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ABSTRACT Charge transport in poly(3-alkylthiophene)s (P3AT)s is closely linked to the nanoscale organization of crystallites. Block copolymer morphologies provide an ideal platform to study crystallization as the chain ends are tethered at a known interface in a well-defined geometry. The impact of soft versus hard confinement on P3EHT crystallization was studied using poly(3-(2′-ethyl)hexylthiophene) (P3EHT) containing diblocks with both rubbery poly(methyl acrylate) (PMA) and glassy polystyrene (PS) blocks. Here, P3EHT's lower melting point relative to the commonly studied poly(3-hexylthiophene) (P3HT) facilitated its confined crystallization and makes it an ideal model system. While transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) revealed well-ordered lamellar morphologies both in the melt and post-crystallization for both sets of diblocks, the glassy blocks inhibit confined crystallization of P3EHT relative to rubbery matrix blocks. Analysis of aligned diblocks by both SAXS and wide angle X-ray scattering (WAXS) revealed that the P3EHT chain axis aligns perpendicular to domain interfaces, allowing preferential growth of the alkyl-chain and π-π stacking directions parallel to lamellae. Finally, it was shown that following diblock self-assembly in the melt, crystallite growth drives expansion of microdomains to match the P3EHT contour length. It was concluded that P3EHT chains adopted an extended conformation within confined crystallites due to the rigid nature of polythiophenes relative to flexible chain crystalline polymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 205-215 [ABSTRACT FROM AUTHOR]

In this work, crystallization kinetics and aggregate growth of poly(3-ethylhexylthiophene) (P3EHT) thin films are studied as a function of film thickness. X-ray diffraction and optical absorption show that individual aggregates and crystallites grow anisotropically and mostly along only two packing directions: the alkyl stacking and the polymer chain backbone direction. Further, it is also determined that crystallization kinetics is limited by the reorganization of polymer chains and depends strongly on the film thickness and average molecular weight. Time-dependent, field-effect hole mobilities in thin films reveal a percolation threshold for both low and high molecular weight P3EHT. Structural analysis reveals that charge percolation requires bridged aggregates separated by a distance of ≈2-3 nm, which is on the order of the polymer persistence length. These results thus highlight the importance of tie molecules and inter-aggregate distance in supporting charge percolation in semiconducting polymer thin films. The study as a whole also demonstrates that P3EHT is an ideal model system for polythiophenes and should prove to be useful for future investigations into crystallization kinetics. [ABSTRACT FROM AUTHOR]