Conjugated polymers exhibit optoelectronic properties comparable with those inorganic semiconductors and with the advantage of lower cost of production to recover large areas in thin films from solutions by conventional deposition techniques. By their side, carbon nanotubes (CNTs) offer a great opportunity for exciton dissociation, because of their high surface area and different work function comparing with the polymers. For this reason, the combination of conjugated polymer and CNTs in composites has garnered interest in recent advances for solar cells technology. In this work we present a study on nanocomposites based on a poly(phenyleneetynylene) sequenced with thioester moieties (pPET3Oc12-sqS) with single (SWCNTs) and multiwall (MWCNTs) CNTs in order to develop novel materials for photovoltaic devices.
The 1NMR analysis suggest π stacking between the rigid conjugated backbone of the polymer and the backbone of the nanotubes on the basis of the high broadening of the phenylene protons peaks of both, the tioester-ethyldisulfide and the α, β and γ-O-CH2- chains of pPET3OC12-sqS, wich practically disapear and likely due to the fact that these spins need more relaxation time to show signals. The optical band gap decreases in the nanocomposites, suggesting an enhancement of the electrical conductivity as confirmed by cyclic voltammetry and by electrical measurements, where the electrical conductivity of the composites resulted one order of magnitude higher than of pPET3OC12-sqS. A quenching of the polymer fluorescence is found, which is attributed to the efficient energy transfer between pPET3OC12-sqS and CNTs, more than the disruption of conjugation by a conformational change and in agreement with the fact that the absorption and emission maxims are unchanged. Micrographs of SEM and TEM indicate a good dispersion of the nanotubes in the polymer matrix as well as the absense of bundles of nanotubes in the composite which is consistent with a homogeneous adhesion of the pPET3OC12-sqS around the CNTs.
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