Project A5: Controlled nucleation and growth of conjugated polymers via chemically and topographically patterned surfaces
Principal Investigators: M.Sommer (Freiburg) / M. Brinkmann (Strasbourg)
PhD Student: Rukiya Matsidik
Current state of the research
Conjugated polymers, in particular regioregular poly(alkylthiophenes) (P3ATs), are nowadays key materials both for photovoltaic applications and organic field effect transistors because of their semiconducting behavior and unique charge transport properties obtained for highly crystalline systems. One main problem that remains is the precise control of the nucleation and growth of these semicrystalline systems to improve device performance.
Although considerable efforts have been made to study the crystallization of P3ATs in spincoated thin films, numerous aspects are still open [1]. For instance, the control of the nucleation on oriented and patterned surfaces has not been explored thoroughly so far. However, nucleation can be triggered by specific surfaces bearing intrinsic similarity at the molecular scale with P3AT and acting as templates for epitaxial growth. This has been demonstrated, for example, by Ihn and Smith [2] by heterogeneous nucleation of poly(3-hexylthiophene) (P3HT) using the lateral edges of an oriented single crystal of polyethylene.
We will address the possibility to induce crystallization and nucleation at specific locations on surfaces.
Contributions of the participating groups
The Brinkmann group has thorough experience in: (i) morphogenesis of conjugated polymers and small molecules using epitaxial growth [3] and (ii) structure determination of various conjugated polymers (regioregular polythiophenes and polyfluorenes) based on transmission electron microscopy including electron diffraction [4]. Recent research activities focus on hybrid systems comprising semiconducting polymers and inorganic nanoparticles (CdSe) to obtain highly oriented and nanostructured thin films suitable for photovoltaic applications [5].
In the Ludwigs group electroactive polymers, e.g. polythiophenes, are synthesized and characterized by physicochemical methods, such as electrochemistry [6], spectroscopy and charge transport measurements. Moreover, the group has expertise in various soft-lithographic top-down [7] and bottom-up [8] methods for patterning on the micrometer and nanometer scales. The collaboration with the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg could be implemented at the end of the project to test the new developed processes in real device applications.
References
[1] Kline, R. J.; McGehee, M. D.; Kadnikova, E. N.; Liu, J.; Fréchet, J. M. J.; Toney, M. F. Macromolecules 2005, 38, 3312.
[2] Ihn, K. J.; Smith, P. Bulletin of the Institute for Chemical Research, Kyoto University, 1991, 69(2), 111.
[3] Pratontep, S.; Brinkmann, M.; Nüesch, F.; Zuppiroli, L. Phys. Rev. B 2004, 69, 165201.
[4] Brinkmann, M.; Charoenthai, N.; Traiphol, R.; Piyakulawat, P.; Wlosnewski, J.; Asawapirom, U. Macromolecules 2009, 42, 8298.
[5] Brinkmann, M.; Aldakov, D.; Chandezon, F. Adv. Mat. 2007, 19, 3812.
[6] Heinze, J.; Frontana-Uribe, B.; Ludwigs, S. The electrochemistry of conducting polymers. Persistent models, new concepts, Chemical Reviews, 2010 asap.
[7] Voicu, N. E.; Ludwigs, S.; Crossland, E. J. W.; Andrew, P.; Steiner, U. Adv. Mater. 2007, 19, 757.
[8] Ludwigs, S.; Böker, A.; Voronov, A.; Rehse, N.; Magerle, R.; Krausch, G. Nature Mater. 2003, 2, 744. Crossland, E. J. W.; Nedelcu, M.; Ducati, C.; Ludwigs, S.; Hillmyer, M.; Steiner, U.; Snaith, H. Nano Lett. 2009, 9, 2813.