Improved In-plane Seebeck Coefficient in PtTe₂/MoS₂ Hetero-junction Structure

Two-dimensional (2D) transition metal dichalcogenides (TMDc) is rapidly emerging as a material for thermoelectric (TE) devices. The energy conversion efficiency of the thermoelectric materials is figure of merit, ZT=PF×T/κ (where PF=S²×σ, PF is power factor, T is absolute temperature, κ is thermal conductivity, S is Seebeck coefficient, σ is electrical conductivity). In order to achieve a high ZT, it is important to obtain a high PF, and a low κ. Except for T and κ, it is important to improve PF=S²×σ. Unfortunately, Seebeck coefficient and electrical conductivity are through trade-off relations. In this report, we develop a PtTe₂/MoS₂ hetero-junction structure to break this trade-off relationship. The 2D PtTe₂ and MoS₂ films are synthesized by using low-pressure chemical vapor deposition (LP-CVD) method. The 2D PtTe₂ film exhibits a semi-metallic property with low resistance (≤ 2 kΩ), whereas the MoS₂ is considered as an insulator with high resistance (≥ 10 MΩ). We prepared five sets of samples, including PtTe₂ (5-nm), PtTe₂ (5-nm)/MoS₂ (7-nm), PtTe₂ (5-nm)/MoS₂ (7-nm)/MoS₂ (7-nm), PtTe₂ (5-nm)/MoS₂ (21-nm), and PtTe₂(5-nm)/MoS₂ (21-nm)/MoS₂ (21-nm). As a result, we observe that the in-plane Seebeck coefficient for PtTe₂ (5-nm)/MoS₂ (7-nm)/MoS₂ (7-nm) hetero-junction structure is -19 μV/K at 300K. It indicates an increase of ~200% compared to that of the PtTe₂ (5-nm) thin film. Also, the electrical conductivity (5.3 kS×cm) is improved by ~170%. Consequently, the power factor (190 μW/K²m) is improved by ~720%. These findings represent that the 2D TMDc hetero-junction structures have good advantages in improving the power factor in future TE applications.