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Page 2 of 9 Ao et al. Soft Sci 2024;4:3 https://dx.doi.org/10.20517/ss.2023.34

INTRODUCTION
Thermoelectric (TE) technology can achieve direct conversion between thermal energy and electrical
[1-5]
energy, which has significant applications in power generation and refrigeration . With an increasing
demand for micro-electromechanical systems of chip-sensors, wearable electronics, and implantable
electronic devices, the TE flexible thin films (f-TFs) have attracted extensive interest due to their high
adaptability to various conditions with high TE performance [6-10] . The TE performance of f-TFs can be
2
[11]
accessed via power factor (S σ) , where σ and S represent the electric conductivity and Seebeck coefficient,
respectively. Herein, σ is defined as σ = n eμ, where n , e, and μ represent carrier concentration, elementary
h
h
charge, and carrier mobility, respectively [12,13] . The S can be evaluated by Mott formula [14,15] . The increase of S
*
can be achieved by the decreased n and increased effective mass (m ). However, it is a significant challenge
h
to simultaneously increase the S and σ due to their coupled relationship. Typically, f-TFs are composed of
organic f-TFs and inorganic f-TFs [16,17] . For typical organic f-TFs, such as 3-hexylthiophene-2, 5-diyl
(FeCl -doped P3HT, S σ = ~0.2 μW·cm ·K at 340 K) , carbon nanotubes/polyaniline (CNTs/PANI,
[18]
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2
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3
[19]
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S σ = ~4.07 μW·cm ·K at room temperature) , and poly (3,4-ethyl enedioxythiophene) polystyrene
-1
sulfonate (PEDOT/PSS, S σ = ~3.34 μW·cm ·K at room temperature) , a room temperature S σ is lower
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2
-2
[20]
than 5.0 μW·cm ·K . Inorganic f-TFs, such as Ag Se (S σ = ~18.6 μW·cm ·K at room temperature) ,
[21]
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-1
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-2
2
2
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2
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[22]
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-2
[23]
SnSe (S σ = ~3.5 μW·cm ·K at 300 K) , Cu Se (S σ = ~11.12 μW·cm ·K at 549 K) , n-type Bi Te
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(S σ = ~14.65 μW·cm ·K at room temperature) , p-type Sb Te (S σ = ~21.0 μW·cm ·K at room
[24]
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2
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temperature) , have been attracted great attention from the TE research community. It is evident that
[25]
inorganic f-TFs approaches exhibited higher S σ than that of the organic f-TFs, depicting good potential for
2
commercial applications.
Among inorganic TE f-TFs, p-type Sb Te f-TFs with a narrow bandgap of ~0.3 eV possess good TE
3
2
[26]
performance at near room temperature . So far, numerous methods have been employed to synthesize
[29]
p-type Sb Te f-TFs [27-32] , such as thermal evaporation , magnetron sputtering , solution printing , and
[31]
[30]
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thermal diffusion . Vieira et al. realized a high σ of ~320 S·cm and S σ of ~12.0 μW·cm ·K at 298 K for
[32]
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-1
2
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Sb Te f-TFs prepared by thermal evaporation . Shang et al. successfully prepared (00l)-preferential
[29]
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orientation p-type Sb Te f-TFs by magnetron sputtering methods and approached the σ of ~740 S·cm and
-1
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2
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2
S σ of ~12.4 μW·cm ·K at 300 K. Sb Te f-TFs prepared by screen-printing technology can approach σ of
-2
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3
~250 S·cm and S σ of ~14.3 μW·cm ·K at room temperature [30,31] . It is concluded that the σ of Sb Te f-TFs
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prepared by most of the preparation methods is lower than 1,000 S·cm due to poor crystal growth.
Consequently, the carrier transport properties were suppressed, and the corresponding TE performance of
Sb Te f-TFs is also limited.
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In the present work, we employed a thermal diffusion method to prepare p-type Sb Te f-TFs on a flexible
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2
polyimide (PI) substrate. The Sb and Te precursor films were deposited by thermal evaporation, as shown in
Figure 1A. Pure Sb and Te f-TFs were obtained separately. The schematic diagram of the thermal diffusion
process and the optical image of as-prepared Sb Te f-TFs are shown in Figure 1B. The copper mold consists
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2
of a convex mold on the top and a concave mold placed below. Cu molds at both the top and bottom can
enhance heat conduction and improve the uniformity of heat distribution during the thermal diffusion
process. The Sb Te f-TFs were synthesized by thermal diffusion methods using Te and Sb pure precursor
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3
films. The schematic diagram of the reaction process of Sb and Te during the thermal diffusion process is
shown in Figure 1C. Through tuning the thermal diffusion temperature (T ), the Sb Te f-TFs with
diff
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2
standard stoichiometric ratios were obtained. Moreover, the moderate Seebeck coefficient of > 95 μV·K was
-1
achieved at room temperature. Simultaneously, the μ and σ increased with increasing T due to the
diff
weakened carrier scattering. Correspondingly, the highest value of S σ of 16.0 μW·cm ·K at T = 623 K has
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-1
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diff
been achieved. Besides, our prepared Sb Te f-TFs approach good bending resistance.
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