Complexes of conjugated polymer and carbon nanotubes: does blending with nanotubes influence the ordering of semi-crysta
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Complexes of conjugated polymer and carbon nanotubes: does blending with nanotubes influence the ordering of semi-crystalline polymers? Roland G. S. Goh1, Eric R. Waclawik2, Nunzio Motta1, John M. Bell1 1 Centre for Built Environment and Engineering Research, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, AUSTRALIA 2 School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, AUSTRALIA
ABSTRACT A detailed study of poly(alkylthiophene) self-assembly and organization on single-walled carbon nanotubes is presented. We show that ordered polymer domains are formed when a conjugated polymer is blended with small amounts of carbon nanotubes. By correlating the lowest energy feature in the absorption spectra of the polymer with ordering, we demonstrate that the degree of ordering in the polymer is enhanced when it is blended with carbon nanotubes. Furthermore, we elucidated the conformation of the polymer chain when it is absorbed onto the nanotube surface and imaged the high degree of ordering in the polymer/carbon nanotube complex by microscopy.
INTRODUCTION The non-covalent functionalization of carbon nanotubes (CNT) by wrapping with polymers and through absorption of aromatic π-conjugated molecules on the nanotube sidewalls is a proven technique to solubilise carbon nanotubes in solvents and to build functional composite materials [1-3]. This facile approach to functionalizing CNTs has been used by several groups to incorporate desired functionalities on the CNTs to take advantage of their remarkable electronic and mechanical properties [4-13]. The semi-crystalline structure of poly(3hexylthiophene) (P3HT) had been studied extensively[14, 15]. A direct consequence of the highly ordered structure of P3HT is its remarkable hole mobility[15], and has led to a flurry of research activity to exploit them for organic electronic devices such as photovoltaic cells[16, 17] and field effect transistors[15, 18, 19]. In the former, P3HT is usually blended with an appropriate electron acceptor to effect charge carrier separation following photoexcitation; these includes various fullerene derivatives, carbon nanotubes as well as semiconductor nanocrystals and nanorods. Phenomenologically, photovoltaic efficiencies improve with smaller phase segregation in the blend, this has been attributed to the formation of more interfaces where exciton dissociation can occur[17]. In fact several groups working on blends of poly(alkyl-thiophene) and fullerene derivatives, have reported that increasing the percentage of fullerene derivatives in P3HT destroys the selforganized structure in P3HT [20, 21]. It has also been demonstrated that the reduced selforganization of P3HT with high amounts of fullerene leads to decreased external quantum efficiencies in organic solar cells made from composites of these materials[22]. Moreover, hole
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mobilities of p-type conjugated polymers are also known to decrease with increasing fullerene content [23
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