Enhanced Thermoelectric Performance of Conjugated Polymer/CNT Nanocomposites by Modulating the Potential Barrier Difference between Conjugated Polymer and CNT

Small-bundled single-walled carbon nanotube (SSWCNT) nanocomposite films with two different conjugated polymers were facilely prepared by using a micronizing mill. The influence of the difference in the electronic structures and molecular orientations of poly(3-hexylthiophene) (P3HT) and poly(diketopyrrolopyrrole–selenophene) (PDPPSe) on the thermoelectric properties of polymer/SSWCNT nanocomposites was systematically investigated. Planar-shaped PDPPSe with stronger π–π interaction, compared to that in P3HT, naturally forms a dense surface microstructure with SSWCNT by easily wrapping the SSWCNT surface. Furthermore, the inherent crystalline orientation of PDPPSe effectively enhances the electrical conductivity of the SSWCNT nanocomposite film by inducing the alignment of SSWCNT bundles in an in-plane direction. In the electronic structure of the composite, PDPPSe lowers the interfacial energy barrier between the polymer and SSWCNT to induce the carrier-filtering effect, which can facilitate charge transport from the polymer to SSWCNT. The PDPPSe/SSWCNT nanocomposite exhibits a considerably increased electrical conductivity of 537.7 S cm–1 and a higher Seebeck coefficient of 62.5 μV K–1 compared to those of the P3HT/SSWCNT nanocomposite. The optimized power factor of the PDPPSe/SSWCNT nanocomposite is 210 μW m–1 K–2, which is about 10 times higher than that of the P3HT/SSWCNT nanocomposite. The thermoelectric generator fabricated from PDPPSe/SSWCNT displays a high open-circuit voltage (Voc) of 8.5 mV and short-circuit current (Isc) of 162.8 μA, resulting in a maximum output power of 0.35 μW at ΔT = 10 °C.