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Wang et al. Soft Sci 2023;3:34 https://dx.doi.org/10.20517/ss.2023.25 Page 17 of 26

Table 3. Room-temperature TE properties of the Ag Se-based flexible film
2
S σ PF
Materials Preparation method 2 ZT Ref.
(μV/K) (S/cm) (μW/mK )
Ag Se Wet-chemical process, hot pressing -140 497 987 0.6 [92]
2
Ag 1.98 Ga 0.02 Se Wet-chemical process, hot pressing -115 ~880 1,162 ~ [94]
Ag S Se Wet-chemical process, hot pressing -106 849 954.7 ~ [95]
2 1-y y
Ag Se Optimized wet chemical method, hot pressing -143 919 1,880 0.8 [96]
2
PVP coated Ag Se In-situ synthesis, hot pressing -143 929 1,910 1.1 [97]
2
Ag Se A one-pot synthesis method, hot pressing -150 908 2,043 ~ [98]
2
Ag/Ag Se Wet-chemical process, hot pressing -68.5 3,958 1,860.6 ~ [99]
2
Ag/Ag Se Microwave-assisted synthesis method -89.6 3,030 2,431 > 0.55 [100]
2
Ag/Ag Se Wet-chemical process, hot pressing -91.5 2,720.1 2,277.3 0.71 [101]
2
BC/Ag Se Wet-chemical process, blending + hot pressing -60 810 291 ~ [102]
2
PVDF/Ag Se Wet-chemical process, blending -95.9 205.52 189.02 ~ [103]
2
Ag Se Chemical template method -82.33 385.42 261.26 ~ [104]
2
BC: Bacterial cellulose; TE: thermoelectric; ZT: thermoelectric figure of merit; PF: PEDOT:PSS-functionalized; PVP: poly(vinylpyrrolidone); PVDF:
polyvinylidene fluoride.

Figure 12. (A-D) Cross-sectional microstructure characterization of the PVP/Ag Se composite films: (A) a typical cross-sectional TEM
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image indicating the existence of pores surrounded by several grains (grains A-G); (B) the enlarged image of the red square marked in
(A) showing a coherent interface and a PVP layer; (C) the enlarged image of the green square marked in (A) containing four Ag Se
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grains coated with PVP; (D) an HRTEM image of the white square marked in (C) containing a coherent interface, with a corresponding
FFT image given in the inset; Temperature dependent (E) Seebeck coefficient, electrical conductivity and power factor; and (F) carrier
mobility and concentration of the composite film; (G-I) Flexibility test of the composite film: (G) The electrical conductivity and Seebeck
coefficient of the composite film as a function of bending times with a bending radius of 4 mm; (H) the degradation of power factor of
the composite films as a function of bending times with a bending radius of 4 mm; (I) the stress-strain curve of the composite films (P0:
[97] ©
hot-pressed Ag Se films; P1: hot-pressed PVP/Ag Se films). Reproduced with permission from Ref . Copyright 2021. Elsevier. FFT:
2 2
Fast Fourier transform; HRTEM: high-resolution transmission electron microscopy; PVP: poly(vinylpyrrolidone); TEM: transmission
electron microscopes.
solid solution-substituted Ag S films prepared by vacuum filtration method are also reported, and the TE
[112]
2
properties are listed in Table 4. All the films show good flexibility, enabling the fabrication of flexible TEGs
and paving the way for the commercial application of self-powered wearable electronics.