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Thermoelectric Properties of Polymeric Mixed Conductors
Linköpings universitet, Institutionen för teknik och naturvetenskap, Fysik och elektroteknik. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0003-2930-676X
Linköpings universitet, Institutionen för fysik, kemi och biologi, Molekylär fysik. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0003-3899-4891
Linköpings universitet, Institutionen för teknik och naturvetenskap. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Molekylär fysik. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0002-1639-5735
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2016 (Engelska)Ingår i: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 26, nr 34, s. 6288-6296Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The thermoelectric (TE) phenomena are intensively explored by the scientific community due to the rather inefficient way energy resources are used with a large fraction of energy wasted in the form of heat. Among various materials, mixed ion-electron conductors (MIEC) are recently being explored as potential thermoelectrics, primarily due to their low thermal conductivity. The combination of electronic and ionic charge carriers in those inorganic or organic materials leads to complex evolution of the thermovoltage (Voc) with time, temperature, and/or humidity. One of the most promising organic thermoelectric materials, poly(3,4-ethyelenedioxythiophene)-polystyrene sulfonate (PEDOT-PSS), is an MIEC. A previous study reveals that at high humidity, PEDOT-PSS undergoes an ionic Seebeck effect due to mobile protons. Yet, this phenomenon is not well understood. In this work, the time dependence of the Voc is studied and its behavior from the contribution of both charge carriers (holes and protons) is explained. The presence of a complex reorganization of the charge carriers promoting an internal electrochemical reaction within the polymer film is identified. Interestingly, it is demonstrated that the time dependence behavior of Voc is a way to distinguish between three classes of polymeric materials: electronic conductor, ionic conductor, and mixed ionic–electronic conductor

Ort, förlag, år, upplaga, sidor
Wiley-VCH Verlagsgesellschaft, 2016. Vol. 26, nr 34, s. 6288-6296
Nationell ämneskategori
Oorganisk kemi
Identifikatorer
URN: urn:nbn:se:liu:diva-133171DOI: 10.1002/adfm.201601106ISI: 000383609300015Scopus ID: 2-s2.0-84978042566OAI: oai:DiVA.org:liu-133171DiVA, id: diva2:1055411
Forskningsfinansiär
EU, Europeiska forskningsrådet, 307596
Anmärkning

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

Tillgänglig från: 2016-12-12 Skapad: 2016-12-12 Senast uppdaterad: 2018-08-31Bibliografiskt granskad
Ingår i avhandling
1. Application of Vibrational Spectroscopy in Organic Electronics
Öppna denna publikation i ny flik eller fönster >>Application of Vibrational Spectroscopy in Organic Electronics
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2017. s. 61
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1884
Nationell ämneskategori
Atom- och molekylfysik och optik
Identifikatorer
urn:nbn:se:liu:diva-142216 (URN)9789176854440 (ISBN)
Disputation
2017-11-17, Planck, F-House, Campus Valla, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2017-10-23 Skapad: 2017-10-23 Senast uppdaterad: 2017-10-23Bibliografiskt granskad

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