Abstract's Details

Microstructure Study of Anisotropic Polythiophene Thin Films for Trap Distribution Correlations
Abstract ID	MAT-04
Presenter	Leslie Jimison
Presentation Type	Poster
Full Author List	L. Jimison (1), M. F. Toney (2), A. Salleo (1)
Affiliations	(1) Stanford University (2) Stanford Synchrotron Radiation Laboratory
Category	Materials Science
Abstract	Recently, there has been considerable interest in the development of semiconducting polymers for use in printable electronic devices, such as transistors for display backplanes.¹ These materials offer a cost effective alternative to conventional semiconductors, with key advantages of organic materials being their low processing temperature and possibility of solution processing in ambient, enabling roll-to-roll fabrication. In semiconducting polymers, device performance is strongly dependent on film microstructure, however, the correlation between the two is not yet fully understood. Conjugated polymers generally form a semicrystalline microstructure, consisting of lamellar crystalline regions separated by amorphous grain boundaries. We have used a means of controlling the orientation and size of crystallites² in the plane of the substrate to explore the relationship between trap density within grain boundaries and charge transport. Regioregular poly-3-hexylthiopene (P3HT) is the material under investigation. We have fabricated anisotropic films on glass and silicon substrates by taking advantage of the needle-like growth of 1,3,5-tricholorobenzene (TCB). We use TCB first as a solvent at a high temperature and then as a nucleating agent and substrate for epitaxy once cooled. When TCB is removed from the P3HT/TCB film, an oriented single-component polymer film is left behind, consisting of large (mm²) domains where the film extinguishes uniformly under crossed polarizers, suggesting long range orientation of the polymer chain axis. The microstructure of the resulting films was characterized at the Stanford Synchrotron Radiation Laboratory. Grazing incidence diffraction patterns collected with an area detector (Beamline 11-3) reveal out-of-plane texture of the pi-stacking direction. Grazing incidence patterns collected at orthogonal values of phi with a high resolution point detector (Beamline 7-2) quantify the extent of anisotropy of the orientation of the polymer chains. Diffraction data has also been collected that suggests the rotation of polymer chains on annealing; useful for thin film transistor fabrication. Complimentary characterization with atomic force microscopy reveals the lamellar structure of the polymer crystallites. Charge transport in the directionally crystallized films was probed by measuring in plane mobilities using thin film transistors with the oriented film as the active layer. Transport measurements as a function of charge density and temperature was used to explore the effect of microstructure on trap distribution.
Footnotes	Dimitrakopoulos, Adv. Mat. v.14, 2 (2002) Brinkmann, Adv. Mat. 18 (2006)
Funding Acknowledgement