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Acido-basic control of the thermoelectric properties of poly(3,4-ethylenedioxythiophene)tosylate (PEDOT-Tos) thin films
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Optoelectronics Group, Cavendish Laboratory, University of Cambridge, Cambridge, UK.
Linköping University, Department of Physics, Chemistry and Biology, Molecular Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0003-3899-4891
Linköping University, Department of Science and Technology. Linköping University, Faculty of Science & Engineering. University of South Australia, Mawson Institute, Mawson Lakes 5095, Australia.
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2015 (English)In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 3, p. 10616-10623Article in journal (Refereed) Published
Abstract [en]

PEDOT-Tos is one of the conducting polymers that displays the most promising thermoelectric properties. Until now, it has been utterly difficult to control all the synthesis parameters and the morphology governing the thermoelectric properties. To improve our understanding of this material, we study the variation in the thermoelectric properties by a simple acido-basic treatment. The emphasis of this study is to elucidate the chemical changes induced by acid (HCl) or base (NaOH) treatment in PEDOT-Tos thin films using various spectroscopic and structural techniques. We could identify changes in the nanoscale morphology due to anion exchange between tosylate and Cl- or OH-. But, we identified that changing the pH leads to a tuning of the oxidation level of the polymer, which can explain the changes in thermoelectric properties. Hence, a simple acid-base treatment allows finding the optimum for the power factor in PEDOT-Tos thin films.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2015. Vol. 3, p. 10616-10623
National Category
Polymer Chemistry Textile, Rubber and Polymeric Materials
Identifiers
URN: urn:nbn:se:liu:diva-121977DOI: 10.1039/C5TC01952DISI: 000363251600035OAI: oai:DiVA.org:liu-121977DiVA: diva2:860829
Note

Funding agencies: European Research Council (ERC) [307596]

Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2018-02-13Bibliographically approved
In thesis
1. Thermoelectric Devices with Electronic and Ionic Conducting Polymers
Open this publication in new window or tab >>Thermoelectric Devices with Electronic and Ionic Conducting Polymers
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The energy consumption in the world is continuously growing and the sources of energy are largely dominated by fossil fuels. However, the resources of oil, gas and coal are diminishing in capacity. Moreover the CO2 emissions arising from their combustion is a great concern because it induces climate changes that threaten our habitat. There is a dire need to look for alternative sources of energies and to minimize losses of energy in our surroundings. Heat engines and turbines typically running with fossil energy have efficiencies of about 35%, i.e. 65% of the energy is lost in the form of heat. Low temperature heat (<200 C) is almost always wasted in power plants, industries, automobiles and household appliances. This is a huge resource that can be directly converted to electricity through the concept of thermoelectricity. Major challenges for heat to electricity conversion include finding the abundant materials with efficient thermoelectric (TE) conversion that can be mass produced at low cost.

This thesis presents an investigation of the TE properties of electronic and ionic conducting polymers, as well as their implementation in thermoelectric devices. This is a journey from thin solid films on a substrate to wet and liquid media and towards bulk structures utilizing the same core concept of thermoelectricity. The TE device concepts introduced here are suitable for various heat sources i.e. continuous, intermittent and instantaneous. The thesis has three major parts as follows:

Conducting polymers (CPs) have been studied mainly as thin films. They have been synthesized in different ways and their properties have been compared to propose the most efficient amongst them for thermoelectricity. Simple methods of exposure to certain gases or liquids have been used to tune their TE properties and demonstrated its applications in thermoelectric generator (TEGs).

Ionic materials have also been studied as potential candidates for thermoelectricity. Polyelectrolytes constitute a special class of electrolytes with dissimilar sizes of ions; a polymeric ion and a small counter ion. The movement of the small sodium (Na+) cation under heat gradient was explored in wet films and in solution. Because the ions could not cross the electrolyte-electrode junction, we propose the idea of ionic thermoelectric supercapacitor (ITESC), suitable for intermittent heat source.

Nanofibrillated cellulose (NFC) has been used along with conducting polymers to realize the three dimensional conducting bulks as a TEG leg. NFC bulks were coated with conducting polymers as a first approach and later the mixture of (NFC & CP) was freeze-dried. The later approach resulted in mechanically flexible structures that were used as dual sensors for pressure and temperature based on the TE properties of the CP which can be utilized for electronic skin applications.

