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Control of phase separation in blends of polyfluorene (co)polymers and the C60-derivative PCBM
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. (Materialfysik)
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science. (Fysik)
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science. (Materialfysik)ORCID iD: 0000-0002-1609-8909
2005 (English)In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 152, no 1-3, p. 109-112Article in journal (Refereed) Published
Abstract [en]

When creating thin films of polymer blends, interesting morphologies are formed because of phaseseparation. In particular for conjugated polymers, which are used as active material in optoelectronic devices, it is very important to understand the parameters that influence the phaseseparation process and to achieve control over the morphology. The overall goal of this blend morphology study is to contribute to the design of device structures with desired performance.

Here we present results of morphology studies on thin films of polyfluorene-based blends with the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The polymers used are poly(9,9-dioctylfluorene) (F8) and four different copolymers of F8. The thin films are spin coated from chloroform solutions onto silicon substrates and their surface morphology is imaged by tapping mode atomic force microscopy (AFM). We observe that the size and the shape of the domains in the film depend on the structure of the polymer. The nature of the monomer that, together with F8, is building the repeating unit in the copolymers has a strong effect on the phaseseparation in the polymer: PCBMblend. Since phaseseparation is influenced by interactions between components of the blend and the solvent, these results indicate that the degree of chemical interaction between polymer, solvent and PCBM, is different for the different blends. For the systems that form larger domains there is a clear correlation between the domain size (area) and the polymer/PCBMblend ratio. We also observe that the spin speed affects the thickness of the films and that the domain size increases with increasing thickness, primarily due to longer drying times

Place, publisher, year, edition, pages
Elsevier , 2005. Vol. 152, no 1-3, p. 109-112
Keywords [en]
Atomic force microscopy; Spin coating; Morphology; Conjugated polymers; Blend
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kau:diva-1934DOI: 10.1016/j.synthmet.2005.07.195OAI: oai:DiVA.org:kau-1934DiVA, id: diva2:5080
Conference
Proceedings of the International Conference on Science and Technology of Synthetic Metals: Wollongong, Australia, June 28 - July 2, 2004
Available from: 2007-11-20 Created: 2007-11-20 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Thin films of polyfluorene:fullerene blends - Morphology and its role in solar cell performance
Open this publication in new window or tab >>Thin films of polyfluorene:fullerene blends - Morphology and its role in solar cell performance
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The sun provides us daily with large quantities of energy in the form of light. With the world’s increasing demand of electrical energy the prospect of converting this solar light into electricity is highly tempting. In the strive towards mass-production and low cost solar cells, new types of solar cells are being developed, e.g. solar cells completely based on organic molecules and polymers. These materials offer a promising potential of low cost and large scale manufacturing and have the additional advantage that they can be produced on flexible and light weight substrate which opens for new and innovating application areas, e.g. integration with paper or textiles, or as building materials. In polymer solar cells a combination of two materials are used, an electron donor and an electron acceptor. The three dimensional distribution of the donor and acceptor in the active layer of the device, i.e. the morphology, is known to have larger influence of the solar cell performance. For the optimal morphology there is a trade-off between sometimes conflicting criteria for the various steps of the energy conversion process. The dissociation of photogenerated excitons takes place at an interface between the donor and acceptor materials. Therefore an efficient generation of charges requires a large interface between the two components. However, for charge transport and collection at the electrodes, continuous pathways for the charges to the electrodes are required.

In this thesis, results from morphology studies by atomic force microscopy (AFM) and dynamic secondary ion mass spectrometry (SIMS) of spin-coated blend and bilayer thin films of polyfluorene co-polymers, especially poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4´,7´-di-2-thienyl-2´,1´,3´-benzothiadiazole)] APFO-3, and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are presented. It is shown that by varying the blend ratio, the spin.-coating solvent, and/or the substrate, different morphologies can be obtained, e.g. diffuse bilayer structures, spontaneously formed multilayer structures and homogeneous blends. The connection between these different morphologies and the performance of solar cells is also analysed. The results indicate that nano-scale engineering of the morphology in the active layer may be an important factor in the optimization of the performance of polymer solar cells.

Place, publisher, year, edition, pages
Fakulteten för teknik- och naturvetenskap, 2007
Series
Karlstad University Studies, ISSN 1403-8099 ; 2007:43
Keywords
Polymer Solar Cells, Polymer Blends, Morphology, Polyfluorene, PCBM, AFM, SIMS, Spin-Coating, Surface Directed Spinodal Decomposition
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-1243 (URN)978-91-7063-147-4 (ISBN)
Public defence
2007-12-07, 1B 364 (Frödingsalen), Karlstads universitet, Karlstad, 13:15
Opponent
Supervisors
Available from: 2007-11-20 Created: 2007-11-20
2. Morphology studies of thin films of polyfluorene: fullerene blends
Open this publication in new window or tab >>Morphology studies of thin films of polyfluorene: fullerene blends
2005 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The formation of thin films of polymer blends by spin-coating from solution is characterised by rapid solvent quenching, a process that results in non-equilibrium morphologies. Thin films of conjugated polymer blends are used as the active material in polymer solar cells, in which the morphology may have drastic effects on device performance.

In this thesis results from morphology studies are presented for spin-coated thin films of polyfluorenes and co-polymers of polyfluorene blended with the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The surface morphology was investigated by atomic force microscopy (AFM) and was found to depend on the blend ratio as well as the chemical structure of the blend components. The spin speed, which determines the thickness of the spin-coated thin films, was also found to influence the morphology. Secondary ion mass spectrometry (SIMS) was used for depth profiling of the chemical composition in thin films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4´,7´-di-2-thienyl-2´,1´,3´-benzothiadiazole)] (LBPF5) blended with PCBM. The films were found to be vertically phase separated with a four-fold multilayered structure.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2005
Series
Karlstad University Studies, ISSN 1403-8099 ; 2005:26
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-2361 (URN)91-85335-67-3 (ISBN)
Presentation
2005-09-02, Nyqvistsalen, 9C 203, Karlstads universitetKarlstad, 13:30 (English)
Opponent
Supervisors
Available from: 2009-06-09 Created: 2009-06-09 Last updated: 2012-11-28Bibliographically approved

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Magnusson, KjellMoons, Ellen

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