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Studies of Materials and Interfaces for Organic Electronics
Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Organic electronics is a rapidly evolving field with vast number of applications having high potential for commercial success. Although a great progress has been made, many organic electronic applications: organic light-emitting diodes (OLEDs), organic fieldeffect transistors (OFETs), organic solar cells, etc; still require further optimization to fulfill the requirements for successful commercialization. For many applications, available at this time organic materials do not provide satisfactory performance and stability, which hinders the possibility of a large-scale production. Therefore, the key ingredient needed for a successful improvement in performance and stability of organic electronic devices is in-depth knowledge of physical and chemical properties of molecular and polymeric materials. Since many applications encompass several thin film layers made of organics, and often also inorganic materials, the understanding of both organic-organic and hybrid interfaces is yet another important issue necessary for the successful development of organic electronics.

The research presented in this thesis is based mainly on photoelectron spectroscopy, which is an experimental technique especially suited to study both surfaces and interfaces of materials. In the thesis, the properties of one of the most successful polymeric materials, poly(3,4-ethylenedioxythiophene), often abbreviated as PEDOT, have been extensively studied. The research was done in close cooperation with an industrial partner – AGFA Gevaert, Belgium. The study was focused on the exploration of the intrinsic properties of the material, such as stability, morphology and conductivity. In addition, however, a possibility of alternation of these properties was also explored. This thesis reports also about investigations of the properties of various organic-organic and hybrid interfaces. The energy level alignment at such interfaces plays important role in charge injection and performance of the thin film organic-based devices. The conditions for different energy level alignment regimes at the various interfaces have been studied. The studies on interfaces were performed in close collaboration with the R&D division of DuPont Corporation, USA. This work led to the significant advances in understanding of the interface energetics and properties of industryrelevant organic materials, as represented not only by published scientific papers, but also patent applications.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2007.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1103
Keyword [en]
Organic electronic, Polymeric materials, Organic light-emitting diodes (OLEDs), Organic fieldeffect transistors (OFETs), Organic solar cells
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:liu:diva-9488ISBN: 978-91-85831-94-4 (print)OAI: oai:DiVA.org:liu-9488DiVA: diva2:23946
Public defence
2007-06-08, Plank, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2007-07-03 Created: 2007-07-03 Last updated: 2009-04-23
List of papers
1. Light Induced Damage in Poly(3,4-ethylenedioxythiophene) and its Derivatives Studied by Photoelectron Spectroscopy
Open this publication in new window or tab >>Light Induced Damage in Poly(3,4-ethylenedioxythiophene) and its Derivatives Studied by Photoelectron Spectroscopy
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2004 (English)In: Synthetic metals, ISSN 0379-6779, Vol. 141, no 1-2, 67-73 p.Article in journal (Refereed) Published
Abstract [en]

Poly(3,4-ethylenedioxythiophene), usually known as PEDOT, and derivatives have attracted significant interest because of their high electrical conductivity. This electric property, however, deteriorates upon exposure to solar radiation. X-ray photoelectron spectroscopy (XPS) has been used to study the UV-light-induced chemical changes in doped PEDOT, as well as in both neutral and doped forms of its alkylated derivative—PEDOT-C14H29. Analysis of the XPS data indicates an oxidation of the sulfur in the thiophene ring. Apparently, photo-oxidation leads to the formation of sulfon groups, SO2, resulting in a disruption of π-conjugation in PEDOT, which there by diminishes the conductivity of the organic layer. This hypothesis is supported by the results of a study of model molecules for pristine and the oxidized PEDOT unit: 3,4 ethylenedioxythiophene (EDOT) and 3,4 ethylenedioxythiophene and S-dioxide (EDOT-SO2), respectively.

Place, publisher, year, edition, pages
Elsevier, 2004
Keyword
Poly(3, 4-ethylenedioxythiophene), X-ray photoelectron spectroscopy, Degradation, Photo-oxidation, Sulfon
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-14580 (URN)10.1016/j.synthmet.2003.08.017 (DOI)000220273400012 ()
Available from: 2007-07-03 Created: 2007-07-03 Last updated: 2015-03-20Bibliographically approved
2. Conductivity, Morphology, Interfacial Chemistry, and Stability of Poly(3,4- ethylene dioxythiophene)–Poly(styrene sulfonate): A Photoelectron Spectroscopy Study
Open this publication in new window or tab >>Conductivity, Morphology, Interfacial Chemistry, and Stability of Poly(3,4- ethylene dioxythiophene)–Poly(styrene sulfonate): A Photoelectron Spectroscopy Study
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2003 (English)In: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 41, no 21, 2561-2583 p.Article, review/survey (Refereed) Published
Abstract [en]

