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Single-walled carbon nanotubes (SWCNTs) are desirable flexible thermoelectric materials in applications of large-scale low-grade thermal energy. However, weak Seebeck coefficients of SWCNTs around room temperature limit their development as a flexible power generator. In this work, we significantly improve the Seebeck coefficients of SWCNT-based composites by integrating the discotic liquid-crystal 2,3,6,7,10,11-hexakis(hexyloxy) triphenylene (HAT6) through the energy-filtering effect. The Seebeck coefficients of SWCNT/HAT6 composite films are about more than twice that of the pristine SWCNT films, and a maximum power factor of 408.23 ± 48.96 μW m −1 K −2 is achieved at room temperature, which is one of the highest values among organic small-moleculebased thermoelectric composites reported so far. The flexible power generator based on p-type SWCNT/HAT6 films is first assembled. An outstanding power density of 0.64 μW cm −2 with a thermoelectric voltage of 17.64 mV at a temperature gradient of 56 K is achieved. This study demonstrates that SWCNT/ discotic liquid-crystal composites show great promise in thermoelectric (TE) materials and open a new avenue for the development of TE devices.

It is crucial for thermoelectric (TE) devices to obtain both p-type and n-type materials and control charge carrier density. However, n-type thermoelectric materials are quite deficient and have lower thermoelectric properties. We report one oxygen-rich polymer named polyethylene glycol (PEG) for converting p-type single-walled carbon nanotubes (SWCNTs) to air-stable n-type thermoelectric materials. When pristine SWCNTs were doped with 2 mg·mL–1 PEG in an ethanol solution, the optimal Seebeck coefficient of PEG/SWCNT composites reached −50.8 μV·K–1. The result of ultraviolet photoelectron spectroscopy demonstrated that the lone pair of oxygen atoms in the PEG chain has electron transferability to SWCNTs. According to the hard and soft acid and base theory, sodium hydroxide (NaOH) was further introduced to improve air stability and thermoelectric performance of doped SWCNTs. As a result, PEG/NaOH/SWCNT composites achieved the highest power factor of 173.8 μW·m–1·K–2 at 300 K. Meanwhile, their final changes in electrical conductivity and the Seebeck coefficient are less than 8% in the investigation of air stability over two months. Inspired by this finding, we fabricated the TE generator composed of the pristine p-type SWCNTs and n-type PEG/NaOH/SWCNT composites. The maximum output power of this robust TE device reached 5.3 μW at a temperature gradient of 76 K, which is superior to many reported TE devices. Moreover, the experimental procedure is attractive as a sustainable process for materials preparation. Our study has indicated that the oxygen-rich polymer-functionalized SWCNTs have huge potential for developing air-stable n-type carbon-based thermoelectric materials.

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Introducing two-dimensional (2D) conjugated structures to polymers is a feasible way for the design of functionalized polymers due to their good planarity, high electron/hole mobility, thermal stabilities, and so forth. However, the current development of thermoelectric polymers is mainly restricted to the limited modification of the one-dimensional conjugated polymers. Herein, a novel donor−acceptor based 2D conjugated polymer, P(BDTTT-DPP), was designed and synthesized for the enhancement of thermoelectric properties. Compared to the onedimensional conjugated polymer P(BDT-DPP), P(BDTTT-DPP) showed a higher doping level when doped with the p-type FeCl 3 dopant. After doping with 20 mg/mL FeCl 3 for 15 min, the optimal power factor of P(BDTTT-DPP) was obtained to be 6.50 μW m −1 K −2 at room temperature, which is 26 times higher than that of P(BDT-DPP). The studies of film morphology and packing structure analysis further indicated that the π−π stacking (010) distance of P(BDTTT-DPP) was maintained after the doping process, and the longer lamellar stacking distance allowed the FeCl 3 dopants to efficiently incorporate between the lamellar domains compared to that of P(BDT-DPP), which is favorable to the crystallinity and electron transferability. The results of our work provide valuable insights into the development of donor−acceptor based 2D conjugated polymer for high-performance organic thermoelectric materials.