Carbon nanotube containing electrodes for organic electronics applications
- Flexible transparent electrodes are critical for use in large-area or flexible touch screens, solar cells, and flat panel displays. An ideal material should be inexpensive, nontoxic, flexible, solution processable, thin and uniform, with a sheet resistance of less than 50 ohms per square at 90% transmission. No current material satisfies this set of specifications. One promising candidate is the carbon nanotube (CNT) network. There are two key challenges in making CNT electrodes. Firstly, in dispersion, van der Waals forces drive CNT aggregation into bundles, which are less efficient conductors than single tubes. Secondly, transport through a CNT network is typically dominated by large intertube resistances. The work in this thesis develops and studies composite materials addressing each of these challenges. In the first part of this thesis, we develop a method for making four-probe conductivity measurements on CNT bundles in networks, and compare these with data taken via electrostatic force microscopy. We confirm that bundles are less efficient at charge transport than single tubes, and that intertube rather than interbundle junctions limit transport in bundled networks. We then explore the use of poly-3-hexylthiophene (P3HT), as a dispersing agent for CNTs. While P3HT debundles CNTs, improves film morphology considerably and facilitates processing immensely, we find that too much P3HT can still substantially reduce the overall conductivity of the films. To improve this, and to address the tube junction resistance problem in general, the second part of the thesis focuses on p-type doping of CNTs, which increases free carrier concentration and lowers or eliminates intertube Schottky barriers. Known CNT dopants, including nitric acid and thionyl chloride, are toxic, corrosive, and/or ephemeral. We develop a new mild, stable and competitive process to dope CNT networks with molybdenum oxide, and explore the doping mechanism. We then compare this process with doping by thionyl chloride and by tetrafluorotetracyano-p-quinodimethane, a known mild molecular dopant. Lastly, to affirm the utility of these CNT composites as electrodes for organic semiconductor devices, we optimize methods to pattern them with high fidelity on dielectric surfaces and show that they can drive organic thin film transistors, in some cases better than can typical Au bottom contact electrodes.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Hellstrom, Sondra Lynn
|Stanford University, Department of Applied Physics
|Fisher, Ian R. (Ian Randal)
|Fisher, Ian R. (Ian Randal)
|Statement of responsibility
|Sondra Lynn Hellstrom.
|Submitted to the Department of Applied Physics.
|Thesis (Ph.D.)--Stanford University, 2012.
- © 2012 by Sondra Lynn Hellstrom
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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