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We report a detailed characterization of the thin film morphology of all-polymer blend devices by applying a combined analysis of physical, chemical, optical, and charge transport properties. This is exemplified by considering a model system comprising poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). We show that the interactions between the two conjugated polymer components can be controlled by pre-forming the P3HT into highly ordered nanowire structures prior to blending with F8BT, and by varying the molecular weight of the F8BT. As a result, it is possible to produce films containing highly ordered P3HT with hole mobilities enhanced by three orders of magnitude over the pristine blends. Raman spectroscopy under resonant excitation conditions is used to probe the molecular order of both P3HT and F8BT phases within the blend films and these morphological studies are complemented by measurements of photocurrent generation. The resultant increase in photocurrent is associated with the enhanced charge carrier mobilities. The complementary analytical method demonstrated here is applicable to a wide range of polymer blend systems for all applications where the relationships between morphology and device performance are of interest. [ABSTRACT FROM AUTHOR]

Organic blend thin films consisting of semiconducting poly(3-hexylthiophene) (P3HT) and insulating high-density polyethylene (HDPE) have been fabricated by novel application of a large area wire-bar coating technique in air. The microstructure of P3HT:HDPE blend films reveals a strong structural dependence on initial composition. Preferential segregation of P3HT toward the film surface is observed for all blend compositions, while P3HT (or P3HT-rich) columnar structures enclosed by HDPE (or HDPE-rich) lamellar matrix is distinctive for 50:50 (by weight) blends. The transistors fabricated with P3HT:HDPE blend films show a clear field effect behavior, exhibiting charge carrier mobilities up to 5 × 10-2 cm2/Vs, comparable to the values reported in spin-coated similar blends and of neat P3HT devices. The wire-bar coated blend films and devices are highly repeatable and spatially uniform over large areas (few cm by few cm), demonstrating the suitability of this technique for manufacturing of large area organic electronic devices. [ABSTRACT FROM AUTHOR]

Optoelectronic and charge transport properties are studied for the organic-organic semiconductor interfaces formed between polymer chains and within a polymer chain. The distinctive optoelectronic and charge transport properties seen at different organic-organic semiconductor interfaces have helped in understanding the design rules of conjugated polymers required for improved molecular electronics.

We report detailed studies of optoelectronic and charge transport properties at the organic-organic semiconductor interfaces formed between polymer chains (interchain) and within a polymer chain (intrachain). These interfaces are fabricated using poly(9,9-di-n-octylfluorene-alt-N-(4-butylphenyl)diphenylamine) (TFB [f8-tfb]) (electron-donor) and poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT [f8-bt]) (electron-acceptor) conjugated polymers, by blending them together or by covalently attaching them via a main polymer backbone (copolymer). For optoelectronic properties, when a bulky and twisted tfb molecule is incorporated into a rigid F8BT conjugated backbone, it disturbs the conjugation of F8BT polymer, leading to a blue-shift in the lowest absorption transition. However, by acting as an effective electron donor, it assists the formation of an intrachain singlet exciton that has a strong charge-transfer character, leading to a red-shifted and longer-lived emission than that of F8BT. An extremely efficient and fast energy transfer from tfb donor to bt acceptor is observed in the copolymer (<1 ps) compared to transfer from TFB to F8BT in the blend (tens of ps). This efficient energy transfer in the copolymer is found to be associated with its low fluorescence efficiency (40-45% vs 60-65% for blend) because of the migration of radiative singlet excitons to low-energy states such as triplet and exciplex states that are nonemissive or weakly emissive. The presence of molecular-scale tfb-f8-bt interfaces in the copolymer, however, does not hinder an efficient transport of charge carriers at high drive voltages. Instead, it provides a better balance of charge carriers inside the device, which leads to slower decay of the device efficiency and thus more stable light-emitting diodes with increasing voltage than the blend devices. These distinctive optoelectronic and charge transport properties observed at different organic-organic semiconductor interfaces will provide useful input for the design rules of conjugated polymers required for improved molecular electronics.