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Carbon nanotubes and graphene polymer composites for opto-electronic applications
Umeå University, Faculty of Science and Technology, Department of Physics.ORCID iD: 0000-0002-3881-6764
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Carbon nanotubes are carbon based structures with outstanding electronical and mechanical properties. They are used in a wide range of applications, usually embedded in polymer in the form of composites, in order to affect the electronic behavior of the matrix material. However, as the nanotubes properties are directly dependent on their intrinsic structure, it is necessary to select specific nanotubes depending on the application, which can be a complicated and inefficient process. This makes it attractive to be able to reduce the amount of material used in the composites.

In this thesis, focus is placed on the electrical properties of the composites. A simple patterning method is presented which allows the use of extremely low amounts of nanotubes in order to increase the electrical conductivity of diverse polymers such as polystyrene (PS) or poly(3-hexylthiophene) (P3HT). This method is called nanoimprint lithography and uses a flexible mold in order to pattern composite films, leading to the creation of conducting nanotube networks, resulting in vertically conducting samples (from the bottom of the film to the top of the imprinted patterns).

In parallel, X-ray diffraction measurements have been conducted on thin P3HT polymer films. These were prepared on either silicon substrate or on graphene, and the influence of the processing conditions as well as of the substrate on the crystallinity of the polymer have been investigated. The knowledge of the crystalline structure of P3HT is of great importance as it influences its electronic properties. Establishing a link between the processing conditions and the resulting crystallinity is therefore vital in order to be able to make opto-electronic devices such as transistor or photovoltaic cells.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2016. , 57 p.
Keyword [en]
carbon nanotubes, polythiophene, electrical conductivity, crystallography, graphene, nanoimprint lithography, synchrotron diffraction
National Category
Nano Technology
Research subject
Physics
Identifiers
URN: urn:nbn:se:umu:diva-119779ISBN: 978-91-7601-478-3 (print)OAI: oai:DiVA.org:umu-119779DiVA: diva2:926487
Public defence
2016-06-01, KB3B1, KBC, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2016-05-11 Created: 2016-04-27 Last updated: 2016-05-26Bibliographically approved
List of papers
1. Nanostructured networks of single wall carbon nanotubes for highly transparent, conductive, and anti-reflective flexible electrodes
Open this publication in new window or tab >>Nanostructured networks of single wall carbon nanotubes for highly transparent, conductive, and anti-reflective flexible electrodes
2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 2, 021116Article in journal (Refereed) Published
Abstract [en]

Highly transparent, anti-reflective, flexible, and conductive electrodes are produced by nanopatterning of a polymer composite made of single wall carbon nanotubes (SWNTs). The formation of nanostructures creates interconnected nanotubes and vertically aligned SWNT networks which greatly improves charge transport compared to a traditionally mixed composite. These electrodes moreover possess high transparency (98% at 550 nm) and good anti-reflective properties. The use of low nanotube loadings provides an economical solution to make conductive and highly transparent flexible electrodes. The process used is simple and can be easily scaled to large areas by roll to roll processes.

National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-79425 (URN)10.1063/1.4813498 (DOI)000321761000016 ()
Available from: 2013-09-03 Created: 2013-08-19 Last updated: 2017-12-06Bibliographically approved
2. Nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading
Open this publication in new window or tab >>Nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading
2014 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 26, no 19, 3111-3117 p.Article in journal, Letter (Refereed) Published
Abstract [en]

We demonstrate a simple and controllable method to form periodic arrays of highly conductive nano-engineered single wall carbon nanotube networks from solution. These networks increase the conductivity of a polymer composite by as much as eight orders of magnitude compared to a traditional random network. These nano-engineered networks are demonstrated in both polystyrene and polythiophene polymers.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
Keyword
carbon nanotube networks;nano-engineering;charge transport;organic electronic devices;nanoimprinting
National Category
Nano Technology
Identifiers
urn:nbn:se:umu:diva-89132 (URN)10.1002/adma.201305843 (DOI)000335869100023 ()
Available from: 2014-05-22 Created: 2014-05-22 Last updated: 2017-12-05Bibliographically approved
3. SWNT nano-engineered networks strongly increase charge transport in P3HT
Open this publication in new window or tab >>SWNT nano-engineered networks strongly increase charge transport in P3HT
2014 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 6, no 20, 11633-11636 p.Article in journal, Letter (Refereed) Published
Abstract [en]

