Simple approach to prepare nanostructured donor/acceptor interfaces for photovoltaic applications (invited)_abstract only, Proc International Conf. on Advanced Polymeric Materials - ICAPM, Kottayam, India, Vol. na, pp. na - na, October, 2013.
Simple approach to prepare nanostructured donor/acceptor interfaces for photovoltaic applications
Instituto de Telecomunicações and Departament of Bioengineering, Instituto Superior Técnico, UTL, Av. Rovisco Pais, P-1049-001 Lisboa, Portugal
The progress in organic photovoltaics (OPVs), namely those based on polymer blends or polymer composites, has been supported by both the development of new materials and control of their nano/microstructure. Relying on electron-donor/electron-acceptor combinations to efficiently split the excited states into charges, the OPVs final efficiency is strongly dependent on the interfacial area between the donor and acceptor domains and the creation of selective percolation paths for the photogenerated charges. The simple blending of the two components (bulk heterojunction, BHJ, architectures) is quite simple but with difficult control on the final nano/microstructure. The ideal active layer structure would consist on a donor/acceptor bi-layer with an interdigitated-like interface formed by columns, whose diameters should be on the order of 20 nm. Though the confirmation of this proposal has been demonstrated using a double nanoimprint process, there is no simple method yet, that could be scaled up to large areas, able to provide such nanostructures.
Our group has devoted a significant effort over the last years in the optimization of a phase separation process that could provide such nanostructured D/A interfaces . This method relies on the phase separation occurring in blends of conjugated polymers and polystyrene upon spin coating. Fortunately, a pure PS phase is formed on top, with a columnar-like interface with the underlying conjugated polymer. The key issue in the process we have developed is the use of cross-linkable conjugated polymers. This additional functionality is brought about by the introduction of oxetane side groups, which can undergo a ring opening polymerisation, leading to the formation of a insoluble network. This allows not only the removal of PS upon rinsing with an adequate solvent but also the subsequent deposition of the electron acceptor on top, by spin coating.
In this presentation, I will discuss the details of materials preparation and characterization and review our efforts to fabricate OPVs with D/A nanostructured interfaces based on the various oxetane-functionalised conjugated polymers we have prepared.
Acknowledgments. This work was partially financed by FCT-Portugal under the contracts PTDC/CTM-NAN/111263/2009, PTDC/CTM/101627/2008 and PEst-OE/EEI/LA0008/2013.
 X. He, F. Gao, G. Tu, D. G. Hasko, S. Hüttner, N. C. Greenham, U. Steiner, R. H. Friend, W.T.S. Huck, Adv. Funct. Mater. 2011, 21, 139.
a) J. Farinhas, Q. Ferreira, R.E. Di Paolo, L. Alcácer, J. Morgado, A. Charas, J. Mater. Chem. 2011, 21, 12511. b) G. Brotas, J. Farinhas, Q. Ferreira, J. Morgado, A. Charas, Synth. Met. 2012, 162, 2052.