Self assembly of amphiphilic conjugated polyelectrolytes and nanostructured composite materials for optoelectronic applications.

摘要

Conjugated polymers (CPs) hold great promise for low cost, widely applicable optoelectronic devices such as sensors, light emitting devices, photovoltaic cells, batteries, and transistors. Although they have started to appear in the commercial marketplace, applications are still hampered by limited charge carrier mobilities of CPs in the solid state, largely because of the amorphous structure of most polymer films. We have addressed this problem by designing facially amphiphilic conjugated polyelectrolytes (CPEs) which self assemble in solution to form wormlike or cylindrical micelles. This enables control over the conformations of the polymer chains and the interactions between them. Solution phase studies of visible light and X-ray scattering confirm the presence of cylindrical aggregates, and optical spectroscopy reveals that the self-assembled polymers are in elongated conformations with minimal interchain electronic communication, due to geometrical packing and/or electrostatic repulsions between charged side chains.;The CPE micelles formed in solution can be preserved when cast on substrates as thin films, with rodlike particles observable with atomic force microscopy. By varying the conditions of film formation, the degree of interaction between polymers can be controlled. At high enough concentrations, aqueous solutions of some CPEs form hydrogels, opening the possibility for a conductive network in three dimensions. These gels also have interesting rheological properties similar to those of other wormlike micelle systems such as surfactants and structural biopolymers.;In a process similar to that developed for conventional surfactants, we have also used these polymers as structure-directing templates in a single step synthesis of nanostructured composite materials with optoelectronic functionality. This results in hybrid materials (bulk and/or thin film) with ordered arrays of nanoscale polymer domains surrounded by a framework of inorganic material such as silica, titania, or other semiconducting materials. By incorporating the polymers in spatially confined linear domains, the control over conformation and interchain interactions can be maintained in the solid state. This diversity of materials demonstrates that CPEs have great potential as active components in optoelectronic devices with tunable properties.