Strain Tunable Thermoelectric Material: Janus ZrSSe Monolayer.

Thermoelectric (TE) performance of the Janus ZrSSe monolayer under biaxial strain is systematically explored by the first-principles approach and Boltzmann transport theory. Our results show that the Janus ZrSSe monolayer has excellent chemical, dynamical, thermal, and mechanical stabilities, which provide a reliable platform for strain tuning. The electronic structure and TE transport parameters of the Janus ZrSSe monolayer can be obviously tuned by biaxial strain. Under 2% tensile strain, the optimal power factor PF of the n-type-doped Janus ZrSSe monolayer reaches 46.36 m W m-1 K-2 at 300 K. This value is higher than that of the most classical TE materials. Under 6% tensile strain, the maximum ZT values for the p-type- and n-type-doped Janus ZrSSe monolayers are 4.41 and 4.88, respectively, which are about 3.83 and 1.49 times the results of no strain, respectively. Such high TE performance can be attributed to high band degeneracy and short phonon relaxation time under strain, causing simultaneous increase of the Seebeck coefficient and suppression of the phonon thermal transport. Present work demonstrates that the Janus ZrSSe monolayer is a promising candidate as a strain-tunable TE material and stimulates further experimental synthesis.

Boosting thermoelectric performance of HfSe2 monolayer by selectivity chemical adsorption.

In this work, a strategy to boosting thermoelectric (TE) performance of 2D materials is explored. We find that, appropriate chemical adsorption of atoms can effectively increase the TE performance of HfSe2 monolayer. Our results show that the adsorption of Ni atom on HfSe2 monolayer (Ni-HfSe2) can improve the optimal power factor PF and ZT at 300 K, increased by more than ∼67% and ∼340%, respectively. The PF and ZT of Ni-HfSe2 at 300 K can reach 85.06 mW m-1 K-2 and 3.09, respectively. The detailed study reveal that the adsorption of Ni atom can induce additional conductional channels of electrons, enhance the coupling of acoustic-optical phonons and the phonon anharmonicity, resulting in an obvious increment of electrical conductivity (increased by more than ∼89%) in n-type doped system and an ultralow phonon thermal conductivity (1.17 W/mK at 300 K). The high electrical conductivity and ultralow phonon thermal conductivity results in the significant increments of PF and ZT. Our study also shows that, Ni-HfSe2 is a thermal, dynamic and mechanical stable structure, which can be employed in TE application. Our research indicates that selectivity chemical adsorption is a promising way to increase TE performance of 2D materials.