Analysis of the Injection Layer of Liq in Inverted OLEDs Using Atomic Force Microscopy and X-ray Photoelectron Spectroscopy
A comprehensive understanding of the electronic states of the surface and interface is meaningful for organic light-emitting devices (OLEDs). 8-Hydroxyquinolinolatolithium (Liq)/ indium-tin-oxide (ITO) thin film are analyzed using X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) is also applied to investigate the morphology of Liq/ITO film. The above-mentioned ITO is directly employed as cathode and Liq as electron injecting layer in inverted OLEDs. AFM observation indicated that the surface is complanate, the Liq growth is uniform and defects cover basically the surface of ITO. Furthermore, the number of pinholes is small. And what is more, the analysis of the sample surface and interface further verifies this result by using XPS. XPS results show, the core-levels of Li 1s, C1s, N1s, O1s, In 3d5/2, and Sn 3d5/2, spectra slightly shift towards lower binding energy with the increase of the sputtering time, which may be caused by the effect of oxygen, indium and tin in ITO diffusing into Liq layer. At the same time, Liq is found to have the ability of restraining the diffusion of chemical constituents from ITO to the electron transport layer, which is beneficial to the improvement of the performance and useful lifetime of the inverted OLEDs. Besides these, the single feature of the Li 1s peak becomes two peaks, indicating there is the interaction of Li atoms with ITO. This reaction has caused a chemical change in Liq, which also might be an important reason that Liq layer can enhance the injection of electron. Our experimental results support the assumption that free lithium released from Liq. These results may explain that Liq is very effctive to be used as an electron injection layer for inverted bottom-emission organic light-emitting diodes.
J.F.Li W.L.Chang F.J.Zhang
School of Physical Science and Technology Lanzhou University,Lanzhou 730000,China;School of Mathemat School of Mathematics,Physics & Software Engineering Lanzhou Jiaotong University,Lanzhou 730070,Chin School of Physical Science and Technology Lanzhou University,Lanzhou 730000,China
国际会议
Progress in Electromagnetics Research Symposium 2009(2009年电磁学研究新进展学术研讨会)(PIERS 2009)
北京
英文
1073-1078
2009-03-23（万方平台首次上网日期，不代表论文的发表时间）