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Osikowicz, Wojciech
Publications (10 of 35) Show all publications
Fahlman, M., Sehati, P., Osikowicz, W., Braun, S., de Jong, M. P. & Brocks, G. (2013). Photoelectron spectroscopy and modeling of interface properties related to organic photovoltaic cells. Journal of Electron Spectroscopy and Related Phenomena, 190, 33-41
Open this publication in new window or tab >>Photoelectron spectroscopy and modeling of interface properties related to organic photovoltaic cells
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2013 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 190, p. 33-41Article in journal (Refereed) Published
Abstract [en]

In this short review, we will give examples on how photoelectron spectroscopy (PES) assisted by models on interface energetics can be used to study properties important to bulk heterojunction type organic photovoltaic devices focusing on the well-known bulk heterojunction blend of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) and its model system P3HT:C-60. We also will discuss some of the limitations of PES as applied to organic semiconductors (OS) and photovoltaic devices and finish with reviewing recent theoretical advances that now enable calculation of relevant parameters at (hybrid) interfaces measured by PES.

Place, publisher, year, edition, pages
Elsevier, 2013
Keywords
Photoelectron spectroscopy; Photovoltaics; Organic semiconductors; Interfaces
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-103884 (URN)10.1016/j.elspec.2013.02.001 (DOI)000329376800005 ()
Available from: 2014-01-30 Created: 2014-01-30 Last updated: 2017-12-06
de Jong, M. P., Osikowicz, W., Sorensen, S., Sergeyev, S., Geerts, Y. & Salaneck, W. R. (2008). Femtosecond charge transfer in assemblies of discotic liquid crystals. The Journal of Physical Chemistry C, 112(40), 15784-15790
Open this publication in new window or tab >>Femtosecond charge transfer in assemblies of discotic liquid crystals
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2008 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 40, p. 15784-15790Article in journal (Refereed) Published
Abstract [en]

The electronic coupling strength within columns of discotic liquid crystals is investigated using core-level resonant photoemission spectroscopy. Coexisting well-ordered and disordered regions are identified in thin films of tetra-alkoxy-substituted phthalocyanines with the aid of near edge X-ray absorption fine structure and photoelectron spectroscopies. These different regions are used to derive a lower limit for the intermolecular charge transfer bandwidth within the framework of the core-hole clock principle. We find average charge transfer times on the order of a few femtoseconds, that is, significantly faster than the C(ls) core-hole lifetime, which indicates a surprisingly strong electronic coupling between the phthalocyanine units as compared to what is expected from the charge transport characteristics of this material. © 2008 American Chemical Society.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49943 (URN)10.1021/jp8037494 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Tsao, H., Pisula, W., Liu, Z., Osikowicz, W., Salaneck, W. R. & Mullen, K. (2008). From ambi- To unipolar behavior in discotic dye field-effect transistors. Advanced Materials, 20(14), 2715-2719
Open this publication in new window or tab >>From ambi- To unipolar behavior in discotic dye field-effect transistors
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2008 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 20, no 14, p. 2715-2719Article in journal (Refereed) Published
Abstract [en]

A study was conducted to demonstrate solution-processable ambipolar organic field-effect transistors based on a discotic dye. Such single component devices allow the study of the influence of supramolecular ordering on FET charge transport properties. These transistors exhibited ambipolarity even without any structural order. The absence of p-type behavior could not be explained by the increase of hole injection barrier or by interface trapping. It was rather observed that the change in morphology most probably lead to such a phenomenon. These findings further suggest that besides charge injection barriers and interface trapping, structural composition, that is, microscopic domain boundaries together with local defects in one-dimensional columnar systems, also trigger the loss of ambipolarity owing to lowering of the minority charge carrier mobility.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47099 (URN)10.1002/adma.200702992 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Lindell, L., Unge, M., Osikowicz, W., Stafström, S., Salaneck, W. R., Crispin, X. & de Jong, M. P. (2008). Integer charge transfer at the tetrakis(dimethylamino)ethylene/Au interface. Applied Physics Letters, 92(16), 163302-1-163302-3
Open this publication in new window or tab >>Integer charge transfer at the tetrakis(dimethylamino)ethylene/Au interface
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2008 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 16, p. 163302-1-163302-3Article in journal (Refereed) Published
Abstract [en]

