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Semi-metallic polymers
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
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2014 (English)In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 13, no 2, 190-194 p.Article in journal (Refereed) Published
Abstract [en]

Polymers are lightweight, flexible, solution-processable materials that are promising for low-cost printed electronics as well as for mass-produced and large-area applications. Previous studies demonstrated that they can possess insulating, semiconducting or metallic properties; here we report that polymers can also be semi-metallic. Semi-metals, exemplified by bismuth, graphite and telluride alloys, have no energy bandgap and a very low density of states at the Fermi level. Furthermore, they typically have a higher Seebeck coefficient and lower thermal conductivities compared with metals, thus being suitable for thermoelectric applications. We measure the thermoelectric properties of various poly( 3,4-ethylenedioxythiophene) samples, and observe a marked increase in the Seebeck coefficient when the electrical conductivity is enhanced through molecular organization. This initiates the transition from a Fermi glass to a semi-metal. The high Seebeck value, the metallic conductivity at room temperature and the absence of unpaired electron spins makes polymer semi-metals attractive for thermoelectrics and spintronics.

Place, publisher, year, edition, pages
Nature Publishing Group , 2014. Vol. 13, no 2, 190-194 p.
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-104644DOI: 10.1038/nmat3824ISI: 000330182700027OAI: diva2:698183
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2015-10-14
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. 50 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1709
Thermoelectricity, conducting polymers, thermoelectric devices
National Category
Physical Sciences Electrical Engineering, Electronic Engineering, Information Engineering
urn:nbn:se:liu:diva-121982 (URN)978-91-7685-931-5 (print) (ISBN)
Public defence
2015-11-12, Resuren (Pronova), Campus Norrköping, Norrköping, 10:00 (English)
Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-10-14Bibliographically approved

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