Improved Thermoelectric Performance of Monolayer HfS(2) by Strain Engineering.

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 HfS(2) 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 HfS(2) is 5.01 W m(-1) K(-1) and the electronic thermal conductivities of n-type and p-type doped monolayer HfS(2) are 2.94 and 0.39 W m(-1) K(-1), respectively, when the doping concentration is around 5 × 10(12) cm(-2). The power factors of the n-type and p-type doped monolayer HfS(2) are different, 29.4 and 1.6 mW mK(-2), respectively. Finally, the maximum ZT value of the n-type monolayer HfS(2) is 1.09, which is higher than 0.09 of the p-type monolayer HfS(2). Under biaxial strain, for n-type HfS(2), 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 HfS(2), 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 HfS(2) is 3.35 at 7% strain. It is obvious that strain can greatly improve the thermoelectric performance of monolayer HfS(2), especially for p-type HfS(2). We hope that the research results can provide data references for future experimental exploration.