Plastic/Ductile Bulk 2D van der Waals Single‐Crystalline SnSe₂ for Flexible Thermoelectrics

Abstract

The recently discovered ductile/plastic inorganic semiconductors pave a new avenue toward flexible thermoelectrics. However, the power factors of current ductile/plastic inorganic semiconductors are usually low (below 5 μW cm −1 K −2 ) as compared with classic brittle inorganic thermoelectric materials, which greatly limit the electrical output power for flexible thermoelectrics. Here, large plasticity and high power factor in bulk two-dimensional van der Waals (2D vdW) single-crystalline SnSe 2 are reported. SnSe 2 crystals exhibit large plastic strains at room temperature and they can be morphed into various shapes without cracking, which is well captured by the inherent large deformability factor. As a semiconductor, the electrical transport properties of SnSe 2 can be readily tuned in a wide range by doping a tiny amount of halogen elements. A high power factor of 10.8 μW cm −1 K −2 at 375 K along the in-plane direction is achieved in plastic single-crystalline Br-doped SnSe 2 , which is the highest value among the reported flexible inorganic and organic thermoelectric materials. Combining the good plasticity, excellent power factors, as well as low-cost and nontoxic elements, bulk 2D vdW single-crystalline SnSe 2 shows great promise to achieve high power density for flexible thermoelectrics.

Toughening Thermoelectric Materials: From Mechanisms to Applications

“…More importantly, a deformability factor was proposed to select other candidate plastic bulk materials, , where , , and are the cleavage energy, slipping energy, and the in-plane Young’s modulus along the slip direction, respectively, which is in good agreement with early literature [ 40 ]. Based on this rule, an important deformability factor is the existence of bulk 2D vdW single-crystalline SnSe 2 ( Figure 1 e), which endures a large bending strain as high as 15% in a three-point bending test without cracking and retains good integrity on the microscopic scale [ 41 ]. The calculated along (001)<120> is 0.022 eV per atom, lower than InSe along (001)[100] and Ag 2 S along (100)[001], while the along (001) is 0.143 eV per atom, higher than InSe and Ag 2 S. Therefore, is much higher than those of ductile InSe and Ag 2 S, as visualized in Figure 1 f.…”

“…Copyright 2018 American Association for the Advancement of Science). ( e ) The crystal structure of SnSe 2 [ 41 ]. ( f ) The deformability factors (Σ) of ductile semiconductors, metals, and brittle materials (Reprinted from ref [ 41 ] under the terms of a Creative Commons CC BY License.…”

Superflexible Inorganic Ag2Te0.6S0.4 Fiber with High Thermoelectric Performance

“…The recently discovered ductile inorganic semiconductors based on silver sulfide realize the integration of high electrical mobility and mechanical flexibility in one single-phased inorganic material, [26] which opens a new utility in flexible inorganic TE materials. [27][28][29][30] For instance, a unique inorganic material Ag 2 Te 0.6 S 0.4 with both extraordinary plastic deformability and high room temperature TE performance is developed. [31] It can be reshaped into flexible slice without compromising the TE performance.…”

High-Throughput Screening of Deformable Inorganic Layered Semiconductors

“…8 Recently, a few notable inorganic semiconductors, such as Zn 2 S, 9 Ag 2 S, 10 and InSe, 11 were reported to possess excellent deformability at room temperature. Afterward, a series of plastic deformable van der Waals layered materials such as CrCl 3 , 12 SnSe 2 , 13 and SnIP 14 were reported. These discoveries stimulated intensive interest in exploring more deformable inorganic layered semiconductors.…”