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Page 20 of 26 Wang et al. Soft Sci 2023;3:34 https://dx.doi.org/10.20517/ss.2023.25

Table 5. Room-temperature TE properties of 2D materials
S σ PF
Materials Preparation method 2 ZT Ref.
(μV/K) (S/cm) (μW/mK )
MoS Lithium intercalation, 93.5 17.5 13 0.01 [113]
2
WS 2 Lithium intercalation 45 30 4.05 ~ [114]
WS /SWCNT Hydrothermal 43.2 318 61.7 ~ [115]
2
Mo TiC T Wet-chemical process -47.3 1,380 309 (803K) ~ [22]
2 x
2
Ti C T /SWCNTs/Ti C T Lithium intercalation, layer-by-layer stacking -32.2 750.9 77.9 ~ [116]
3 2 x 3 2 x
Bi Te Se /Ti C T Physical mixing, hot pressing -148 830 1,818 1.2 [117]
0.3
2.7
2
3 2 x
TE: Thermoelectric; ZT: thermoelectric figure of merit; PF: PEDOT:PSS-functionalized; SWCNTs: single-walled carbon nanotubes.

Figure 15. (A) Schematic illustrations for exfoliation of SnSe particles into nanosheets; (B) Fabrication of flexible
SWCNT/SnSe/PEDOT:PSS nanocomposite films; (C) Digital photos for fabrication of the free-standing, flexible
[118] ©
SWCNT/SnSe/PEDOT:PSS composite films. Reproduced with permission from Ref . Copyright 2020. John Wiley and Sons.
PEDOT:PSS: Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid); SWCNT: single-walled carbon nanotube.

Seebeck coefficients and combining a conducting polymer matrix with low thermal conductivity to prepare
ternary composites shall be an effective strategy to achieve excellent TE properties. In such cases, the
interfacial contact and interaction between components will directly affect the film formation and
properties. The direct vacuum filtration method has been proven to be a good choice. By vacuum filtration,
Liu et al. prepared flexible SWCNT/SnSe/PEDOT:PSS nanocomposite films on a nylon membrane
[118]
2
[Figure 15A-C] . At 380 K, an optimized power factor of 109.9 μW/mK was obtained. The films showed
excellent flexibility as their electrical conductivity decreased by 1% after 1000 bending cycles. A flexible TEG
is assembled on a polyimide substrate of 8-unit free-standing composite film strips. It generated an open-
circuit voltage of 20.6 mV and a maximum output power of 1.16 μW at a temperature gradient of 74.4 K.
Other materials with enhanced TE performance have been prepared using similar methods, such as
SWCNT/PEDOT:PSS/Te (104 μW/mK 2[119] ), MWCNT/PEDOT:PSS/Se (73.94 μW/mK 2[120] ), and MWCNTs/
PEDOT:PSS/SnSe (166.5 μW/mK 2[121] ).

As mentioned above, Ag Se is a particularly excellent inorganic TE material. To further improve the TE
2
performance of Ag Se, Lu et al. have conducted a series of studies on Ag Se-based ternary composite
2
2
materials by vacuum filtration. By adjusting the molar ratio of Cu :Ag :Se in the precursor, they prepared
2-
+
2+