We demonstrate the formation of arrays of 3D nano- sized networks of interconnected single-wall carbon nanotubes (SWNT) with well defined dimensions in a poly-3- hexylthiophene (P3HT) thin film. These novel nanotube nano-networks produce efficient ohmic charge transport, even at very low nanotube loadings and low voltages. An increase in conductivity between one and two orders of magnitude is observed compared to a random network. The formation of these nano-engineered networks is compatible with large area imprinting and roll to roll processes, which makes it highly desirable for opto-electronic and energy conversion applications using carbon nanotubes.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2014
National Category
Nano Technology
Identifiers
urn:nbn:se:umu:diva-89131 (URN)10.1039/C4NR01542H (DOI)000343000800005 ()
Available from: 2014-05-22 Created: 2014-05-22 Last updated: 2017-12-05Bibliographically approved
4. Ordered and Highly Conductive Carbon Nanotube Nano-Networks in a emiconducting Polymer Film by Solution Processing
Open this publication in new window or tab >>Ordered and Highly Conductive Carbon Nanotube Nano-Networks in a emiconducting Polymer Film by Solution Processing
2015 (English)In: Advanced Electronic Materials, ISSN 2199-160X, Vol. 1, no 5, 1400030Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:umu:diva-107101 (URN)10.1002/aelm.201400030 (DOI)000357655700002 ()
Available from: 2015-08-31 Created: 2015-08-18 Last updated: 2016-05-11Bibliographically approved
5. Enhanced Vertical Charge Transport in a Semiconducting P3HT Thin Film on Single Layer Graphene
Open this publication in new window or tab >>Enhanced Vertical Charge Transport in a Semiconducting P3HT Thin Film on Single Layer Graphene
Show others...
2015 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 25, no 5, 664-670 p.Article in journal (Refereed) Published
Abstract [en]

The crystallization and electrical characterization of the semiconducting polymer poly(3-hexylthiophene) (P3HT) on a single layer graphene sheet is reported. Grazing incidence X-ray diffraction revealed that P3HT crystallizes with a mixture of face-on and edge-on lamellar orientations on graphene compared to mainly edge-on on a silicon substrate. Moreover, whereas ultrathin (10 nm) P3HT films form well oriented face-on and edge-on lamellae, thicker (50 nm) films form a mosaic of lamellae oriented at different angles from the graphene substrate. This mosaic of crystallites with - stacking oriented homogeneously at various angles inside the film favors the creation of a continuous pathway of interconnected crystallites, and results in a strong enhancement in vertical charge transport and charge carrier mobility in the thicker P3HT film. These results provide a better understanding of polythiophene crystallization on graphene, and should help the design of more efficient graphene based organic devices by control of the crystallinity of the semiconducting film.

Keyword
graphene, organic semiconductor, P3HT, crystallization, charge transport
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:umu:diva-100760 (URN)10.1002/adfm.201403418 (DOI)000349225400001 ()
Available from: 2015-04-26 Created: 2015-03-09 Last updated: 2017-12-04Bibliographically approved
6. Reduced crystallinity and enhanced charge transport by melt annealing of an organic semiconductor on single layer graphene
Open this publication in new window or tab >>Reduced crystallinity and enhanced charge transport by melt annealing of an organic semiconductor on single layer graphene
Show others...
2016 (English)In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 4, no 19, 4143-4149 p.Article in journal (Refereed) Published
Abstract [en]

We report on the effect of the annealing temperature on the crystallization and the electrical properties of the semiconducting polymer poly(3-hexylthiophene) (P3HT) on single layer graphene. Electrical characterization showed that heating the P3HT film above the melting point (Tm) resulted in a higher vertical charge carrier mobility. Grazing incidence X-ray diffraction (GIXD) revealed that the film was actually less crystalline overall, but that it consisted of a much higher number of face-on crystallites. We moreover show that annealing above Tm removes the existing seeds still present in the film at lower temperatures and enhances face-on formation. These results provide a better understanding of the influence of the annealing temperature on polythiophene crystallization on graphene, and it shows that the annealing at higher temperature induces a more favorable crystalline orientation which enhances charge transport, despite the reduction in the overall crystallinity. These results should help in the design of more efficient graphene based organic electronic devices by controlling the crystalline morphology of the semiconducting film.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:umu:diva-120203 (URN)10.1039/C6TC00625F (DOI)000376041700006 ()
Available from: 2016-05-11 Created: 2016-05-11 Last updated: 2017-11-30Bibliographically approved

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