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Enhanced Vertical Charge Transport in a Semiconducting P3HT Thin Film on Single Layer Graphene
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
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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.

Place, publisher, year, edition, pages
2015. Vol. 25, no 5, 664-670 p.
Keyword [en]
graphene, organic semiconductor, P3HT, crystallization, charge transport
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:umu:diva-100760DOI: 10.1002/adfm.201403418ISI: 000349225400001OAI: oai:DiVA.org:umu-100760DiVA: diva2:807933
Available from: 2015-04-26 Created: 2015-03-09 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Carbon nanotubes and graphene polymer composites for opto-electronic applications
Open this publication in new window or tab >>Carbon nanotubes and graphene polymer composites for opto-electronic applications
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
carbon nanotubes, polythiophene, electrical conductivity, crystallography, graphene, nanoimprint lithography, synchrotron diffraction
National Category
Nano Technology
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-119779 (URN)978-91-7601-478-3 (ISBN)
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
2. Vertical charge transport in conjugated polymers
Open this publication in new window or tab >>Vertical charge transport in conjugated polymers
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Conjugated polymers are novel organic electronic materials highly important for organic photovoltaic applications. Charge transport is one of the key properties which defines the performance of conjugated polymers in electronic devices.

This work aims to explore the charge transport anisotropy in thin films of P3HT, one of the most common conjugated polymers. Using X-ray diffraction techniques and charge transport measurements, the relation between vertical charge transport through thin P3HT films and structure of the films was established.

It was shown that particular orientations of crystalline domains of P3HT, namely face-on and chain-on, are beneficial for vertical charge transport. These orientations provide the efficient pathways for the charges to be transported vertically, either via π-π stacking interaction between the adjacent conjugated chains, or via the conjugated chain backbones. It was also demonstrated that particular orientations of crystallites are favourable for the formation of interconnected percolated pathways providing enhanced vertical charge transport across the film.

Deposition of P3HT on most commonly used silicon substrates typically results in the formation of mostly edge-on orientation of crystallites which is unfavourable for vertical charge transport. Nanoimprint lithography was demonstrated as a powerful processing method for reorienting the edge-on crystalline domains of P3HT into chain-on (vertical) orientation. It is also shown that thin P3HT films with preferentially face-on orientations of crystallites can be deposited on graphene surface by spin coating.

Using patterning of thin P3HT films by nanoimprint lithography, unprecedentedly high average vertical mobilities in the range of 3.1-10.6 cm2 V-1 s-1 were achieved in undoped P3HT.

These results demonstrate that charge transport in thin films of a relatively simple and well-known conjugated polymer P3HT can be significantly improved using optimization of crystallinity,orientation of crystallites, polymer chain orientation and alignment in the films.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2017. 88 p.
Keyword
organic electronics, conjugated polymers, nanotechnology, nanoimprint lithography, graphene, P3HT, charge transport, X-ray diffraction, structure, crystallite orientation
National Category
Nano Technology Textile, Rubber and Polymeric Materials
Research subject
Materials Science
Identifiers
urn:nbn:se:umu:diva-133180 (URN)978-91-7601-686-2 (ISBN)
Public defence
2017-05-17, N420, Naturvetarhuset, Universitetsvägen, 901 87, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2017-04-26 Created: 2017-03-31 Last updated: 2017-04-24Bibliographically approved

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