Significant improvement in the thermoelectric properties of zwitterionic polysquaraine composite films

In this study, the polysquaraine SQI0.1, a zwitterionic π-conjugated polymer, was adopted as the matrix for the preparation of flexible and freestanding films; the low band gap of this semiconducting polymer made it a natural choice for use as a thermoelectric (TE) polymer. To enhance their TE applications, both single-walled carbon nanotubes (SWNTs) and mesoporous carbon (i.e., CMK-3) were integrated into the SQI0.1-based films and the effects of doping with iodine were also investigated. Using scanning electron microscopy, the variations in morphology of these SQI0.1-based films were examined. Raman spectroscopy was used to study the π–π interactions between iodine and the carbon materials (i.e., SWNT, CMK-3); X-ray diffraction and Raman spectroscopy to investigate the intercalation of the doped iodine in the composite films; and X-ray photoelectron spectroscopy to determine the valence state of the doped iodine. The TE properties of these materials were characterized in terms of the electrical conductivity (σ), thermal conductivity (κ), and Seebeck coefficient (S). The TE properties of the iodine-doped composite film prepared from SWNTs, CMK-3, and SQI0.1 included a notable value of ZT (Figure of Merit) of 4.563 × 10−3, which was 143% of that of the corresponding iodine-doped SQI0.1 film.