Achieving high Figure of Merit in p-type polycrystalline Sn0.98Se via self-doping and anisotropy-strengthening

Thin Film Tin Selenide (SnSe) Thermoelectric Generators Exhibiting Ultralow Thermal Conductivity

“…[43] This is of interest to the thermoelectric community as it reveals that the thermal conductivity of SnSe can be reduced further than is observed in single-crystal SnSe. [13] Due to the subdued power factor, the resultant peak ZT (0.055) seen in Figure 3c is lower than has been observed for bulk polycrystalline SnSe in the literature, [16][17][18][19][20][21][22][23][24] however is the highest reported ZT for a thin film of SnSe above 70 K. [25,31] We also note the simplicity of fabrication and shift in peak ZT to a lower temperature compared to bulk examples. The high surface area of these films also opens the possibility for molecular adsorption as a gas sensor, [44] which could be self-powered.…”

“…[13] While in single-crystal SnSe, the Seebeck coefficient is seen to drop from ≈550 to ≈350 µV K −1 between 600 and 800 K, [13] for thermally evaporated thin films, the Seebeck coefficient is >600 µV K −1 at room temperature, but drops to ≈140 µV K −1 by 600 K with the drop starting at 460 K. This drop is more pronounced and at lower temperatures compared to single-crystal SnSe. Electrical conductivity (Figure 3a) is seen to be lower than other polycrystalline SnSe examples in the literature at room temperature ( Figure S6, Supporting Information), [16][17][18][19][20][21][22][23][24] but shows a sharp increase above 450 K to reach similar levels. This leads to a lower power factor (Figure 3c) compared to other examples of polycrystalline SnSe.…”

“…This leads to a lower power factor (Figure 3c) compared to other examples of polycrystalline SnSe. [16][17][18][19][20][21][22][23][24] Interestingly, an unprecedentedly low in-plane thermally conductivity for SnSe is observed throughout the temperature profile (Figure 3b,d), which is at its lowermost between 375 and 450 K at 0.08 W m −1 K −1 . This is over a factor of 4 lower than the low-thermal conductivity a-axis of the single crystal at comparable temperatures, and a factor of 2.75 lower when comparing the lowest thermal conductivity values measured.…”

“…[16][17][18][19][20][21][22][23][24] Sassi et al synthesized polycrystalline SnSe in quartz tubes and then densified by spark plasma sintering (SPS) and showed a peak ZT value of 0.5 at 823 K. [16] Li et al achieved a ZT of 0.58 at 773 K in textured SnSe polycrystals fabricated by the solvothermal synthesis (SS) followed by SPS. [21] Shi et al used the same technique but self-doped (SD) with Se to achieve a higher ZT of 1.36 ± 0.12 at 823 K. [17] Wei et al achieved a ZT of 0.8 at 800 K in polycrystalline SnSe with Na doping by using a combination of melting (M) and SPS. [18] Li et al achieved a ZT of 0.54 at 790 K by melting annealing (MA) and SPS.…”

“…[13] This thermal conductivity is also a factor of 2.80 and 1.50 lower than any bulk polycrystalline and thin film SnSe examples, respectively, when comparing with their lowest thermal conductivity values measured. [16][17][18][19][20][21][22][23][24][25] The thermal conductivity of a material is intrinsically comprised of the sum of two components, the electronic element from the charge carriers (κ e ) and the lattice element from the phonons (κ l ). Figure 3b shows that while a negligible amount of the deceased thermal conductivity can be attributed to a reduction in the electronic component (κ e ) due to the lower electrical conductivity (κ e = L·T·σ, assuming L = 1.5 × 10 −8 V 2 K −2 ), [13] the majority of the reduction in thermal conductivity is a result of a significant decrease in the lattice component (κ l ).…”