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Morphology studies of thin films of polyfluorene: fullerene blends
Karlstad University, Division for Engineering Sciences, Physics and Mathematics.
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: urn:nbn:se:kau:diva-2361ISBN: 91-85335-67-3 (print)OAI: oai:DiVA.org:kau-2361DiVA, id: diva2:24703
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
List of papers
1. Multilayer formation in spin-coated thin films of low-bandgap polyfluorene:PCBM blends
Open this publication in new window or tab >>Multilayer formation in spin-coated thin films of low-bandgap polyfluorene:PCBM blends
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2005 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, no 50, p. L529-L534Article in journal (Refereed) Published
Abstract [en]

Blends of the low-bandgap polymer 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) were spin-coated from chloroform solution into thin films, which were examined with dynamic secondary ion mass spectrometry. For blends with high PCBM content, the depth profiles show composition waves that were caused by surface-directed phase separation during spin-coating. The formation of such multilayer structures by spontaneous self-stratification is likely to have implications for optimization strategies for the performance of organic solar cells

Place, publisher, year, edition, pages
Philadelphia: Institute of Physics Publishing (IOPP), 2005
Keywords
Soft matter, liquids and polymers, Condensed matter: electrical, magnetic and optical, Surfaces, interfaces and thin films, Nanoscale science and low-D systems
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-1935 (URN)10.1088/0953-8984/17/50/L01 (DOI)
Available from: 2007-11-20 Created: 2007-11-20 Last updated: 2017-12-07Bibliographically approved
2. Control of phase separation in blends of polyfluorene (co)polymers and the C60-derivative PCBM
Open this publication in new window or tab >>Control of phase separation in blends of polyfluorene (co)polymers and the C60-derivative PCBM
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
Keywords
Atomic force microscopy; Spin coating; Morphology; Conjugated polymers; Blend
National Category
Physical Sciences
Identifiers
urn:nbn:se:kau:diva-1934 (URN)10.1016/j.synthmet.2005.07.195 (DOI)
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

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