Improved Thermoelectric Performance of Monolayer HfS₂ by Strain Engineering

Abstract

Strain engineering can effectively improve the energy band degeneracy of two-dimensional transition metal dichalcogenides so that they exhibit good thermoelectric properties under strain. In this work, we have studied the phonon, electronic, thermal, and thermoelectric properties of 1T-phase monolayer HfS2 with biaxial strain based on first-principles calculations combined with Boltzmann equations. At 0% strain, the results show that the lattice thermal conductivity of monolayer HfS2 is 5.01 W m–1 K–1 and the electronic thermal conductivities of n-type and p-type doped monolayer HfS2 are 2.94 and 0.39 W m–1 K–1, respectively, when the doping concentration is around 5 × 1012 cm–2. The power factors of the n-type and p-type doped monolayer HfS2 are different, 29.4 and 1.6 mW mK–2, respectively. Finally, the maximum ZT value of the n-type monolayer HfS2 is 1.09, which is higher than 0.09 of the p-type monolayer HfS2. Under biaxial strain, for n-type HfS2, the lattice thermal conductivity, the electronic thermal conductivity, and the power factor are 1.55 W m–1 K–1, 1.44 W m–1 K–1, and 22.9 mW mK–2 at 6% strain, respectively. Based on the above factor, the ZT value reaches its maximum of 2.29 at 6% strain. For p-type HfS2, the lattice thermal conductivity and the electronic thermal conductivity are 1.12 and 1.53 W m–1 K–1 at 7% strain, respectively. Moreover, the power factor is greatly improved to 29.5 mW mK–2. Finally, the maximum ZT value of the p-type monolayer HfS2 is 3.35 at 7% strain. It is obvious that strain can greatly improve the thermoelectric performance of monolayer HfS2, especially for p-type HfS2. We hope that the research results can provide data references for future experimental exploration.

Tensile Strain Induced Enhancement in the Thermoelectric Performance of monolayer MoS$_{2}$

“…2. The peak value of the relaxation time coupled thermoelectric PF reaches 36.5 × 10 10 Wm −1 K −2 s −1 at T = 900 K, which is comparable to the best-known thermoelectric materials [34]. In order to calculate the thermoelectric efficiency (ZT), the variation in the lattice thermal conductivity (κ L ) of single-layer MoS 2 with temperature has also been investigated and presented in Fig.…”

“…A low value of κ L is essential to achieve a high value of ZT. The lattice thermal conductivity decreases sharply with increasing temperature and becomes 7.5 Wm −1 K −1 at 900/, K. A decreasing trend has also been observed in other 2D TMDCs such as WS 2 , WSe 2 [47] and HfS 2 [34]. Finally, the variation of the thermoelectric efficiency (ZT) with chemical potential and temperature is explored (Fig.…”

“…As a result of the increased phonon scattering and reduced group velocity, the lattice thermal conductivity decreases with strain application. In MoS 2 , as well as other 2D-TMDCs [34,48], the ZA mode is seen to be the dominant heat conduction carrier. Therefore, the frequency gap between the ZA and the optical modes dictates the intensity of the phonon scattering.…”

“…Strain-engineering, on the other hand, can be a potential alternative to tune the electronic and thermoelectric properties, owing to its simple technique and reversible phenomena [31,32]. The thermoelectric performance of monolayer ZrS 2 and HfS 2 is improved under the action of mechanical strain [33,34]. For monolayer, few-layer and bulk MoS 2 also, the application of strain has been proved to be an efficient way to tune and improve the thermoelectric performance [14].…”

Enhancement in the Thermoelectric Performance of SnS Monolayer by Strain Engineering

“…Strain can be easily induced experimentally through lattice mismatch between the nanosheet and the substrate or by mechanically bending/distorting the nanostructure . Recently, strain-induced electronic band degeneracy was seen to improve the thermoelectric performance of bulk SnS and SnSe and monolayer HfS 2 , InSe, and ZrS 2 . A recent work reported 5.3 times higher ZT for a SnS bilayer upon the application of 2% tensile strain along the zigzag direction of the bilayer.…”