In organic-based electronics, interfacial properties have a profound impact on device performance. The lineup of energy levels is usually dependent on interface dipoles, which may arise from charge transfer reactions. In many applications, metal-organic junctions are prepared under ambient conditions, where direct overlap of the organic system from the metal bands is prevented due to presence of oxides and/or hydrocarbons. We present direct experimental and theoretical evidence showing that the interface energetic for such systems is governed by exchange of an integer amount of electrons.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-20776 (URN)10.1063/1.2912818 (DOI)
Available from: 2009-09-18 Created: 2009-09-18 Last updated: 2017-12-13
Andersson, M., Osikowicz, W., Jakobsson, F. L. .., Berggren, M., Lindgren, L., Andersson, M. & Inganäs, O. (2008). Intrinsic and extrinsic influences on the temperature dependence of mobility in conjugated polymers. Organic electronics, 9(5), 569-574
Open this publication in new window or tab >>Intrinsic and extrinsic influences on the temperature dependence of mobility in conjugated polymers
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2008 (English)In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 9, no 5, p. 569-574Article in journal (Refereed) Published
Abstract [en]

The temperature dependence of charge carrier mobility in conjugated polymers and their blends with fullerenes is investigated with different electrical methods, through field effect transistor (FET), space charge limited current (SCLC) and charge extraction (CELIV) measurements. Simple models, such as the Gaussian disorder model (GDM), are shown to accurately predict the temperature behavior, and a good correlation between the different measurement methods is obtained. Inconsistent charge carrier concentrations in the modeling are explained through intrinsic non-equilibrium effects, and are responsible for the limited applicability of existing numerical models. A severe extrinsic influence from water in FETs with a hydrophilic insulator interface is also demonstrated. The presence of water leads to a significant overestimate of the disorder in the materials from measurements close to room temperature and erratic behavior in the 150-350 K range. To circumvent this problem it is shown to be necessary to measure under ultra high vacuum (UHV) conditions. © 2008 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2008
Keywords
Electrical transport, Field effect transistor, Fullerene, Mobility, Polymer, Temperature dependence
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-50043 (URN)10.1016/j.orgel.2008.03.002 (DOI)
Note

The previous status of this article was Manuscript.

Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12Bibliographically approved
Fahlman, M., Crispin, A., Crispin, X., Henze, S., de Jong, M. P., Osikowicz, W., . . . Salaneck, W. R. (2007). Electronic structure of hybrid interfaces for polymer-based electronics. Journal of Physics: Condensed Matter, 19(18)
Open this publication in new window or tab >>Electronic structure of hybrid interfaces for polymer-based electronics
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2007 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 18Article, review/survey (Refereed) Published
Abstract [en]

The fundamentals of the energy level alignment at anode and cathode electrodes in organic electronics are described. We focus on two different models that treat weakly interacting organic/metal (and organic/organic) interfaces: the induced density of interfacial states model and the so-called integer charge transfer model. The two models are compared and evaluated, mainly using photoelectron spectroscopy data of the energy level alignment of conjugated polymers and molecules at various organic/metal and organic/organic interfaces. We show that two different alignment regimes are generally observed: (i) vacuum level alignment, which corresponds to the lack of vacuum level offsets (Schottky-Mott limit) and hence the lack of charge transfer across the interface, and (ii) Fermi level pinning where the resulting work function of an organic/metal and organic/organic bilayer is independent of the substrate work function and an interface dipole is formed due to charge transfer across the interface. We argue that the experimental results are best described by the integer charge transfer model which predicts the vacuum level alignment when the substrate work function is above the positive charge transfer level and below the negative charge transfer level of the conjugated material. The model further predicts Fermi level pinning to the positive (negative) charge transfer level when the substrate work function is below (above) the positive (negative) charge transfer level. The nature of the integer charge transfer levels depend on the materials system: for conjugated large molecules and polymers, the integer charge transfer states are polarons or bipolarons, for small molecules' highest occupied and lowest unoccupied molecular orbitals and for crystalline systems, the relevant levels are the valence and conduction band edges. Finally, limits and further improvements to the integer charge transfer model are discussed as well as the impact on device design. © IOP Publishing Ltd.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49754 (URN)10.1088/0953-8984/19/18/183202 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Braun, S., Osikowicz, W., Wang, Y. & Salaneck, W. R. (2007). Energy level alignment regimes at hybrid organic–organic and inorganic–organic interfaces. Organic Electronics, 8(1), 14-20
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, p. 14-20Article 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.

