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Its inherent strong tendency to aggregate in solution is used in the following study to prepare highly anisotropic films of the n-type copolymer poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)). Solvent vapor annealing (SVA) allows to tune the size of oriented domains in spherulite-like superstructures with alignment up to several hundreds of micrometers. Blade coating (BC), on the other hand, yields square centimeter large perfectly oriented films with dichroic ratios of 18 and charge transport anisotropies up to 14. On the nanometer scale highly oriented fibers of form I are visible in the oriented areas with the fiber long axis parallel to the chain direction. We give experimental evidence that structure formation does involve liquid crystal (LC) mesophases at high solution concentrations which are frozen upon solvent removal. Temperature post-treatment of the oriented films gives, on the other hand, evidence for a classical semicrystalline nature of this polymer with spherulites consisting of crystalline and amorphous domains. These findings point to a different growth behavior than previously discussed for the well-studied p-type polymer poly(3-hexylthiophene) and suggests that the definition and distinction between liquid-crystalline and semicrystalline nature might need to be reassessed.

Poly(9,9'-dioctylfluorene-co-benzothiadiazole) is known for application in LED and FET devices [1-3], although a reliable crystal structure has not definitely reported. Thin films of the material deposited onto different self-assembled monolayers and annealed at different temperatures, were examined by synchrotron radiation in grazing incidence and compared with optimized powder of same material. By applying the variable cell direct space method of ref. [4] to the diffraction profile obtained from the thermally optimized powders of the polymer, and combining the observations of confocal optical microscopy at different temperatures on the films, the polymorphic character of the polymer in the films was definitely assessed, in terms of a 3D phase and a mesophase form. These results allow for the accurate determination of both orientation and crystallinity of various films. Subtle differences among films deposited on surface layers displaying various polarity, namely SiOx, hexamethyldisilazane, divinyltetramethyldisiloxane-bis(benzocyclobutene), sodium poly(styrenesulphonate), could be exploited and will be addressed.

The operation of resistive switches based on phase-separated blends of organic ferroelectrics and semiconductors depends significantly on the microstructure of such systems. A wide range of analysis techniques are used to characterize spin-coated films of the ferroelectric random copolymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], and the semiconducting polymer, regio-irregular poly(3-hexylthiophene) (rir-P3HT). The blend separates into amorphous rir-P3HT domains embedded in a crystalline P(VDF-TrFE) matrix. The rir-P3HT domains are continuous throughout the film, from the substrate/blend interface to the blend/air interface. We also investigate the rir-P3HT domain size and number as a function of composition and find - unexpectedly - a rather mono-disperse domain size distribution for a given rir-P3HT:P(VDF-TrFE) ratio. The domain size increases with rir-P3HT content, indicating that the solidification is not dominated by nucleation processes. Spinodal decomposition is therefore more likely to be responsible for the microstructure induced in the rir-P3HT:P(VDF-TrFE) blends. Since spinodal decomposition occurs spontaneously without the presence of a nucleation step, this can facilitate processing considerably, since the intricate control of nucleation processes (homogenous or heterogenous) is rendered unnecessary. Measurement of the lateral conductivity of the blends demonstrates that the rir-P3HT domains are electrically not connected, supporting the microstructural evidence. A perpendicular current through the film is measured using both Au and Ag electrodes as a function of blend composition. A model was used to interpret the electrical transport. The injection for Ag diodes poled into the ON-state preferentially occurs at the circumference of the rir-P3HT domains. An accumulation width over which the injection occurs is estimated to be of the order of a few hundred nm. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The phase-separated structure of blends of the ferroelectric polymer P(VDF-TrFE) and the semiconducting polymer P3HT used in organic non-volatile memories is revealed with soft X-ray spectromicroscopy. These thin-film blends show a columnar morphology, with P3HT-rich columns enclosed in a continuous, essentially pure P(VDF-TrFE) phase favorable for data storage operation.