Monodispersed semiconducting SWNTs significantly enhanced the thermoelectric performance of regioregular poly(3-dodecylthiophene) films

The improved thermoelectric (TE) properties of conducting polymers are generally achieved through the use of single-walled carbon nanotubes (SWNTs) as additives. However, their aggregation and aggregation-induced over-loading of SWNTs generally result in high thermal and low electrical conductivity. Herein, sc-SWNTs were selectively captured by regioregular poly(3-dodecylthiophene)(rr-P3DDT) in a toluene solution containing a semiconducting and metallic carbon nanotubes mixture (mix-SWNTs) to achieve rr-P3DDT films with monodispersed semiconducting SWNTs (rr-P3DDT/sc-SWNT). The single sc-SWNTs were tightly wrapped by a rrP3DDT layer with a thickness of several nanometers, which was orderly aligned at the micrometer scale. The large number of rr-P3DDT/sc-SWNT nanointerfaces present in composite films contributed to increasing carrier mobility through 7C-7C conjugation while reducing the thermal conductivity via phonon scattering. Thus, the rrP3DDT/sc-SWNT films had significantly higher electrical conductivity and lower thermal than the rr-P3DDT/ mix-SWNT composite films. Both the electrical conductivity and Seebeck coefficient of the rr-P3DDT/sc-SWNT composite films were much greater than the calculated values using the parallel connected mixture model. The maximum ZT value of the rr-P3DDT/sc-SWNT composite film was 0.1, approximately 18 times greater compared to the rr-P3DDT/mix-SWNT films and among the highest for the polymer/carbon nanotube composites. This work provides a convenient but efficient method to maximize the TE properties of conducting polymers.