Polymer Electrodes for Flexible Organic Light-Emitting Devices
- PDF / 507,732 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 109 Downloads / 236 Views
I12.5.1
POLYMER ELECTRODES FOR FLEXIBLE ORGANIC LIGHT-EMITTING DEVICES Woohong Kim,1 Leonidas C. Palilis,1 Antti J. Mäkinen,1 Heungsoo Kim,1 Manabu Uchida,2 and Zakya H. Kafafi1 1 2
Naval Research Laboratory, Washington D.C. 20375 Chisso Corporation, 5-1 Ookawa Kanazawa, Yokohama, Kanagawa 236-8605, JAPAN
ABSTRACT We report a high luminance and low operating voltage molecular organic light-emitting diode (MOLED) using a conducting polymer hole-injecting electrode (anode) on a plastic substrate. A dramatic improvement in the rectification ratio is observed upon the insertion of a buffer layer between the conducting polymer anode and the organic hole-transporting layer (HTL). Micro-shorts leading to a leakage current caused by the non-uniformity of the polymer film are greatly reduced. Atomic force microscope (AFM) images show a much smoother surface of the polymer anode/buffer layer relative to that of the bare polymer film. A slight increase (0.3eV ± 0.2eV) in the work function of the polymer anode upon the addition of the buffer layer is also measured. A simple method of patterning the conducting polymer electrode on various substrates including plastics is also reported. This approach conveniently provides finely patterned conducting polymer films with µm resolution while maintaining their intrinsic electrical and optical properties such as the surface sheet resistance and the optical transmittance. INTRODUCTION Most opto-electronic devices such as liquid crystal displays (LCDs) and organic lightemitting diodes (OLEDs) require electrically conductive and transparent electrodes. Typically, indium tin oxide (ITO) is used as the transparent electrode material since it is highly conductive and transparent in the visible region (400~800nm). ITO can be vacuum vapor-deposited, sputtered, or pulsed laser deposited (PLD) onto glass or plastic substrates [1-7]. ITO films with a surface resistance of less than 100 Ohms/sq and a high transparency of > 90% can be easily obtained using any of these deposition methods. However, the production of ITO must be carried out under vacuum and is very costly. Also, an additional multi-step photolithographic process is necessary to provide the substrate with the desired pattern geometry for the specific application. The photolithographic patterning method employs various chemicals including cleaning solutions, photoresist/solvent, acidic etchant, developer and stripper, most of which are environmentally toxic and hazardous. Recently, conducting polymers have attracted a great deal of attention as a potential replacement for ITO in many electronic and opto-electronic devices especially for those using flexible substrates. This is primarily due to their good mechanical strength and, maintaining their electrical and optical properties upon substrate flexing and bending [8]. Among them, poly(3,4ethylenedioxy-thiophene)-polystyrenesulphonate (PEDOT:PSS), first introduced in the past decade by Bayer AG Germany, is the most widely used polymer in applications such as antistatic coating in ph
Data Loading...
