by 1.2 EV and 1.0 EV respectively under the modification of PEIE. The decrease of work function was mainly due to the formation of interfacial dipole layer. The results of X-ray photoelectron spectroscopy showed that neutral amine was the reducing work function. (2) in order to explore the electron injection efficiency from ZnO / PEIE to luminescent materials with different lowest non-occupied orbital (LUMO) energy levels, Using PF-TBTSY and PFA as luminescent layers, the LUMO levels of organic-inorganic composite luminescent devices are studied. The LUMO levels are -3.6 ~ 2.7U ~ (-2.1) EV, respectively. The luminescence efficiency of these organic-inorganic composite devices is similar to that of conventional devices using PEDOT: PSS and CSF as hole and electron injection layers, which indicates that the electron injection barrier from ZnO / PEIE to luminescent polymer layer is very small. Therefore, PEIE can be used as an effective electron injection layer for luminescent polymers with different LUMO energy levels. (3) compared with the widely used Cs2CO3 electron implantation layer, PEIE has surface energy close to that of organic materials and can form a uniform film. It has little effect on the morphology of the organic luminescent layer, especially the luminescent layer containing phosphorescent material. Therefore, we investigated the luminescence characteristics of organic-inorganic composite luminescent devices based on solution fabrication of small molecular materials and PEIE electron implantation layers. The maximum luminescence efficiency of the device is 87.6 CD A-1. When the luminance is 1000 CD m-2, the external quantum efficiency of the device is 20.9. The luminescence efficiency of the device is 4 times higher than that of the previously reported device based on ZnO: Cs2CO3, which is attributed to PEIE's excellent electron injection ability and hole / exciton blocking ability, especially the good interface between PEIE and the luminescent layer.
【学位授予单位】：西南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN383.1

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