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Multilayer formation in spin-coated thin films of low-bandgap polyfluorene:PCBM blends
Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. (Materialfysik)
Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Kraków, Poland.
Institute of Physics, Jagiellonian University, Kraków, Poland.
Institute of Physics, Jagiellonian University, Kraków, Poland.
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2005 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, no 50, L529-L534 p.Article 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. Vol. 17, no 50, L529-L534 p.
Keyword [en]
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: urn:nbn:se:kau:diva-1935DOI: 10.1088/0953-8984/17/50/L01OAI: oai:DiVA.org:kau-1935DiVA: diva2:5081
Available from: 2007-11-20 Created: 2007-11-20 Last updated: 2016-08-11Bibliographically 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
Keyword
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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