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The thermoelectric properties of telluride nanorods coated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (Te-PEDOT:PSS) were enhanced by the addition of a small amount of a nanocarbon material such as graphene nanoparticles (GNPs) or small bundled single-walled carbon nanotubes (SSWNTs). In order to apply the nanocarbon composite material to the printing process, soluble Te-PEDOT:PSS was mixed with a small amount of nanocarbon without degrading the thermoelectric performances. The thermoelectric properties of the Te-PEDOT:PSS nanocomposites were greatly improved, especially when a rather small amount of SSWNTs was added to Te-PEDOT:PSS owing to the structural and electrical properties of the SSNWTs. The power factor of Te-PEDOT:PSS films mixed with 0.3 wt% of SSWNTs was optimized to be 206 μW m−1 K−2, with a Seebeck coefficient of 118 μV K−1 and electrical conductivity of 139 S cm−1. The fabricated thermoelectric generator (TEG) with SSWNT-mixed Te-PEDOT:PSS by spray printing showed output power of 126 nW, which is 18 times higher than that of GNP-mixed Te-PEDOT:PSS. Using the SSWNT-mixed Te-PEDOT:PSS solution, a lightweight, flexible, and highly efficient TEG was fabricated by an all-printing process, and it could generate a small amount of electricity with heat from the human body.

The development of n-type polymers and composites to pair with their p-type counterparts in current flexible thermoelectric (TE) generators is crucial to reach the full potential of these devices. However, this development has lagged behind because of difficulties associated with n-type doping of organic semiconductors. Our study focused on the doping characteristics of directly spun carbon nanotube (CNT) webs using various n-type dopants in combination with thermal desorption of oxygen from the CNT web surface for more effective n-type doping. Annealing of the CNT web followed by treatment with 2 mg mL−1 benzyl viologen (BV) resulted in a maximum power factor of 3103 μW m−1 K−2, which was superior to that of a BV-treated pristine CNT web without thermal annealing (1901 μW m−1 K−2). This value is the highest among organic TE materials and similar to that of the most promising inorganic material, Bi2Te3 at room temperature. In addition to the effect of BV dopants on the electrical properties, the thermal diffusion property of the BV-doped CNT web was analyzed using the finite element method. The dopant coating on the CNT bundle efficiently suppressed the phonon transfer along the CNT web direction, which led to a reduction of the thermal conductivity of the CNT web. As a counterpart for the n-type CNT web, p-type TE materials with a thermal power of 2252 μW m−1 K−2 were also prepared using molecular dopants of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane. Finally, a p–n junction-type TE module with an unprecedented power density of 1.18 mW cm−2 was fabricated based on the development of these competitive n-type TE materials.

This study investigates a coating method for doping a single-walled carbon nanotube (SWCNT)/poly(3-hexylthiophene) (P3HT) hybrid film. In the hybrid film, P3HT chains were very highly doped by simple spin-coating of a FeCl3/nitromethane solution. Hybrid films doped by spin-coating exhibited power factors of 267 ± 38 µW m−1 K−2, which is an improvement over that of hybrid films doped by conventional immersion, 103 ± 24 µW m−1 K−2. The excellent thermoelectric performance is originated from the dramatically increased electrical conductivity by the sufficient doping of P3HT in the hybrid films.

This study demonstrates the fabrication of high-performance thermoelectric carbon nanotube/poly(3-hexylthiophene) (CNT/P3HT) nanocomposite films and flexible CNT/P3HT organic thermoelectric generators (OTEGs) by spray-printing. The spray-printed few-walled CNT/P3HT nanocomposite films exhibited excellent thermoelectric properties. The Seebeck coefficient, electrical conductivity, and power factor of the nanocomposite films were 97 ± 11 μV K−1, 345 ± 88 S cm−1, and 325 ± 101 μW m−1 K−2, respectively, at room temperature. We fabricated flexible OTEGs solely from p-type CNT/P3HT nanocomposite patterns spray-printed on a polyimide substrate, and confirmed their electric power generation capabilities.