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Thickness-controlled electronic structure and thermoelectric performance of ultrathin SnS2 nanosheets.

ABSTRACT: The thermoelectric conversion efficiency of a material relies on a dimensionless parameter (ZT?=?S 2 ?T/?). It is a great challenge in enhancing the ZT value basically due to that the related transport factors of most of the bulk materials are inter-conditioned to each other, making it very difficult to simultaneously optimize these parameters. In this report, the negative correlation between power factor and thermal conductivity of nano-scaled SnS2 multilayers is predicted by high-level first-principle computations combined with Boltzmann transport theory. By diminishing the thickness of SnS2 nanosheet to about 3?L, the S and ? along a direction simultaneously increase whereas ? decreases, achieving a high ZT value of 1.87 at 800?K. The microscopic mechanisms for this unusual negative correlation in nano-scaled two dimensional (2D) material are elucidated and attributed to the quantum confinement effect. The results may open a way to explore the high ZT thermoelectric nano-devices for the practical thermoelectric applications.

SUBMITTER: Li J

PROVIDER: S-EPMC5567102 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature

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Thickness-controlled electronic structure and thermoelectric performance of ultrathin SnS2 nanosheets.

Li Jun J Shen Jinni J Ma Zuju Z Wu Kechen K

Scientific reports 20170821 1

The thermoelectric conversion efficiency of a material relies on a dimensionless parameter (ZT = S <sup>2</sup> σT/κ). It is a great challenge in enhancing the ZT value basically due to that the related transport factors of most of the bulk materials are inter-conditioned to each other, making it very difficult to simultaneously optimize these parameters. In this report, the negative correlation between power factor and thermal conductivity of nano-scaled SnS<sub>2</sub> multilayers is predicted ...[more]

PMID: 28827756

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Project description:Transition metal dichalcogenides (TMDs) receive significant attention due to their outstanding electronic and optical properties. In this study, we investigate the electronic, optical, and thermoelectric properties of single and few layer [Formula: see text] in detail utilizing first-principles methods based on the density functional theory (DFT). Within the scope of both PBE and HSE06 including spin orbit coupling (SOC), the simulations predict the electronic band gap values to decrease as the number of layers increases. Moreover, spin-polarized DFT calculations combined with the semi-classical Boltzmann transport theory are applied to estimate the anisotropic thermoelectric power factor (Seebeck coefficient, S) for [Formula: see text] in both the monolayer and multilayer limit, and S is obtained below the optimal value for practical applications. The optical absorbance of [Formula: see text] monolayer is obtained to be slightly less than the values reported in literature for 2H TMD monolayers of [Formula: see text], [Formula: see text], and [Formula: see text]. Furthermore, we simulate the impact of defects, such as vacancy, antisite and substitution defects, on the electronic, optical and thermoelectric properties of monolayer [Formula: see text]. Particularly, the Te-[Formula: see text] substitution defect in parallel orientation yields negative formation energy, indicating that the relevant defect may form spontaneously under relevant experimental conditions. We reveal that the electronic band structure of [Formula: see text] monolayer is significantly influenced by the presence of the considered defects. According to the calculated band gap values, a lowering of the conduction band minimum gives rise to metallic characteristics to the structure for the single Te(1) vacancy, a diagonal Te line defect, and the Te(1)-[Formula: see text] substitution, while the other investigated defects cause an opening of a small positive band gap at the Fermi level. Consequently, the real ([Formula: see text]) and imaginary ([Formula: see text]) parts of the dielectric constant at low frequencies are very sensitive to the applied defects, whereas we find that the absorbance (A) at optical frequencies is less significantly affected. We also predict that certain point defects can enhance the otherwise moderate value of S in pristine [Formula: see text] to values relevant for thermoelectric applications. The described [Formula: see text] monolayers, as functionalized with the considered defects, offer the possibility to be applied in optical, electronic, and thermoelectric devices.

Dataset Information

Thickness-controlled electronic structure and thermoelectric performance of ultrathin SnS2 nanosheets.

Publications

Thickness-controlled electronic structure and thermoelectric performance of ultrathin SnS2 nanosheets.

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