Flexible thermoelectric generators (FTEGs) offer a promising solution for powering wearable electronics, while their practical applications are mainly obstructed by the moderate properties of flexible thermoelectric (TE) materials. Here, flexible Ag₂Se nanowire (NW)/methyl cellulose (MC) composite films were developed via facile screen-printing technology combined with cold pressing and annealing treatment, and a highest power factor of 1,641.58 μW m⁻¹ K⁻² at 360 K was achieved. The reasons for the high TE performance of the Ag₂Se NW/MC composite films were because, after the annealing treatment, the Ag₂Se NWs were sintered to form conductive network structures, the crystallinity of Ag₂Se was markedly enhanced, and the content of insulating phase MC in the composite film was decreased. The Ag₂Se NW/MC composite film held appreciable flexibility, as its room-temperature power factor (1,312.08 μW m⁻¹ K⁻²) can retain ~93% after bending for 1,000 cycles at a radius of 4 mm. Furthermore, the assembled FTEG consisting of 4 strips can generate a maximal power density of 3.51 W m⁻² at a temperature difference of 14.1 K. Our results open an effective and large-scale strategy for fabricating high-performance flexible TE materials and energy-harvesting devices.

Flexible thermoelectric generators (f-TEGs) are of importance for self-powered, portable, and wearable electronics. The materials’ thermoelectric (TE) performance is one of the factors that affect the conversion efficiency of f-TEGs. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a kind of conducting polymers has low thermal conductivity and good processability in solution; however, its TE properties are still much lower than those of the inorganic TE materials, which limits its wide applications in f-TEGs. Two-dimensional (2D) inorganic nanosheets (NSs) exfoliated from their corresponding powders are promising filler materials for enhancing the TE properties of PEDOT:PSS. This paper provides a brief review on the research progress of flexible 2D inorganic NS/PEDOT:PSS composite films fabricated by vacuum filtration, drop casting, and spin coating. The challenges, perspectives, and outlooks of flexible 2D inorganic NS/PEDOT:PSS composite films are further discussed.

Polyaniline (PANI) was prepared by in-situ polymerization and compounded on the two-dimensional network structural multi-walled carbon nanotube film (CNTF). Compared with the CNT/PANI composites fabricated by using CNT powders or dispersions, the compact and continuous network structure of CNTF/PANI is beneficial to both the thermoelectric and mechanical properties of the composites. The resultant CNTF/PANI composites with PANI polymerization time of 5 h obtain an electrical conductivity of 1338.4 S/cm and Seebeck coefficient of 63.3 μV/K at 360 K, which are 168.7% and 5.7% higher than those of the CNTF (498.1 S/cm and 59.9 μV/K at 360 K). Consequently, a maximum power factor of 536.8 μW·m⁻¹·K⁻² at 360 K is acquired, which is about 2 times higher than that of CNTF (181.7 μW·m⁻¹·K⁻² at 360 K). The electrical conductivity of the composites could maintain 93.3% after being bent for 500 times, indicating the excellent flexibility. The tensile strength, Young's Modulus and toughness of CNTF/PANI composites (232.3 MPa, 3.6 GPa and 20.1 MJ/m³, respectively) are 3.5, 2.6 and 2.1 times of those of the CNTF. The flexible, free-standing, lightweight and high-strength CNTF/PANI composites reveal the excellent thermoelectric performance, which are promising in the applications in wearable thermoelectric devices.

Carbon nanotube film (CNTF) with two-dimensional CNT network structure is adopted to prepare CNTF/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thermoelectric composites, which overcomes the disadvantages of low content, easy aggregation, and random orientation of CNTs when dispersed in polymer. A vacuum-assisted filtration method was proposed, which can uniformly and sufficiently penetrate the polymer into CNTF along thickness direction for fabrication of CNTF/PEDOT:PSS composites. A highest electrical conductivity of 806.2 S/cm at 300 K was achieved for the composites with 60 wt% PEDOT:PSS loading, which was 51.0% higher than that of the original CNTF (534.1 S/cm). A maximum power factor of 339.6 μW·m⁻¹·K⁻² at 320 K was achieved with a corresponding Seebeck coefficient of 67.7 μV/K. This study provides a universal method for fabrication of other kinds of CNTF/conductive polymer thermoelectric composites.

In this work, poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) coated silver telluride (PCAg₂Te) nanorods were prepared by a wet-chemical method using the PEDOT:PSS coated tellurium (PCTe) nanorods as the templates. Flexible PCAg₂Te nanocomposite film on polyethersulfone (PES) substrate was prepared through vacuum filtration followed by mechanical pressing process. An optimal PCAg₂Te nanocomposite film showed a maximum power factor of 143.3 μW/mK² at room temperature and 221.7 μW/mK² at 373 K. The electrical conductivity of the PCAg₂Te composite film decreased by ∼ 3.3% after bending for 1000 times around a rod with a radius of 5 mm. An eight-leg thermoelectric generator assembled with the optimal PCAg₂Te nanocomposite film generated a maximum output power and output density of 209.4 nW and 141.5 μW/cm² at a temperature gradient of 30.3 K. This work provides a facile method to prepare thermoelectric materials for flexible thermoelectric generators.