Oxidative Jet Deposition of Polythiophenes
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Oxidative Jet Deposition of Polythiophenes A. Davison Gilpin and F. James Boerio Department of Chemical and Materials Engineering University of Cincinnati, Cincinnati, OH 45221-0012, USA ABSTRACT An oxidative jet deposition process was used to deposit films of polythiophenes. The oxidative jet is created using two different methods, an ozone jet or a plasma jet. An ozone jet is created by forcing a gas mixture containing oxygen through a corona-discharge apparatus. A plasma jet is created by forcing an ionization gas through a radio-frequency plasma chamber. Polymerization and film deposition was achieved by rastering the jet over a substrate while a monomer was injected into the oxidative jet. The injected monomers include thiophene, 2methylthiophene, 3-methylthiophene, and 3,4-ethylenedioxythiophene (EDOT). The resulting films were studied with Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). FTIR spectra of the jet deposited films were characteristic of undoped poly(3,4-ethylenedioxythiophene) PEDOT. FTIR spectra showed that parameter optimized plasma jet deposited films contained less overoxidation in the form of hydroxyl and carbonyl groups than films deposited through the ozone jet process. The fabrication of organic electronics could be improved by this technology because a jet process allows for inline processing. Inline processing offers practical industrial advantages over the batch process methods currently used for depositing films of polythiophenes. INTRODUCTION PEDOT is a conductive polymer with optoelectronic properties suitable for use in the fabrication of organic electronic devices.1 Figure 1 shows the chemical structure of PEDOT. A plasma jet is formed by injecting an ionization gas into a concentrically confined glow discharge. Plasma jets exhibit the temperature range, charge-particle density, and reactive specie concentration characteristic of glow discharge plasmas formed in vacuum.2 Other investigations have shown that injecting a monomer into a plasma jet can lead to polymerization and subsequent film deposition.3 Ozone is a component of air plasmas and its ability to function as a polymerization agent independent of the other components of the plasma was investigated in this work. Ozone’s ability to polymerize EDOT was tested both in both jet deposition and solution environments.
Figure 1. The chemical structure of PEDOT. The motivation behind this work was to investigate new deposition routes for polythiophenes, with special emphasis on the industrially interesting PEDOT. Jet deposition is a scalable, open-air process amenable to inline processing. Therefore plasma jet deposited PEDOT (PJD-PEDOT) or ozone jet deposited PEDOT (OJ-PEDOT) could be ideal for industrial deposition of PEDOT. EXPERIMENT Plasma deposition was performed using a single rotary plasma jet (RD1004/FG1001, Plasmatreat North America Inc., Mississauga, ON, Canada). The rotary action was disabled for this work. EDOT monomer (Sigma-Aldrich C
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