Variations of thermoelectric performance by electric fields in bilayer MX2 (M = W, Mo; X = S, Se). Issue 8 (8th February 2017)

• Record Type: Journal Article
• Authors: Wang, Rui-Ning; Dong, Guo-Yi; Wang, Shu-Fang; Fu, Guang-Sheng; Wang, Jiang-Long
• Is Part Of: Physical chemistry chemical physics. Volume 19:Issue 8(2017)
• Page Start: 5797
• Page End: 5805
• Publication Date: 2017-02-08
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c6cp05952j
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : A gate is usually used to controllably tune the carrier concentrations, further modulating the electrical conductivity and Seebeck coefficient to obtain the optimum thermoelectric figure of merit in two-dimensional materials. On the other hand, it is necessary to investigate how an electric field induced by a gate affects the electronic structures, further determining the thermoelectric properties. Abstract : A gate electrode is usually used to controllably tune the carrier concentrations, further modulating the electrical conductivity and the Seebeck coefficient to obtain the optimum thermoelectric figure of merit ( ZT ) in two-dimensional materials. On the other hand, it is necessary to investigate how an electric field induced by a gate voltage affects the electronic structures, further determining the thermoelectric properties. Therefore, by using density functional calculations in combination with Boltzmann theory, the thermoelectric properties of bilayer MX2 (M = W, Mo; X = S, Se) with or without a 1 V nm −1 perpendicular electric field are comparatively investigated. First of all, the variations of the electrical conductivity ( σ ), electron thermal conductivity and Seebeck coefficient ( S ) with the carrier concentration are studied. Due to the trade-off relationship between S and σ, there is an optimum concentration to obtain the maximum ZT, which increases with the temperature due to the enhancement of the Seebeck coefficient. Moreover, N-type bilayers have larger optimum ZT s than P-type bilayers. In addition, the electric field results in the increase of the Seebeck coefficient in low hole-doped MS2 bilayers and high hole-doped MSe2 bilayers, thus leading to similar variations in ZT . The optimum ZT s are reduced from 2.11 × 10 −2, 3.19 × 10 −2, 2.47 × 10 −2, and 2.58 × 10 −2 to 1.57 × 10 −2, 1.51 × 10 −2, 2.08 × 10 −2, and 1.43 × 10 −2 for the hole-doped MoS2, MoSe2, and WSe2 bilayers, respectively. For N-type bilayers, the electric field shows a destructive effect, resulting in the obvious reduction of the Seebeck coefficient in the MSe2 layers and the low electron-doped MS2 bilayers. In electron-doped bilayers, the optimum ZT s will decrease from 3.03 × 10 −2, 6.64 × 10 −2, and 6.69 × 10 −2 to 2.81 × 10 −2, 3.59 × 10 −2, and 4.39 × 10 −2 for the MoS2, MoSe2, and WSe2 bilayers, respectively.