The thesis shows new ways of utilizing waste heat using polymeric materials and points to a sensory application area, broadening the horizons of thermoelectricity.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. p. 50
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1709
Keyword
Thermoelectricity, conducting polymers, thermoelectric devices
National Category
Physical Sciences Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-121982 (URN)978-91-7685-931-5 (ISBN)
Public defence
2015-11-12, Resuren (Pronova), Campus Norrköping, Norrköping, 10:00 (English)
Opponent
Supervisors
Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2017-02-03Bibliographically approved
2. Application of Vibrational Spectroscopy in Organic Electronics
Open this publication in new window or tab >>Application of Vibrational Spectroscopy in Organic Electronics
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The rapid technological developments enforce us to live in an increasingly electronic world, and the revolutionary usage of conjugated polymers in electronics in the late 1970s accelerated these developments, based on the unique characteristics of conjugated polymers, such as low cost, easy processing, mechanical flexibility, large-area application and compatibility with a variety of substrates. Organic electronic devices are commercially available in the form of, for example, solar cells, transistors, and organic light-emitting diode (OLED) displays. Scientists work on electroactive polymers to enhance their chemical, electrical and mechanical properties, to improve parameters such as charge carrier mobility and doping capacity, in order to reach acceptable efficiency and stability to fabricate organic electronic devices. A comprehensive understanding of the changes in chemical structure, in response to external factors such as applied potential and temperature gradients, which can disturb the chemical equilibrium of the constituent materials, and of the conduction mechanisms of the operating devices, can help to enhance the performance of organic electronics devices. Vibrational spectroscopy is a powerful analytical method for in-situ monitoring of such chemical or electrochemical reactions and associated structural changes of conjugated polymers in a working device.

In this thesis, Fourier-transform infrared (FTIR) spectroscopy has been used to study the structural changes in electroactive organic materials, in response to chemical or electrochemical reactions, and to study electrical and thermal conduction mechanisms in different organic electronic devices. FTIR microscopy was used to approach a realistic conduction mechanism by time-resolved chemical imaging of active materials in planar light-emitting electrochemical cells (LECs), investigated as an alternative to organic light emitting diodes (OLEDs). These chemical images are used for in-situ mapping of anion density profiles, polymer doping, and dynamic junction formation in the active layer under an applied bias. Results confirm the electrochemical doping model and help the systematic improvement of function and manufacture of LECs. Mixed ion-electron polymeric conductor materials such as PEDOT-PSS are used as active materials in organic thermoelectric generators (OTEGs), where charge carrier transport through the active layer promotes internal electrochemical reactions under a temperature gradient. FTIR microscopy and FTIR-attenuated total reflection (FTIR-ATR) were used to study thermoelectric and electrical properties of the conducting polymers. Recently, electrochemical supercapacitors have emerged as an alternative to conventional batteries, and polymeric materials are used to design polymer electrodes for renewable energy storage. To understand the charge transfer and structural changes of the polymer during the redox reaction, we have used FTIR-ATR as a tool for the in-situ spectroelectrochemical study of redox states in polypyrrole/lignin composites; we clarified the structural changes in the materials during charging and discharging of the composite. In further work, FTIR-ATR was also used for in-situ spectroelectrochemical studies of PEDOT:Cl, to monitor the effects of dissolved oxygen on PEDOT:Cl films, which are used as electrodes in renewable energy technologies. Further, time-resolved oxygen reduction reactions of PEDOT:Cl have been studied via polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS) to reveal chemical changes in electrochemically doped PEDOT upon exposure to oxygen.

Taken together, these studies provide an advancement in the use of infrared spectroscopy as a tool to understand electroactive materials under wet conditions, and have provided detailed chemical and electrochemical information of materials and devices under operation, that is not easily accessible with other methods.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. p. 61
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1884
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-142216 (URN)9789176854440 (ISBN)
Public defence
2017-11-17, Planck, F-House, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2017-10-23 Created: 2017-10-23 Last updated: 2017-10-23Bibliographically approved

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Ullah Khan, ZiaBubnova, OlgaJafari, Mohammad JavadLiu, XianjieGabrielsson, RogerEderth, ThomasFahlman, MatsCrispin, Xavier

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