Macroscopic alignment of poly(3‐hexylthiophene) for enhanced long‐range collection of photogenerated carriers

• Published in: Journal of polymer science. Part B, Polymer physics Polymer physics, 2016-01, Vol.54 (2), p.180-188
• Main Authors: Li, Anton, Bilby, David, Dong, Ban Xuan, Amonoo, Jojo, Kim, Jinsang, Green, Peter F
• Format: Article
• Language: English
• Subjects: Alignment; Anisotropy; atomic force microscopy; butyric acid; Carriers; charge transport; conjugated polymers; fibers; Lasers; morphology; polymers; processing; Semiconductor devices; solar cells; solvents; Spots; Strategy; Thin film transistors
• ISSN: 0887-6266; 1099-0488
• DOI: 10.1002/polb.23888

An epitaxy‐directing solvent additive 1,3,5‐trichlorobenzene is combined with an off‐center spin‐casting technique to produce poly(3‐hexylthiophene) (P3HT) fibers with uniaxial in‐plane alignment on the centimeter scale. Photoconductive atomic force microscopy (pc‐AFM) is used to characterize planar heterojunction devices assembled from phenyl‐C₆₁ butyric acid methyl ester (PCBM) acceptor and both aligned and unaligned P3HT donor. By varying the relative positions of the laser spot (site of carrier generation) and probe (site of hole extraction), it is found that devices with aligned P3HT exhibit anisotropic and greatly enhanced long‐range photocarrier transport, with nearly 10% of original photocurrent measured 400 µm from the laser spot along the direction parallel to the alignment. Complementary thin film transistor (TFT) measurements reveal a factor of ∼3.5 difference in the hole mobilities parallel and perpendicular to the direction of alignment. Together, these findings highlight the importance of macroscopic alignment as a strategy to overcome the low mobilities of disordered polymer semiconductors.1 © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 180–188