Lattice Strain Leads to High Thermoelectric Performance in Polycrystalline SnSe

Abstract

Polycrystalline SnSe materials with ZT values comparable to those of SnSe crystals are greatly desired due to facile processing, machinability, and scale-up application. Here manipulating interatomic force by harnessing lattice strains was proposed for achieving significantly reduced lattice thermal conductivity in polycrystalline SnSe. Large static lattice strain created by lattice dislocations and stacking faults causes an effective shortening in phonon relaxation time, resulting in ultralow lattice thermal conductivity. A combination of band convergence and resonance levels induced by Ga incorporation contribute to a sharp increase of Seebeck coefficient and power factor. These lead to a high thermoelectric performance ZT ∼ 2.2, which is a record high ZT reported so far for solution-processed SnSe polycrystals. Besides the high peak ZT, a high average ZT of 0.72 and outstanding thermoelectric conversion efficiency of 12.4% were achieved by adopting nontoxic element doping, highlighting great potential for power generation application at intermediate temperatures. Engineering lattice strain to achieve ultralow lattice thermal conductivity with the aid of band convergence and resonance levels provides a great opportunity for designing prospective thermoelectrics.

The Importance of Surface Adsorbates in Solution‐Processed Thermoelectric Materials: The Case of SnSe

“…To illustrate this, we plotted the Seebeck coefficient as a function of charge carrier concentration (Pisarenko plot) at 300 K and compared it with reported experimental data and first‐principles calculations using a multiple band model [ 84 ] in Figure 5E. The plot reveals that not only our Na–SnSe sample but also many other solution‐processed SnSe (half‐filled green symbols) [ 22,27,29,31,42,43,85 ] have Seebeck coefficients exceeding the expected value, a tendency not observed in Na‐doped solid‐state synthesized SnSe (black open symbols, [ 47,53,77,78,86 ] including single crystals [ 87,88 ] ).…”

“…Mater. 2021, 33, 2106858 E) Pisarenko plot at 300 K. Green dots are references from solutionprocessed materials [22,27,29,31,42,43,85] and black dots from solid-state synthetic methods, [47,53,77,78,86] including single crystals. [87,88] The dashed line was calculated using a multiple band model.…”

“…[16][17][18] Alternatively, surfactants can be exchanged with volatile compounds [19] or even inorganic species [20] that can further tune material properties. [12,18,21] Conversely, the presence of surface adsorbates is usually neglected in the case of the so-called surfactant-free methods, [4,[22][23][24][25][26][27][28][29][30][31][32][33][34] the most widely used to produce thermoelectric powders in solution. The vast majority of reports dealing with surfactant-free synthesis do not perform any surface treatments since the particles are considered "naked".…”

“…A) Electrical conductivity, σ; B) Seebeck coefficient, S; C) power factor, PF; D) thermal conductivity, κ; Na-SnSe, Me 4 N-SnSe, and Me 4 N-SnSe + Na samples measured in the direction parallel to the pressing axis. E) Pisarenko plot at 300 K. Green dots are references from solutionprocessed materials[22,27,29,31,42,43,85] and black dots from solid-state synthetic methods,[47,53,77,78,86] including single crystals [87,88]. The dashed line was calculated using a multiple band model [84].…”

Biaxial Tensile Strain-Induced Enhancement of Thermoelectric Efficiency of α-Phase Se2Te and SeTe2 Monolayers

“…The corresponding maximum p-type doping ZT reaches up to 0.64 (1.67), which is 1.6 (2.5) times higher than that of unstrained structures. Such a high value of ZT of strained structures is larger than those of most reported 2D materials, such as α-Te [ 57 ], SiTe 2 [ 58 ], SnTe 2 [ 58 ], and XSe (X = Ge, Sn, and Pb) [ 50 ], and even larger than typically single and polycrystalline crystal SnSe [ 59 , 60 ], indicating tensile strain is an effective category to enhance the thermoelectric effect.…”