Surface analysis on organic light emitting diodes

The main theme of this work is the application of various surface analysis techniques, including ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and atomic force microscopy (AFM), to the study of several issues related to the operating mechanisms of organic light emitting devices (OLEDs). Particular attention is paid to three areas: (1) the electronic properties and injection barrier at the organic/electrode interface; (2) the stability of organic thin films exposed to various environments; and, (3) the influence of processing parameters on the electronic and surface properties of organic thin films. Each of these topics is summarized in the following paragraphs. Properties of N’-bis-(1-naphthyl)-N,N’-diphenyl-1 ,1′-biphenyl-4,4′-diamine (NPB)/indium thin oxide (ITO) interface after different surface treatments were studied using UPS and AES. IT0 treated in situ by oxygen plasma possessed a work function of 5.2 eV and the NPB/ITO interface formed from this showed a hole injection barrier 0.5 eV lower than that of the untreated ITO. Insertion of an ultrathin SiO2 layer between the NPB and the ITO resulted in a similar reduction of the injection barrier. This improved hole injection favors the efficient operation of OLEDs, as manifested by the decreased operating voltage…

Author: Cheng, Lai-fung

Source: City University of Hong Kong

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