Development of carbon nanotube organic thermoelectric materials using cyclodextrin polymer: control of semiconductor characteristics by the solvent effect

The π-type organic thermoelectric conversion modules composed of p-type and n-type materials that convert low-temperature waste heat into electric energy have the potential to significantly increase energy efficiency. However, p-type and n-type materials are difficult to prepare by similar methods since they have opposite carriers. In this study, we achieved γ-cyclodextrin polymer-carbon nanotube (PγCyD-CNT) composite thermoelectric film that can control the carrier by the solvent effect. When the preparation solvent switched from water to N-methylpyrrolidone (NMP), the carriers of the film were converted from holes to electrons, and their power factor values at 345 K were 221.0 and 246.6 μW m−1K−2. Moreover, PγCyD-CNTs film prepared in NMP retained n-type characteristics for half a year under the ambient atmosphere. Interestingly, the residual NMP contained in the film acts as a dopant agent for CNTs, and the chemical interaction of γCyD and NMP in the polymer results in sustained n-doping.