X-ray photoelectron spectroscopy (XPS) has been used to characterize poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDT/PSS), one of the most common electrically conducting organic polymers. A correlation has been established between the composition, morphology, and polymerization mechanism, on the one hand, and the electric conductivity of PEDT/PSS, on the other hand. XPS has been used to identify interfacial reactions occurring at the polymer-on-ITO and polymer-on-glass interfaces, as well as chemical changes within the polymer blend induced by electrical stress and exposure to ultraviolet light.

Place, publisher, year, edition, pages
John Wiley & Sons, 2003
Keyword
ESCA/XPS, poly(3, 4-ethylene dioxythiophene), conductivity, degradation, interfacial chemistry, conducting polymers
National Category
Polymer Chemistry Polymer Technologies
Identifiers
urn:nbn:se:liu:diva-14581 (URN)10.1002/polb.10659 (DOI)000185967300009 ()
Available from: 2007-07-03 Created: 2007-07-03 Last updated: 2016-11-24Bibliographically approved
3. Energy level alignment regimes at hybrid organic–organic and inorganic–organic interfaces
Open this publication in new window or tab >>Energy level alignment regimes at hybrid organic–organic and inorganic–organic interfaces
2007 (English)In: Organic Electronics, ISSN 1566-1199, Vol. 8, no 1, 14-20 p.Article in journal (Refereed) Published
Abstract [en]

Ultraviolet photoelectron spectroscopy has been used to determine the energy level alignment at interfaces of molecular hole-transporting materials and various conductive substrates. Depending on the work function of the substrate, s, a transition between two different energy level alignment regimes has been observed: namely vacuum level alignment and Fermi level pinning. The transition is associated with spontaneous positive charge transfer across the interface to the organic semiconductors above a certain material-specific threshold value of s. The charge transfer results in formation of an interfacial dipole of a magnitude that scales with s. In the vacuum level alignment regime, the hole-injection barriers scale linearly with s, while in the Fermi level pinning regime, these barriers are constant and independent of s.

Keyword
Energy level alignment; OLED; Hole-transporting materials; Interfaces; Photoelectron spectroscopy; Hole-injection barrier
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14582 (URN)10.1016/j.orgel.2006.10.006 (DOI)
Note
Original Publication: Slawomir Braun, Wojciech Osikowicz, Ying Wang and William R. Salaneck, Energy level alignment regimes at hybrid organic–organic and inorganic–organic interfaces, 2007, Organic Electronics, (8), 1, 14-20. http://dx.doi.org/10.1016/j.orgel.2006.10.006 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2007-07-03 Created: 2007-07-03 Last updated: 2010-05-19
4. Fermi level pinning at interfaces with tetrafluorotetracyanoquinodimethane (F4-TCNQ): The role of integer charge transfer states
Open this publication in new window or tab >>Fermi level pinning at interfaces with tetrafluorotetracyanoquinodimethane (F4-TCNQ): The role of integer charge transfer states
2007 (English)In: Chemical Physics Letters, ISSN 0009-2614, Vol. 438, no 4-6, 259-262 p.Article in journal (Refereed) Published
Abstract [en]

The energy level alignment of vacuum deposited molecular films of tetrafluorotetracyanoquinodimethane (F4-TCNQ) on various substrates has been studied by photoelectron spectroscopy. The interfaces studied span the work function range from 3.45 to 5.8 eV. In this range, the Fermi level of the substrate is pinned in proximity to LUMO level. This indicates that a charge transfer mechanism is responsible for the observed alignment scheme. The photoelectron emission study of sub-monolayer of F4-TCNQ revealed presence of electrons in the charge transfer states at the interface. In this context the electronic structure of neutral and negatively charged F4-TCNQ has been studied theoretically and by photoelectron spectroscopy.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14583 (URN)10.1016/j.cplett.2007.03.005 (DOI)
Available from: 2007-07-03 Created: 2007-07-03 Last updated: 2009-04-23
5. Energy level alignment of organic interfaces under reversal of deposition sequence: the role of Fermi level pinning
Open this publication in new window or tab >>Energy level alignment of organic interfaces under reversal of deposition sequence: the role of Fermi level pinning
2007 (English)Article in journal (Refereed) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14584 (URN)
Available from: 2007-07-03 Created: 2007-07-03

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