Solution-processing of organic semiconductors for field-effect transistors
- Solution-processability is a key advantage of organic semiconductors, enabling us to easily deposit these materials at low-cost. Among organic semiconductors, small molecule semiconductors are typically highly crystalline and thus exhibit high carrier mobilities; however, small molecules are generally difficult to deposit into uniform films by solution-processing. In this thesis, we focus on developing solution-processing methods for semiconducting small molecules and understanding the mechanism behind film formation / charge transport in these systems for applications in organic field-effect transistors (OFETs). First, a modified capillary force lithography (MCFL) technique is introduced for fabricating highly textured micro-patterns of a crystalline semiconducting small molecule, C8-BTBT. As this technique is based on soft lithography, various geometries can be patterned onto substrates of interest and the size of the patterns is also easily controlled. Detailed characterizations reveal that the walls of the PDMS stamp used for patterning play an important role in controlling nucleation and growth of C8-BTBT crystals. Fabricated micro-line patterns for high-performance active layers in OFETs are shown to exhibit field-effect mobilities as high as 2.6 cm2/Vs. Secondly, blending semiconducting small molecules with polymer binders is investigated for simultaneously utilizing the exceptional electronic property of small molecules and the good film-forming property of polymers. Our results reveal that residual solvent in blend films following spin-coating plays a critical role in inducing vertical phase separation. In addition, we deduce specific characteristics of polymer binder that are required to generate vertical phase separation and show how annealing temperature affects the type of crystalline phase of rubrene formed in blend films. Lastly, solvent effects are also investigated on the properties of rubrene small molecule blended with a polymer binder. The properties of blend films are analyzed in terms of morphology, crystallinity, and charge transport with various characterization techniques. From our results, we found that there exists a strong correlation between the properties of blend films and solvent characteristics such as solubility, boiling temperature, and surface tension.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Jo, Pil Sung
|Stanford University, Department of Materials Science and Engineering.
|McIntyre, Paul Cameron
|McIntyre, Paul Cameron
|Statement of responsibility
|Pil Sung Jo.
|Submitted to the Department of Materials Science and Engineering.
|Thesis (Ph.D.)--Stanford University, 2014.
- © 2014 by Pil Sung Jo
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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