Anisotropic Structure and Charge Transport in Highly Strain-Aligned Regioregular Poly(3-hexylthiophene)

• Published in: Advanced functional materials Vol. 21; no. 19; pp. 3697 - 3705
• Main Authors: O'Connor, Brendan, Kline, R. Joseph, Conrad, Brad R., Richter, Lee J., Gundlach, David, Toney, Michael F., DeLongchamp, Dean M.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 07-10-2011; WILEY‐VCH Verlag
• Subjects: Alignment; Anisotropy; Backbone; Charge transport; conducting polymers; Hole mobility; Mathematical analysis; organic field-effect transistors; poly(3-hexylthiophene) (P3HT); polymer alignment; Semiconductors; Strain
• ISSN: 1616-301X; 1616-3028; 1616-3028
• DOI: 10.1002/adfm.201100904

A novel method of strain‐aligning polymer films is introduced and applied to regioregular poly(3‐hexylthiophene) (P3HT), showing several important features of charge transport. The polymer backbone is shown to align in the direction of applied strain resulting in a large charge‐mobility anisotropy, where the in‐plane mobility increases in the applied strain direction and decreases in the perpendicular direction. In the aligned film, the hole mobility is successfully represented by a two‐dimensional tensor, suggesting that charge transport parallel to the polymer backbone within a P3HT crystal is strongly favored over the other crystallographic directions. Hole mobility parallel to the backbone is shown to be high for a mixture of plane‐on and edge‐on packing configurations, as the strain alignment is found to induce a significant face‐on orientation of the originally highly edge‐on oriented crystalline regions of the film. This alignment approach can achieve an optical dichroic ratio of 4.8 and a charge‐mobility anisotropy of 9, providing a simple and effective method to investigate charge‐transport mechanisms in polymer semiconductors.
A novel method of strain‐aligning polymer films is introduced and applied to the semiconducting polymer, regioregular poly(3‐hexylthiophene) (P3HT). Detailed morphological and electronic characterization is performed on the aligned film, showing several important features of charge transport. The polymer backbone is shown to align in the direction of applied strain resulting in a mobility anisotropy as high as 9. Reported results indicate that charge transport parallel to the polymer backbone within a P3HT crystal is strongly favored over the other crystallographic directions. (OTFT = organic thin‐film transistor)