Dynamic carrier transports and low thermal conductivity in n‐type layered InSe thermoelectrics

Abstract

Semiconductor InSe with wide bandgap and layered crystal structure is expected to be a promising thermoelectric material, and its excellent plasticity brings great potential applications in flexible and wearable thermoelectric devices. To advance its thermoelectric performance, this work systematically investigates the carrier and phonon transport properties in n‐type InSe. It is found that InSe compound presents an exceptional dynamic carrier transport property due to the amphoteric indium (In+ and In3+), which contributes to favorable temperature‐dependent increasing carrier concentration. More importantly, with S alloying in InSe, the carrier concentration can be further enhanced from ∼3.2 × 1013 cm–3 in InSe to ∼4.8 × 1015 cm–3 in InSe0.97S0.03 at 300 K, because S (χP ∼ 2.58) with larger Pauling electronegativity than Se (χP ∼ 2.55) can induce more In3+ state to increase carrier concentration in matrix. This boosted dynamic carrier transport property benefits an obviously enhanced power factor. Additionally, InSe compound presents intrinsically low thermal conductivity ∼1.6 W m–1 K–1 at 300 K due to low‐symmetry crystal structure and strong anharmonicity. This work indicates that the special dynamic carrier transport property and intrinsically low thermal conductivity in InSe make it as a worth‐expecting thermoelectric material.

Direct Measurements of Anisotropic Thermal Transport in γ‐InSe Nanolayers via Cross‐Sectional Scanning Thermal Microscopy

“…[ 70,71 ] We note that these thicknesses and lateral tip displacements are larger than the corresponding phonon mean free path λ of γ‐InSe, which is of the order of 3 nm, as reported elsewhere. [ 72 ] The upper bound of the mean free path for γ‐InSe can also be estimated using the kinetic model (λ = 3 k z C v −1 υ s −1 ) where υ s is the speed of sound, C v is the volumetric heat capacity [ 73 ] and k z are the literature reported thermal conductivity values of layered γ‐InSe (≈2 Wm −1 K −1 ). [ 27,41,73 ] This results in a mean free path λ < 5 nm.…”

“…[70,71] We note that these thicknesses and lateral tip displacements are larger than the corresponding phonon mean free path λ of γ-InSe, which is of the order of 3 nm, as reported elsewhere. [72] The upper bound of the mean free path for γ-InSe can also be estimated using the kinetic model…”

Carrier and phonon transport in 2D InSe and its Janus structures

“…Si doping can decrease the average RT κ to a very small value of 1.6 W m −1 K −1 [141]. The κ of InSe 0.95 S 0.05 is ∼0.6 W m −1 K −1 at 723 K [142]. That suggested that there is a large space to modulate the κ of 2D InSe.…”

Pressure-Induced Anisotropic to Isotropic Thermal Transport and Promising Thermoelectric Performance in Layered InSe

“…Layered InSe has gained considerable attention because of its potential applications in flexible thermoelectric devices stemming from exceptional deformability and plasticity. , For its monolayer counterpart, many researchers have demonstrated the excellent thermoelectric performance and investigated the possibility of improving the performance through external stimuli. − For its bulk counterpart, it is well-known that there exist three different polytypes characterized by the arrangement of the layers, which are described as β-, ε-, and γ-polytypes. − The β- and ε-polytypes belong to the hexagonal system, while the γ-polytype has rhombohedral symmetry. Previous studies mainly focused on the optimization of the carrier concentration and mobility of β-InSe, − while the thermoelectric properties of γ-InSe, not to mention the effect of pressure on the electronic and thermal transport properties in γ-InSe, are rarely addressed.…”