The Cross-Linking Effect on the Thermoelectric Properties of Conjugated Polymer/Carbon Nanotube Composite Films

Composite insulating organic material with conducting inorganic nanomaterial is a promising way to compensate the electrical conductivity, which is a prerequisite for the practical realization of the organic thermoelectrics. It is demonstrated that organic-inorganic interfacial interactions play critical rules for composites' thermoelectric performance. Here, an alternative interfacial engineering approach is proposed; that is, post-blending cross-linking of conjugated polymers (CPs). CPs substituted by exo-olefin side chains that can form covalent cross-linking via ruthenium-catalyzed olefin metathesis are newly designed and synthesized. Pre-cross-link CP/single-walled carbon nanotube (SWCNT) composites exhibit relatively high power factor that reach up to 70.3 mu W m(-1) K-2. It is found that the cross-linking process, using second generation Grubbs reagent, is detrimental to the thermoelectric performance. Cross-linked composites exhibit much lower power factor (0.77-19.7 mu W m(-1) K-2) mainly due to the low electric conductivity of the samples, while there is no significant change in Seebeck coefficient. It may be because the formation of tightly cross-linked network hinders the transport of carriers in CP/SWCNT, resulting in a significant decrease in the electric conductivity. These structure-property relationship studies provide useful guidelines for designing organic thermoelectric materials with performance improvement and applied green processing.