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Materials study of organic electronics
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The electronic structure of materials for use in organic electronics is studied in this thesis. The first part includes applied research in the form of studies of polymers for use in polymer light emitting devices. The second part is more directed toward organic based spintronics and contains research regarding a room temperature organic ferrimagnetic material. Common for the studies, apart from that all regard organic material, are the use of electron spectroscopy techniques. The studies give new spectroscopic evidence of how the energy level alignment occurs between electrical conductors and spin coated semiconducting polymers, i.e. alignment at the anode side of polymer light emitting devices. The studies prove theoretical predictions regarding spontaneous charge injection forming positive polaronic species in the semiconducting polymer, pinned to the Fermi level of the substrate. The first part also includes studies of novel conducting polymers, based on PEDOT and polyaniline, with work functions spanning from 4.2 eV to 6.4 eV. In the case of organic magnets, our design and construction of the purpose built vacuum deposition system allowed for the first time oxygen free films of the extremely reactive organic ferrimagnet, vanadium tetracyanoethylene (V(TCNE)x), to be studied by means of several different electron spectroscopies, proving or disproving several previous results and assumptions.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2005. , 48 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 971
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-32276Local ID: 18164ISBN: 91-85457-30-2 (print)OAI: oai:DiVA.org:liu-32276DiVA: diva2:253098
Public defence
2005-10-21, Hörsal K3, Campus Norrköping, Norrköping, 10:15 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-11-23
List of papers
1. Study and comparison of conducting polymer hole injection layers in light emitting devices
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2005 (English)In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 6, no 1, 21-33 p.Article in journal (Refereed) Published
Abstract [en]

A set of polyaniline- and poly(3,4-ethylene dioxythiophene)-based materials were studied as hole injection layers in polymer light emitting devices. The choice of polymeric counterion/dopant poly(styrenesulfonic acid), and poly(acrylamido-2-methyl-1-propanesulfonic acid), and poly(acrylamide) blended with polyaniline/poly(acrylamido-2-methyl-1-propanesulfonic acid) was found to influence both work function and film morphology, which in turn affects device performance. The work functions of the polymer films spanned the range of over 1 eV and the surface region of the films were found to be low in conducting polymer content compared to the bulk. This was particularly the case of the polyaniline/poly(acrylamido-2-methyl-1-propanesulfonic acid) blended with poly(acrylamide) which showed device efficiency equal to that of the poly(3,4-ethylene dioxythiophene)–poly(styrenesulfonic acid) reference. The turn on voltage, however, was significantly larger, likely due to the insulating poly(acrylamide)-rich surface region of the polyaniline/poly(acrylamido-2-methyl-1-propanesulfonic acid)/poly(acrylamide) film. The polymer blend of polyaniline/poly(styrenesulfonic acid) yielded the highest work function (5.5 ± 0.1 eV).

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-32255 (URN)10.1016/j.orgel.2005.02.001 (DOI)18135 (Local ID)18135 (Archive number)18135 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
2. Poly(3.4-ethylene dioxythiophene)- and polyaniliane-Poly(perfluoroethylenesulfonic acid) as hole injecting layers in polymer light emitting devices
Open this publication in new window or tab >>Poly(3.4-ethylene dioxythiophene)- and polyaniliane-Poly(perfluoroethylenesulfonic acid) as hole injecting layers in polymer light emitting devices
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We present a study of poly(3,4-ethylene dioxythiophene), PEDOT, and polyaniline, where poly(perfluoroethylenesulfonic acid), PFESA has been used as counter ion and dopant respectively. The study was done in order to establish how the material petfonns as hole injecting layers in polymer light emitting devices. A total of 19 different PEDOT-PFESA samples and three different PAni-PFESA systems were studied, each with a different acidity, ranging between pH 1.6 to pH 7.7. The highest work function obtained was 6.0 eV and work function and acidity correlate such that significantly higher work functions are obtained for higher acidities. Photoelectron spectroscopy and Atomic Force Microscopy data suggest that the resulting fihns have grain structured morphology where the PAni-PFESA and PEDOT-PFESA systems form inverse micelles, i.e. PEDOT or PAni together with counter ions as an inner core surrounded by mainly the PFESA backbone.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85555 (URN)
Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2013-10-31
3. UV-ozone treatment of PEDOT-based materials resulting in increased work functions
Open this publication in new window or tab >>UV-ozone treatment of PEDOT-based materials resulting in increased work functions
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We describe a simple method to increase the work function of PEDOT-PFESA and PEDOT-PSS by short exposure to UV and ozone in a "UVO-Cleaner®". The creation of carbonyl gmups in the surface region fotms a dipole layer shifting the vacuum level with a followed increase in work function. It has been shown that the work function of PEDOT-PFESA can be increased by as much as -0.4 eV to the absolute value of 6.3 eV and by at least -0.2 eV for PEDOT-PSS to the absolute value of 5.4 e V. The increase in work function has also proven to be time dependent with the largest increasing rate occuning for short exposure times. Upon ozone treatment, both PEDOT and PSS are oxidized whereas PFESA seems to be unaffected.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85556 (URN)
Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2012-11-23
4. Fermi-level pinning at conjugated polymer interfaces
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2006 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 5, 53502- p.Article in journal (Refereed) Published
Abstract [en]

