Anomalous thermal transport of vertically stacked PtSe2 thin films with interface formation

Abstract

Two-dimensional (2D) transition metal dichalcogenide (TMDC) materials are indispensable candidates for thermoelectric (TE) device applications. However, thermal transport at low temperatures, as an important TE device application, has not been fully realized, especially in large-area 2D TMDC films. Here, we report temperature-dependent in-plane Seebeck coefficients, along with electrical and thermal conductivities, of both 3 nm-thick PtSe₂ films and stacked 2D/2D semiconducting PtSe₂/PtSe₂ (3 nm/3 nm) homostructures at temperatures ranging from 40 to 300 K using a homemade Seebeck coefficient measurement module and a heat diffusion imaging method, respectively. In the single 2D PtSe₂ (3 nm) film, simultaneous decreases in the in-plane Seebeck coefficient and electrical conductivity were observed with decreasing temperature, indicating the presence of both semiconductor and metallic properties. At 300 K, the in-plane Seebeck coefficient of the single 2D PtSe₂ film is ∼65.1 μV K⁻¹, whereas those of the 2-, 3-, and 4-stacked PtSe₂/PtSe₂ homostructures are ∼69.1, ∼79.0 and ∼72.0 μV K⁻¹, respectively due to interface formation between the PtSe₂ layer. The in-plane thermal conductivity of the single PtSe₂ film is ∼28.3 W m⁻¹ K at 300 K and reaches maximum values of ∼98.5 and ∼12.1 W m⁻¹ K at 97 and 42 K, respectively. Our findings demonstrate the feasibility of utilizing 2D semiconducting PtSe₂ layers with interface formation between the 2D layers as TE energy-saving and energy-generating devices, as they exhibit the TE properties required by an ideal TE material.