Modification of ITO anodes with self-assembled monolayers for enhancing hole injection in OLEDs
Modification of ITO anodes with self-assembled monolayers for enhancing hole injection in OLEDs
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DOI：
10.1063/1.5086800
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发表时间：
2019-04-15
影响因子：
4
通讯作者：
Li, Xianggao
中科院分区：
文献类型：
--
作者：
An, Dong;Liu, Hongli;Li, Xianggao
提高载流子注入效率是提高有机电致发光器件性能的重要途径。在这项工作中，自组装单分子膜（SAMs）形成的铟锡氧化物（ITO）阳极与不同的芳香族羧酸。研究了改性剂的分子结构与改性效果的关系。通过X射线光电子能谱法验证了单层的存在。水接触角测试表明，ITO经SAM改性后表面能降低，有利于在ITO上获得平整的有机功能材料薄膜。另外，紫外光电子能谱数据表明，不同分子修饰的SAM-ITO的功函数都有不同程度的提高。因此，我们设计了一种无空穴注入层（HIL）器件，其结构为ITO/SAMs/α-萘苯基联苯二胺（NPB）（25 nm）/三（8-羟基喹啉）铝（III）（Alq（3））（60 nm）/LiF（1 nm）/Al（100 nm），以探索SAMs对OLED的影响。OLED性能显示，9 H-咔唑-2-羧酸（CzCA）的自组装膜有助于器件获得上级的发光性能，其开启电压为2.6V，最大亮度为30 418 cd.m（-2）。为了研究SAM分子的作用机理，采用Gaussian 09软件计算了SAM分子的最高占据轨道（HOMO）等信息。结果表明，CzCA的HOMO呈现出一种特殊的“通带”，有利于空穴的输运。当SAM分子的HOMO处于有利于空穴输运的形状时，将有利于空穴注入，从而大大提高OLED的性能。由AIP Publishing授权出版。
Increasing carrier injection efficiency is an important way to improve the performance of organic light-emitting diodes (OLEDs). In this work, self-assembled monolayers (SAMs) were formed on indium tin oxide (ITO) anodes with different aromatic carboxylic acids. The relationship between the molecular structure and its effect on modification was investigated. The presence of monolayers was verified by X-ray photoelectron spectroscopy. Water contact angle tests show that the surface energy of ITO has decreased after SAM modification which is beneficial to obtain a flat film of organic functional materials on ITO. In addition, the data of ultraviolet photoelectron spectroscopy reveal that the work function of SAM-ITO with different molecules modified has increased to varying degrees. Therefore, a no-hole injection layer (HIL) device whose structure is ITO/SAMs/alpha-naphthyphenylbiphenyldiamine (NPB) (25 nm)/tris(8-hydroxyquindino) aluminum (III) (Alq(3)) (60 nm)/LiF (1 nm)/Al (100 nm) was designed to explore the impact of SAMs on OLEDs. OLED performance shows SAMs of 9H-carbazole-2-carboxylic acid (CzCA) facilitating the device to obtain superior luminescence performance, with a turn-on voltage of 2.6V and a maximum luminance of 30 418 cd.m(-2). In order to study the mechanism, the highest occupied molecular orbital (HOMO) and other information of SAM molecules were calculated by Gaussian 09. According to the result, the HOMO of CzCA appears as a special "through-band," which is beneficial to the hole transport. It is considered that when the HOMO of the SAM molecule is in a shape favorable for hole transport, hole injection will be facilitated and the performance of the OLEDs will be improved greatly. Published under license by AIP Publishing.