Abstract
Thermoelectric (TE) measurements were compared for iodine-doped composites of carbon nanotubes (CNTs) with poly(3-hexylthiophene-2,5-diyl) (P3HT) having different degrees of regioregularity. Regioregular P3HT gave much higher power factors, showing the need of regioregularity in the polymer for best TE results. TE power factors (PFs) up to 148 μW m−1 K−2 were obtained by optimizing multiple factors, including: (i) P3HT sample type, (ii) relative amount and type of CNT, (iii) sample fabrication solvent, and (iv) composite doping duration. The TE performance improvements in the composites arose from greatly increased electrical conductivity by doping and CNT addition, coupled with limited decreases in Seebeck thermopower. Extensive network formation was seen by scanning electron microscopy (SEM) in composites with higher CNT fraction, which is believed to provide better charge transport pathways to improve PFs. Multiwall CNT composites showed much lower PFs compared to singlewall CNT composites, attributable (at least in part) to poor nanotube dispersion.
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