The role of branched alkylthio side chain on dispersion and thermoelectric properties of regioregular polythiophene/carbon nanotubes nanocomposites

Abstract

Herein, poly(3-alkylthiophene)s (P3ATs) and poly[(3-alkylthio)thiophene]s (P3ATTs) are respectively synthesized using poly(thiophene)s with linear/branched alkyl groups and branched alkylthio moieties with short/long side chain lengths for dispersing single-walled carbon nanotubes (SWCNTs), and the resulting composites are solution-processed for use as p-type thin film thermoelectric devices. With an additional sulfur atom on the side chain, a well-dispersed P3ATTs/SWCNTs nanocomposite is obtained by polymer-wrapping at the SWCNTs surfaces driven by S − π and π − π interactions between the alkylthio side chain substituents and π-conjugated backbones of the P3ATTs and SWCNTs, thereby contributing to greatly improved thermoelectric performance relative to the P3ATs/SWCNTs nanocomposite without the added sulfur. The poly[3-(2-hexyldecylthio)thiophene] (P3HDTT) nanocomposite with the longest alkylthio side chain exhibits the strongest interaction with the SWCNTs, yielding the highest power factor (PF) of 307.7 μW m−1 K−2. The ability of this spray-coated nanocomposite film to generate power is demonstrated with a prototype flexible thermoelectric generator (TEG) that produces 888.1 μW m−2. Thus, the introduction of debundled SWCNTs networks wrapped by P3ATTs with alkylthio side chains suggests a feasible strategy for the design of high-performance thermoelectric materials and opens up new opportunities for capturing waste heat in wearable electronics.