The performance of organic photovoltaic devices (OPVs) depends critically on the simultaneous control of the optoelectronic properties and nanoscale morphology of conjugated polyelectrolytes (CPEs).1 It is well-understood that efficient charge injection and transport in OPV devices are facilitated by a nanostructured, interpenetrating network at the active interface.2 Recently, self-assembly strategies have emerged as an elegant approach for the design and fabrication of reproducible nanoscale aggregates from CPE building blocks.3 Solvent-mediation and co-assembly with oppositely charged species are both attractive methods to control CPE architectures in solution. The challenge, however, is to determine the key structure-property relationships in these novel materials and demonstrate how tailoring the structural order in solution will be harnessed to deliver highly efficient OPV devices. Here we will demonstrate the solvent-mediated (methanol, water and methanol/water mixtures) and surfactant-mediated (SDS, d25-SDS and PFOS) self-assembly of a series of amphiphilic diblock copolymers each containing a hydrophobic poly(3-hexylthiophene) (P3HT) block and a hydrophilic cationic P3HT block bearing different terminal ionic groups.4 Their optical properties and aggregate structures have been studied in solution, and in subsequently prepared thin films, using photoluminescence (PL), scattering and microscopic techniques. We will demonstrate how a variety of well-defined, solution-phase and thin-film structures (e.g. spheres, rods, lamellar sheets) can be generated through careful modulation of the solvent polarity and surfactant charge ratio. In addition, direct comparison between the diblock copolymers and their analogous homopolymers has revealed the significance of the hydrophobic P3HT block in controlling aggregate morphology. Solvent- and surfactant mediated self-assembly of all-conjugated block CPEs may therefore provide a simple, inexpensive route to nanostructured active interfaces suitable for OPV cells. References 1 He, M.; Wang, M.; C. Lin C.; Lin Z. Nanoscale 2014, 6, 3984. 2 Vandewal, K.; Himmelberger, S.; Salleo, A. Macromolecules 2013, 46, 6379. 3 Evans, R. C. J. Mater. Chem. C 2013, 1, 4190. 4 Thomas, A.; Houston, J. E.; Van den Brande, N.; De Winter, J.; Chevrier, M.; Heenan, R. K.; A. E. Terry, A. E.; Richeter, S.; Mehdi, A.; Van Mele, B.; Dubois, P.; Lazzaroni, R.; Gerbaux, P.; Evans, R. C.; Clément, S. Polym. Chem. 2014, 5, 3352.

Solvent- and surfactant-mediated self-assembly of diblock polythiophene copolyelectrolytes for organic photovoltaic devices

251st National Meeting (2016)

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