Promoting thermoelectric performance of two-dimensional benzodithiophene-based conjugated polymer/single-walled carbon nanotube composites by polar side chain engineering

Single-walled carbon nanotube (SWCNT) based polymer composites have been developed as potent thermoelectric (TE) materials. Unfortunately, the effect of polymers' structure on the composite's TE performance remains unclear. In addition, the research on the backbone of polymers in the SWCNT based composites is limited to the one-dimensional conjugated ones, and the distinct influence of linear and macrocyclic polar side chains on TE performances remains unexplored. Herein, two kinds of benzodithiophene(BDT)-based two-dimensional (2D) conjugated polymers decorated with linear tetraethylene glycol (P(BDTP)) and macrocyclic crown ether (P(BDTC)), respectively, were designed and synthesized, and their effect on the TE performance of SWCNTs was systematically studied. The results indicated 2D BDT-based backbone exhibited strong binding ability to SWCNTs due to the expanded 2D conjugated structure. P(BDTC) displayed stronger π-π intermolecular interactions with SWCNTs than P(BDTP) due to the annular crown ester on the side chain, which were verified by fluorescence, Raman, X-ray photoelectron and scanning electron microscopy results. At the mass ratios of 1:2, P(BDTC)/SWCNT composites gained an optimized power factor of 137.7 ± 7.9 μW m−1 K−2, achieving 181% enhancement than P(BDTP)/SWCNT composites (75.1 ± 1.6 μW m−1 K−2). Consequently, P(BDTC)/SWCNT composites-based generator exhibited the maximum actual output power of 327.9 nW at the temperature difference of around 70 K, which is 1.31 times higher than that of P(BDTP)/SWCNT-based generator (247.5 nW). Hence, incorporating macrocyclic polar side groups in conjugated polymers provides a promising structural modification strategy for organic counterparts in polymer/SWCNT composites.