Br-Doped n-Type SnSe₂: Single-Crystal Growth and Thermoelectric Properties

Abstract

In this work, pure, large Br-doped SnSe2 single crystals were successfully synthesized using the temperature gradient technique. Br acts as a donor, resulting in electron concentrations up to ∼6.83 × 1019 cm–3 at room temperature. All samples exhibited metal-like electrical resistivities and Seebeck coefficient behaviors over a temperature range of 300–673 K. Br doping greatly improved the power factor, especially along the in-plane direction. We observed anisotropy in the electrical conductivity, Seebeck coefficient, and, most notably, thermal conductivity. An ultralow thermal conductivity was achieved along the out-of-plane direction, leading to a maximum ZTc of 0.54 at 673 K in the Br-doped sample, which is twice as large as that of the in-plane direction, ZTa = 0.25.

Optimization of the Thermoelectric Properties of SnSe2 Using First-Principles Calculations

“…Although the PFT value is higher in the in-plane direction, it could not compensate the κ normala κ normalc ratio. So, the overall ZT value is higher in the cross-plane direction, and it reaches unity at 950 K. Experimentally, the maximum ZT value of 0.56 for single-crystal SnSe 2 is reported at 673 K along the cross-plane direction . Our optimized ZT value is 0.545 at 673 K, which is close to the experimental value (0.56).…”

“…Finally, to report ZT of SnSe 2 , lattice thermal conductivity is calculated using Callaway’s model and as described in the methodology part. It was reported experimentally that total thermal conductivity is dominated by phonon transport (∼95% of total) and so we limited our calculation to the lattice part of thermal conductivity . Calculated thermal conductivity in comparison with experimentally measured results is shown in Figure a.…”

“…For instance, Sun's model 28 predicted a larger ZT in the in-plane direction, whereas experimental results suggest that ZT is higher along the cross-plane direction for single-crystal samples. 25,30 The discrepancies between theoretical and experimental values also originated from the incorrect modeling of lattice thermal conductivity. As shown in ref 26, Cahill's model 31 was used which is only applicable to disorder systems and not to SnSe 2 .…”

Plastic/Ductile Bulk 2D van der Waals Single‐Crystalline SnSe2 for Flexible Thermoelectrics

“…Due to the weak chemical bonding between the adjacent layers, the bulk SnSe 2 crystal is easy to cleave, forming smooth surfaces (Figure 2b ). [ 34 , 35 ] As shown in Figure 2c , only the (00 l ) ( l = 1, 2, 3, …) diffraction peaks can be detected on the cleaved surface, confirming the high quality of the crystals. Energy dispersive spectroscopy (EDS) mapping indicates that Sn and Se elements are homogeneously distributed inside the matrix (Figure 2d ).…”

Recent advances of substitutionally doped tin dichalcogenides

“…61 Pham et al achieved a high Br doping concentration of 7.5% by the CVT method using SnBr 2 as the dopant. 62 The as-prepared single crystal had a zTc ( zT along out-of-plane direction) of 0.54 at 673 K, which was seven times higher than that of pristine SnSe 2 . Kim et al achieved a zT value of 0.62 at 750 K with a 1% Br doping concentration [Fig.…”