Charge Transport in Highly Face-On Poly(3-hexylthiophene) Films

• Published in: Journal of physical chemistry. C Vol. 117; no. 34; pp. 17421 - 17428
• Main Authors: Gargi, Deepak, Kline, R. Joseph, DeLongchamp, Dean M., Fischer, Daniel A., Toney, Michael F., O’Connor, Brendan T.
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 29.08.2013
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Electronics; Exact sciences and technology; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Transistors; Stacking sequence; XANES; X-ray spectra; Charge transport; XRD; Thin film transistors; Thin films; Thiophene derivative polymer; Anisotropy; Strained layer; High field; Organic semiconductors; Ultraviolet visible spectrum; Transport processes; Microstructure; Crystal structure
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp4050644

We report that the π-stacking direction in poly(3-hexylthiophene) (P3HT) films can be made to orient strongly out-of plane by uniaxially straining films in orthogonal directions, providing a valuable opportunity to evaluate charge transport in a very unusual microstructure for this material. The structure of the films was characterized using UV–visible spectroscopy, X-ray diffraction, and near-edge X-ray absorption fine structure spectroscopy, showing that unstrained films have a weakly edge-on stacking character with a large orientation distribution, whereas films strained biaxially by 100% in orthogonal directions have highly face-on stacking. In the biaxially strained films the face-on packing occurs while the P3HT long axis orientation is found to be only weakly anisotropic in-plane. Charge transport is characterized in an organic thin-film transistor (OTFT) configuration, showing that the saturated field effect mobility in the biaxially strained films is greater than that for unstrained films for channel lengths ≤10 μm. The mobilities are found to have different channel-length dependence, attributed primarily to differences in the field-dependent charge-transport behavior, resulting in the mobility being comparable for channel lengths of 20 μm. The results suggest that edge-on packing is not a prerequisite for relatively high-field-effect mobility in P3HT-based OTFTs.