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. 2023 Jan 5;16(2):509.
doi: 10.3390/ma16020509.

Enhanced Room-Temperature Thermoelectric Performance of 2D-SnSe Alloys via Electric-Current-Assisted Sintering

Kesavan Manibalan  1 , Meng-Yuan Ho  1 , You-Cheng Du  1 , Hung-Wei Chen  1 , Hsin-Jay Wu  1
Affiliations

Enhanced Room-Temperature Thermoelectric Performance of 2D-SnSe Alloys via Electric-Current-Assisted Sintering

Kesavan Manibalan et al. Materials (Basel). .

Abstract

Single-crystalline tin-selenide (SnSe) has emerged as a high-performance and eco-friendly alternative to the lead-chalcogens often used in mid-temperature thermoelectric (TE) generators. At high temperature >800 K, the phase transition from Pnma to Cmcm causes a significant rise in the TE figure-of-merit (zT) curve. Conversely, the SnSe TE requires a booster at low temperatures, which allows broader applicability from a device perspective. Herein, a synergy of Cu alloy and Ag-coating is realized through a sequential multi-step synthesis, designed to combine different metal deposition effects. Single-crystalline (Cu2Se)x(SnSe)1−x alloys grown by the Bridgman method were then coated with a thin Ag layer by radio frequency (RF) sputtering, and the interlayer epitaxial film was observed via electric-current assisted sintering (ECAS). Consequently, the thin Ag-coating improves the electrical conductivity (σ) and reduces the thermal conductivity (κ) for (Cu2Se)0.005(SnSe)0.995+Ag alloy, increasing the zT curve at close to room temperature (373 K). The incorporation of multistep addition by ECAS enables tuning of the overall solubility of the alloy, which opens a new avenue to optimize TE performance in anisotropic 2D materials.

Keywords: 2D materials; SnSe single crystal; multistep deposition; radio frequency sputtering; thermoelectrics.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Temperature-dependent zT profiles for (Cu2Se)x(SnSe)1−x (x = 0.005, 0.01 and 0.02) and Ag-coating. The (Cu2Se)0.005(SnSe)0.995 + Ag alloy is denoted as a solid curve, and reported SnSe single-crystal [4] and polycrystal [13] are added for comparison. Inset: Pictographic of TE properties measurement along the in-plane direction (bc plane). (b) Left to right: Crystalline image for κ measurement (left, disk-shaped pellet), PF measurement (middle), cleavage plane from the as-grown bulk SnSe (right). (c) Plate-shaped SnSe alloys are sliced up to measure transport properties. (d) SnSe alloys were placed on a ZEM thin-film stage commercial apparatus for S and σ measurement.
Figure 2
Figure 2
Temperature-dependent (a) Seebeck coefficient, S, (b) electrical conductivity, σ, (c) power factor, S2σ, (d) thermal conductivity, κ of (Cu2Se)x(SnSe)1−x+Ag (x = 0.005, 0.01, and 0.02) alloys.
Figure 3
Figure 3
The electrical conductivity measured from both sides of the (Cu2Se)0.005(SnSe)0.995+Ag alloy (top and back/bottom sides).
Figure 4
Figure 4
XPS analysis of (Cu2Se)0.005(SnSe)0.995 + Ag alloy. (a) Full surface survey spectrum, (b) depth profile, (c) high-resolution scan.
Figure 5
Figure 5
TEM analysis of (Cu2Se)0.005(SnSe)0.995+Ag alloy: (a) A cross-sectional BF image, (b) IFFT image of magnified Ag layer region (c,d) SAED pattern, (e) IIFT image of selected area lattice spacing’s, (f–j) Elemental mapping taken by EDX-STEM.
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