Photoelectron spectroscopy has been used to map out energy level alignment of conjugated polymers at various organic-organic and hybrid interfaces. Specifically, we have investigated the hole-injection interface between the substrate and light-emitting polymer. Two different alignment regimes have been observed: (i) Vacuum-level alignment, which corresponds to the lack of vacuum-level offsets (Schottky–Mott limit) and (ii) Fermi-level pinning, where the substrate Fermi level and the positive polaronic level of the polymer align. The observation is rationalized in terms of spontaneous charge transfer whenever the substrate Fermi level exceeds the positive polaron/bipolaron formation energy per particle. The charge transfer leads to the formation of an interfacial dipole, as large as 2.1 eV.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-36176 (URN)10.1063/1.2168515 (DOI)30408 (Local ID)30408 (Archive number)30408 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
5. Coulomb interactions in rubidium-doped tetracyanoethylene: a model system for organometallic magnets
Open this publication in new window or tab >>Coulomb interactions in rubidium-doped tetracyanoethylene: a model system for organometallic magnets
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2004 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 16, 165208- p.Article in journal (Refereed) Published
Abstract [en]

The electronic structure of tetracyanoethylene (TCNE) has been studied both in its pristine state and upon stepwise rubidium intercalation, by UV and x-ray photoelectron spectroscopy as well as with theoretical calculations. The intercalated system may serve as a model for TCNE-based organometallic magnets, of which the electronic structure remains largely unknown. Rubidium is found to n-dope the TCNE molecules forming Rb+TCNE- with almost complete charge transfer. Calculations show a spin splitting of the former highest occupied molecular orbital level upon Rb doping. We see no evidence for the formation of doubly charged TCNE molecules. A gap opens up at the Fermi energy for Rb+TCNE- due to on-site Coulomb interactions. We estimate the on-site Coulomb interaction of amorphous TCNE doped with Rb to be ∼2 eV.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13871 (URN)10.1103/PhysRevB.69.165208 (DOI)
Available from: 2006-06-28 Created: 2006-06-28 Last updated: 2017-12-13
6. V(TCNE)x: the electronic structure of an enigmatic, organic-based room temperature magnet revealed
Open this publication in new window or tab >>V(TCNE)x: the electronic structure of an enigmatic, organic-based room temperature magnet revealed
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We have prepared and characterized thin films of V(TCNE)x in ultra-high vacuum using a novel film growth technique based on in-situ chemical vapor deposition of tetracyanoethylene, TCNE, and bis-benzene vanadium, V(C6H6)2. The in-situ preparation method enabled, for the first time, experimental analysis of the electronic structure. X-ray magnetic circular dichroism (XMCD) measurements recorded at the V L2,3-edge confirmed room temperature magnetic ordering. A combination of conventional photoelectron spectroscopy (PES) and resonant photoemission (RPE) measured at the x-ray absorption edges (V L3-edge, C K-edge, N K-edge) shows that the highest occupied electronic state is V(3d)-derived. Nearly complete quenching of the V(3d) orbital angular momentum is observed from the low value of the integrated XMCD signal, indicating a strong ligand field. The rearrangements of the TCNE" related valance electronic states observed in PED and near edge x-ray absorption fine structure (NEXAFS) spectra, in combination with the evidence of V(3d) and TCNE" π (π*) orbital overlap contained in RPE spectra, also point to strong, covalent type bonding.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-85558 (URN)
Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2012-11-23

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