SWCNT network evolution of PEDOT:PSS/SWCNT composites for thermoelectric application

Although conjugated polymer/carbon nanotube (CNT) thermoelectric (TE) composites have witnessed explosive achievements in recent years, the in-depth mechanism of CNT network evolution and its influence on composite TE performance are still unclear. Herein, we systematically investigate the evolution of single-walled CNT (SWCNT) network structure with a wide SWCNT content range for poly (3,4-ethyienedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS)/SWCNT composites based on TE properties and atomic force microscopic (AFM) observations. The whole curves of TE performance can be divided into three regions with the increase of SWCNT loading. In Region I (< 20 wt% SWCNT), a percolation-like phenomenon is observed with an S-shape change of electrical conductivity and constant Seebeck coefficient, possibly due to the occurrence of SWCNT aggregates besides primary particles. Subsequently, because of energy-filtering effect, in Region II (SWCNT content between 20 wt% and 97.5 wt%), the electrical conductivity decreases, while the Seebeck coefficient gradually increases with increased SWCNT loading. With further increase of SWCNT content (Region III), the TE performances are almost independent of SWCNT content. In addition, the temperature dependence of TE performance and the stability of TE performance against mechanical bending cycles are studied. Finally, a prototype TE device based on PEDOT:PSS/SWCNT composite film is assembled, showing an open-circuit voltage and an output power of 6.6 mV and 1200 nW at a temperature difference of 60 K, respectively. The results are helpful to elucidate the mechanism of structure-property relations for conjugated polymer TE composites, and will benefit their practical applications.