Keywords
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
Osikowicz, W., de Jong, M. P. & Salaneck, W. R. (2007). Formation of the interfacial dipole at organic-organic interfaces: C 60/polymer interfaces. Advanced Materials, 19(23), 4213-4217
Open this publication in new window or tab >>Formation of the interfacial dipole at organic-organic interfaces: C 60/polymer interfaces
2007 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 19, no 23, p. 4213-4217Article in journal (Refereed) Published
Abstract [en]

The energetics at organic-organic interfaces comprising a thin film of a p-conjugated polymer and an overlayer of fullerene C60 was investigated. Two different polymers, poly(3-hexylthiophene) or P3HT, a polymer with moderate electron donor character were investigated. P3HT films were spin-coated from 5 mg mL-1 and 20 mg mL solutions in dichlorobenzene on conductive substrates such as native oxide terminated silicon SiO x/Si and aluminum, cleaned in acetone and isopropyl alcohol prior to spin coating and UV ozone treated gold. The thickness of the resulting polymer films obtained from the solutions with high concentrations was about 20 nm and 150 nm, as determined from reflectance ellipsometry. The results suggested that integer charge transfer provides a comprehensive description of energy level alignment at interfaces of organic semiconductors.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47388 (URN)10.1002/adma.200700622 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Braun, S., de Jong, M., Osikowicz, W. & Salaneck, W. R. (2007). Influence of the electrode work function on the energy level alignment at organic-organic interfaces. Applied Physics Letters, 91(20)
Open this publication in new window or tab >>Influence of the electrode work function on the energy level alignment at organic-organic interfaces
2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 20Article in journal (Refereed) Published
Abstract [en]

The energy level alignment at interfaces, in stacks comprising of (4, 4′ -N, N′ -dicarbazolyl-biphenyl) (CBP), (4,4, 4″ -tris[3-methyl-phenyl(phenyl)amino]-triphenylamine) (m -MTDATA), and a conductive substrate, has been studied. We show that the alignment of energy levels depends on the equilibration of the chemical potential throughout the layer stack, while any electronic coupling between the individual layers is of lesser importance. This behavior is expected to occur for a broad class of weakly interacting interfaces and can have profound consequences for the design of organic electronic devices. © 2007 American Institute of Physics.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-39542 (URN)10.1063/1.2806938 (DOI)49585 (Local ID)49585 (Archive number)49585 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
De Cupere, V., Tant, J., Viville, P., Lazzaroni, R., Osikowicz, W., Salaneck, W. R. & Geerts, Y. H. (2006). Effect of interfaces on the alignment of a discotic liquid-crystalline phthalocyanine. Langmuir, 22(18), 7798-7806
Open this publication in new window or tab >>Effect of interfaces on the alignment of a discotic liquid-crystalline phthalocyanine
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2006 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 18, p. 7798-7806Article in journal (Refereed) Published
Abstract [en]

This paper deals with the influence of the nature and number of solid interfaces on the alignment of the columns in a semiconducting discotic liquid crystal. The solid substrates have been characterized in terms of their roughness and surface energy. The alignment of the discotic liquid crystal columns on these substrates has been determined by optical microscopy under crossed polarizers and by tapping-mode atomic force microscopy. The nature of the substrates has negligible influence on the alignment. The key parameter is the confinement imposed to the film. These surprising observations are explained by the antagonist alignment role of gas and solid interfaces. © 2006 American Chemical Society.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-36040 (URN)10.1021/la0605182 (DOI)29550 (Local ID)29550 (Archive number)29550 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
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