Published online by Cambridge University Press: 02 March 2011
Classical molecular dynamics (MD) simulations in conjunction with opticalabsorption and AFM/nano-Raman experiments are employed to relate themolecular-scale arrangement and conjugation of poly-3-hexylthiophene (P3HT)adsorbed onto single-walled carbon nanotubes (SWNTs) and multi-walled carbonnanotubes (MWNTs). Taken together our results demonstrate the templatingrole of carbon nanotubes in increasing the π-conjugation length of the P3HTat the P3HT/carbon nanotube interface. The MD simulations show that SWNTsand MWNTs, due to their inherent 1-dimensional (1D) cylindrical shape andπ-conjugation, planarize the P3HT molecules adsorbed at their surface andthus quench their torsional disorder, regardless of the P3HT conformationand nanotube chirality. This effect is more significant for higher SWNTweight fractions in the sample (since it is an interface effect). Weinvestigated this effect experimentally by acquiring nano-Raman spectra inregions of high-MWNT/low-P3HT content in addition to optical absorptionspectra of P3HT-SWNT composites with different SWNT concentrations . Theincrease in the P3HT conjugation is confirmed by a shift of a P3HT featurein the Raman spectrum when going from P3HT-rich to SWNT-rich areas in themixture. The significance of this work for charge transfer at the P3HT-SWNTinterface in bulk-heterojunction solar cells is discussed.