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Electrochromism and over-oxidation in conjugated polymers: Improved color switching and a novel patterning approach
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
2006 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

During the last 30 years a new research and technology field of organic electronic materials has grown thanks to a groundbreaking discovery made during the late 70’s. This new field is today a worldwide research effort focusing on exploring this new class of materials that also enable many new areas of electronics applications. In the organic electronics research field conducting organic molecules and polymers are synthesized and used in devices. The reason behind the success of conducting polymers is the flexibility to develop materials with new functionalities via clever chemical design and the possibility to use low-cost production techniques to manufacture devices.

This thesis reviews and describes different aspects of the organic electronics, here focusing on electrochromic displays; device improvements, the study of degradation and also patterning technology for rational manufacturing processing. The color contrast in electrochromic displays based on conjugated polymers was increased with approximately a factor of two by adding an extra electrochromic polymer. It was found that electrochemical over-oxidation (ECO) limits the flexibility in choosing desired electrochromic materials. ECO is one of the main degradation mechanisms in electrochromic displays. ECO is an efficient and fast process to permanently reduce the electronic conductivity in polythiophenes. From this, a novel patterning process was developed, in which the films of polythiophenes can be patterned through local and controlled deactivation of the conductivity. The ECO has been combined with different patterning tools to enable the use of existing printing tools for manufacturing. In combination with screen-printing, low-cost and high volume roll-to-roll patterning was demonstrated, while together with photolithography, patterning down to 2 µm can be achieved. Systematic studies have shown that conductivity contrasts beyond 107 can be achieved, which is enough for various simple electronic systems. To generate better understanding of the ECO phenomena the effect of pH on the over-oxidation characteristics was studied. The results suggest that a part of the mechanism for over-oxidation depends on the OH– concentration of the electrolyte used.

Place, publisher, year, edition, pages
Institutionen för teknik och naturvetenskap , 2006. , 31 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1237
Keyword [en]
Conjugated polymers, Over-oxidation, Patterning, Electrochromism, PEDOT:PSS
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:liu:diva-7478Local ID: LiU-TEK-LIC- 2006:17ISBN: 91-85497-34-7 (print)OAI: oai:DiVA.org:liu-7478DiVA: diva2:22484
Presentation
2006-03-02, TP2, Täppan, LiU Norrköping, Norrköping, 14:15 (English)
Opponent
Supervisors
Available from: 2006-10-04 Created: 2006-10-04 Last updated: 2017-02-03
List of papers
1. Patterning polythiophene films using electrochemical over-oxidation
Open this publication in new window or tab >>Patterning polythiophene films using electrochemical over-oxidation
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2005 (English)In: Smart materials and structures (Print), ISSN 0964-1726, E-ISSN 1361-665X, Vol. 14, N21-N25 p.Article in journal (Refereed) Published
Abstract [en]

Over-oxidative degradation of polythiophenes, which breaks the conjugation and destroys the electronic conductivity of the polymer, is well documented as a liability in these materials. We use this 'weakness', via controlled electrochemical over-oxidation, in a novel subtractive patterning technique compatible with high-speed reel-to-reel printing technology. We demonstrate the use of electrochemical over-oxidation to pattern PEDOT:PSS films via an x–y plotter, silk-screen and high-resolution photolithographic techniques, resulting in patterning down to a resolution of 2 µm and a conduction contrast between unpatterned and patterned areas of up to 108.

Place, publisher, year, edition, pages
IOP Elctronic Journals, 2005
Keyword
Not Available.
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-14024 (URN)10.1088/0964-1726/14/4/N03 (DOI)
Available from: 2008-11-12 Created: 2008-10-17 Last updated: 2017-12-13Bibliographically approved
2. Evaluation of active materials designed for use in printable electrochromic polymer displays
Open this publication in new window or tab >>Evaluation of active materials designed for use in printable electrochromic polymer displays
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2006 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 4, 2485-2492 p.Article in journal (Refereed) Published
Abstract [en]

In a step towards roll-to-roll production of polymer-based electrochromic displays on flexible substrates, nine thiophene-based polymers and copolymers designed to increase the contrast of displays based on poly(3,4-ethylenedioxythiophene)/poly(styrene-sulfonic acid) have been synthesized and evaluated with respect to their absorbance (contrast), switch speed, and ability to switch reversibly in a water-based electrolyte. The results of the evaluation, including cyclic voltammetry and optically visible absorption, provide a basis for understanding what an aqueous electrolyte electrochromic display requires in terms of oxidation potential and material stability, and the effect of chemical structure on the reversibility and speed of switching. © 2006 Elsevier B.V. All rights reserved.

Keyword
Electrochromic display; Conjugated polymers; Poly(3, 4-ethylenedioxythiophene)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-37443 (URN)10.1016/j.tsf.2006.07.149 (DOI)35830 (Local ID)35830 (Archive number)35830 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
3. The effect of pH on the elechtrochemical over-oxidation of PEDOT:PSS films
Open this publication in new window or tab >>The effect of pH on the elechtrochemical over-oxidation of PEDOT:PSS films
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2007 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 177, no 39-40, 3521-3527 p.Article in journal (Refereed) Published
Abstract [en]

Chemical degradation of conjugated polymers is one cause of material failures in polymer-based (opto)electronic devices, but can also be used as a technique for subtractive patterning of polymer films. When a large anodic potential is applied to the conducting polymer blend poly(3,4-ethylenedioxythiophene)-poly(4styrenesulfonate), PEDOT:PSS, an over-oxidation reaction occurs, altering its electrical conductivity. Here, we have studied the effect of pH on the electrochemical over-oxidation process of PEDOT in PEDOT:PSS. High pH is associated with a decrease of over-oxidation potential and an increase of resistivity in the resulting film. Vibrational spectroscopy and photoelectron spectroscopy measurements on over-oxidized PEDOT:PSS films indicate that the decrease in conductivity results from cleavage of the conjugation pathway accompanied by the formation of sulfone, carbonyl and carboxylic groups in the polymer chain.

Place, publisher, year, edition, pages
ScienceDirect, 2007
Keyword
Poly(3, 4-ethylenedioxythiophene), Degradation, Over-oxidation, XPS, FTIR, Conjugated polymer, Polythiophenes
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-14026 (URN)10.1016/j.ssi.2006.10.008 (DOI)
Available from: 2008-11-12 Created: 2008-10-17 Last updated: 2017-12-13Bibliographically approved

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