Exploring different doping mechanisms in thermoelectric polymer/carbon nanotube composites

[Display omitted] •Comparison of the thermoelectric properties of different kinds of carbon, nanotubes.•Investigation of undoped single-walled, multi-walled, as well as nitrogen-doped, carbon nanotubes.•Investigation of the effect of the nitrogen-doping method on thermoelectric, performance.•Preparation of carbon nanotube composites with polythiophenes and, polyethylenimine.•UV irradiation allows to tune the doping in polymer/carbon nanotube, composites. This work compares various methods to prepare polymer/carbon nanotube (CNT) composites for thermoelectric applications, focusing on the different doping mechanisms. We first look at the general trends observed in the Seebeck coefficient and power factor for a large number of composites as a function of electrical conductivity. Then we discuss two methods of nitrogen doping the carbon nanotubes in these composites, namely either during synthesis, or afterwards by ammonolysis. Finally, we discuss doping of the carbon nanotubes through charge transfer from the polymer counterpart, including photo-induced switching of the majority carrier type. As a general remark, we note that processability is negatively influenced by some doping procedures. Best results were achieved for unfunctionalized single-walled carbon nanotubes with a high content of semiconducting CNT species.