We report on the synthesis and characterisation of new cross-linkable poly(3-hexylthiophene)s (X-P3HTs) and their use in the fabrication of bilayer organic photovoltaic cells (OPVs) with nanostructured interfaces. The new polymers contain regioregular blocks of 3-hexylthiophene copolymerised with oxetane-functionalized monomers (cross-linkable unit) and non-substituted thienyl units (thiophene, 2,2´-bithiophene or thieno-[3,2-b]thiophene). Nanostructured films of the new P3HTs were prepared through a process consisting on the phase separation in their blend solutions with polystyrene, which occurs during the film formation by spin coating [Farinhas J. et. al. “Nanostructured donor/acceptor interfaces in photovoltaic cells using columnar-grain films of a cross-linked poly(fluorene-alt-bithiophene)”, Journal of Materials Chemistry 21, 33 (2011), 12511-12519]. A photo-acid generator, added to the blends, catalyses the selective cross-linking of the polythiophenes, forming an insoluble network, which, in a first step, allows the removal of the polystyrene and then the PCBM deposition from solution. OPVs were fabricated from these structures. We aim at evaluating the effect of nanostructuring of the P3HT/PCBM interface on the cells performance and compare it with the performance of bulk heterojunction cells prepared with the same components. To the best of our knowledge, this work is pioneering in utilizing oxetane-functionalized polythiophenes in OPVs.
Acknowledgements: FCT Portugal (under contracts SFRH/BD/62130/2009 and PTDC/CTM-NAN/111263/2009) and Instituto de Telecomunicações (under contract PEst-OE/EEI/LA0008/2011).