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Thermoelectric properties of conducting polymers
Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

According to different sources, from forty to sixty percent of the overall energy generated in the world today is squandered in waste heat. The existing energy conversion technologies are either close to their efficiency limits or too costly to justify their implementation. Therefore, the development of new technological approaches for waste heat recovery is highly demanded. The field of thermoelectrics can potentially provide an inexpensive, clean and efficient solution to waste heat underutilization, given that a new type of thermoelectric materials capable of meeting those requirements are available.

This thesis reports on strategies to optimize a thermoelectric efficiency (ZT) of conducting polymers, more specifically poly(3,4-ethylenedioxythiophene) (Pedot). Conducting polymers constitute a special class of semiconductors characterized by low thermal conductivity as well as electrical conductivity and thermopower that can be readily modified by doping in order to achieve the best combination of thermoelectric parameters. Conducting polymers that have never previously been regarded as hypothetically compatible for thermoelectric energy conversion, can exhibit promising thermoelectric performance at moderate temperatures, which is a sought-after quality for waste heat recovery. A rather substandard thermoelectric efficiency of Pedot-Pss can be markedly improved by various secondary dopants whose addition usually improves polymer’s morphology accompanied by a drastic increase in electrical conductivity and, consequently, in ZT. In order to enable further enhancement in thermoelectric properties, the optimization of the charge carrier concentration is commonly used. The oxidation level of Pedot-Pss can be precisely controlled by electrochemical doping resulting in a tenfold increase of ZT. In contrast to Pedot-Pss, another conducting polymer Pedot-Tos exhibits superior thermoelectric performance even without secondary doping owning to its partially crystalline nature that allows for an improved electronic conduction. With the aid of a strong electron donor, positively doped Pedot-Tos gets partially reduced reaching the optimum oxidation state at which its thermoelectric efficiency is just four times smaller than that of Be2Te3 and the highest among all stable conducting polymers. The downsides associated with chemical doping of Pedot-Tos such as doping inhomogeneity or chemical dopants air sensitivity can be surmounted if the doping level of Pedot-Tos is controlled by acidity/basicity of the polymer. This approach yields similar maximum thermoelectric efficiency but does not necessitate inert conditions for sample preparation. Optimized Pedot-Tos/Pedot-Pss can be functionalized as a p-type material in organic thermogenerators (OTEG) to power low energy electronic devices. If printed on large areas, OTEGs could be used as an alternative technique for capturing heat discarded by industrial processes, households, transportation sector or any natural heat sources for electricity production.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 53 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1491
Keyword [en]
Thermoelectric generation, Seebeck coefficient, conducting polymers, thermoelectric efficiency.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-87476ISBN: 978-91-7519-741-8 (print)OAI: oai:DiVA.org:liu-87476DiVA: diva2:589487
Public defence
2013-01-25, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-01-18 Created: 2013-01-18 Last updated: 2017-02-03Bibliographically approved
List of papers
1. Towards polymer-based organic thermoelectric generators
Open this publication in new window or tab >>Towards polymer-based organic thermoelectric generators
2012 (English)In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 5, no 11, 9345-9362 p.Article in journal (Refereed) Published
Abstract [en]

In response to the thread of environmental and ecological degradation along with projected fossil fuel depletion the active search for efficient renewable energy conversion technologies has been attempted in various research areas including the field of thermoelectrics. Despite the availability of considerable amounts of waste and natural heat stored in warm fluids (andlt;250 degrees C) a lack of environmentally friendly materials with high natural abundance, low manufacturing cost and high thermoelectric efficiency impedes the widespread use of thermoelectric generators for energy harvesting on a large scale. In this perspective, we examine the possibility of using organic conducting polymers in thermoelectric applications. We provide an overview of the background and the key concepts of organic thermoelectrics and illustrate some of the first prototypes of polymer-based organic thermoelectric generators.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85293 (URN)10.1039/c2ee22777k (DOI)000310006200015 ()
Note

Funding Agencies|European Research Council||Swedish foundation for strategic research||Knut and Alice Wallenberg foundation||Swedish Energy Agency||Advanced Functional Materials Center at Linkoping University||

Available from: 2012-11-19 Created: 2012-11-15 Last updated: 2017-12-07
2. Tuning the Thermoelectric Properties of Conducting Polymers in an Electrochemical Transistor
Open this publication in new window or tab >>Tuning the Thermoelectric Properties of Conducting Polymers in an Electrochemical Transistor
2012 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 40, 16456-16459 p.Article in journal (Refereed) Published
Abstract [en]

While organic field-effect transistors allow the investigation of interfacial charge transport at the semiconductor-dielectric interface, an electrochemical transistor truly modifies the oxidation level and conductivity throughout the bulk of an organic semiconductor. In this work, the thermoelectric properties of the bulk of the conducting polymer poly(3,4-ethylenedioxythiophene) -poly(styrene sulfonate) were controlled electrically by varying the gate voltage. In light of the growing interest in conducting polymers as thermoelectric generators, this method provides an easy tool to study the physics behind the thermoelectric properties and to optimize polymer thermoelectrics.

Place, publisher, year, edition, pages
American Chemical Society, 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85195 (URN)10.1021/ja305188r (DOI)000309566400003 ()
Note

Funding Agencies|Swedish Foundation for Strategic Research||Knut and Alice Wallenberg Foundation||Swedish Energy Agency||Advanced Functional Materials Center at Linkoping University||ERC Starting Grant||

Available from: 2012-11-09 Created: 2012-11-09 Last updated: 2017-12-07
3. Optimization of the thermoelectric figure of merit in the conducting polymer poly(3,4-ethylenedioxythiophene)
Open this publication in new window or tab >>Optimization of the thermoelectric figure of merit in the conducting polymer poly(3,4-ethylenedioxythiophene)
Show others...
2011 (English)In: NATURE MATERIALS, ISSN 1476-1122, Vol. 10, no 6, 429-433 p.Article in journal (Refereed) Published
Abstract [en]

Thermoelectric generators (TEGs) transform a heat flow into electricity. Thermoelectric materials are being investigated for electricity production from waste heat (co-generation) and natural heat sources. For temperatures below 200 degrees C, the best commercially available inorganic semiconductors are bismuth telluride (Bi2Te3)-based alloys, which possess a figure of merit ZT close to one(1). Most of the recently discovered thermoelectric materials with ZT andgt; 2 exhibit one common property, namely their low lattice thermal conductivities(2,3). Nevertheless, a high ZT value is not enough to create a viable technology platform for energy harvesting. To generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs. This requires thermoelectric materials that are readily synthesized, air stable, environmentally friendly and solution processable to create patterns on large areas. Here we show that conducting polymers might be capable of meeting these demands. The accurate control of the oxidation level in poly(3,4-ethylenedioxythiophene) (PEDOT) combined with its low intrinsic thermal conductivity (lambda = D 0.37W m(-1) K-1) yields a ZT = 0.25 at room temperature that approaches the values required for efficient devices.

Place, publisher, year, edition, pages
Nature Publishing Group, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-68783 (URN)10.1038/nmat3012 (DOI)000290855100016 ()
Available from: 2011-06-08 Created: 2011-06-07 Last updated: 2017-02-03

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