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

Abstract

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 (V oc) of 8.5 mV and short-circuit current (I sc) of 162.8 μA, resulting in a maximum output power of 0.35 μW at ΔT = 10 °C.

Lignin Doped Carbon Nanotube Yarns for Improved Thermoelectric Efficiency

“…Furthermore, as shown in Figure 1e, it is likely that when the CNTY interacts with lignin molecules via the aforementioned π–π interactions, the equilibrium energy band at the CNTY/lignin interface is driven toward a lower energy barrier state that ultimately facilitates the mobility of high‐energy carriers whilst filtering out low‐energy carriers via a carrier filtering effect. [ 13 ] Thereby, leading to enhanced charge transport from lignin to CNTY. The electrical conductivity is a result of the balance between reduced carrier concentration and enhanced carrier mobility.…”

Polymer‐Based Low‐Temperature Thermoelectric Composites

“…Kang and co‐workers [ 76 ] report a more conventional processes by mixing CNTs with polymer, by using small‐bundled carbon nanotubes (SSWCNTs), that is, the connected stacks of nanotubes. The filler was incorporated via micronizing mill into two different polymers: P3HT and poly(diketopyrrolopyrelle‐selenophene) (PDPPSe) within dichlorobenzene as a solution.…”

“…a) Filtering mechanism alongside tunneling via enhanced concentration of SWCNTs, Reproduced with permission. [ 76 ] Copyright 2019, American Chemical Society. b) Scheme of ordering of the polymer structure, Reproduced with permission.…”

Multi‐Fidelity High‐Throughput Optimization of Electrical Conductivity in P3HT‐CNT Composites

“…[ 27–30 ] However, the electrical conductivity (σ) of P3HT/CNT composites requires significant improvement in order to make this class of nanocomposites viable for practical applications. Various strategies are proposed to increase the electrical conductivity of P3HT/CNT composites including molecular doping of P3HT, use of different CNT types, [ 31 ] process optimization, tuning the energy barrier between the polymer and CNT [ 32 ] and improvement of the crystalline structure or morphology of P3HT and CNT. [ 33–35 ] Most of these approaches are concentrated on enhancing inter‐chain charge transport by improving the degree of crystallinity or nanoscale architecture of P3HT chains induced by CNTs.…”