Role of interlayer coupling for the power factor of ${\mathrm{CuSbS}}_2$ and ${\mathrm{CuSbSe}}_2$

The electronic and transport properties of bulk and monolayer ${\mathrm{CuSbS}}_2$ and ${\mathrm{CuSbSe}}_2$ are determined by using density functional theory and semiclassical Boltzmann transport theory, in order to investigate the role of interlayer coupling for the thermoelectric properties. The calculated band gaps of the bulk compounds are in agreement with experiments and significantly higher than those of the monolayers, which thus show lower Seebeck coefficients. Since also the electrical conductivity is lower, the monolayers are characterized by lower power factors. Therefore, interlayer coupling is found to be essential for the excellent thermoelectric response of ${\mathrm{CuSbS}}_2$ and ${\mathrm{CuSbSe}}_2$, even though it is weak.

Figure 1

Crystal structure of bulk and monolayer $\mathrm{CuSb}{X}_2$ ($X=\text{S}$ and Se).

Figure 2

Band structure and density of states of bulk and monolayer ${\mathrm{CuSbS}}_2$ and ${\mathrm{CuSbSe}}_2$.

Figure 3

Seebeck coefficient, electrical conductivity, electronic contribution to the thermal conductivity, and power factor as a function of the hole ($p$) and electron ($n$) densities for bulk ${\mathrm{CuSbS}}_2$ (solid line) and ${\mathrm{CuSbSe}}_2$ (dashed line).

Figure 4

Seebeck coefficient, electrical conductivity, electronic contribution to the thermal conductivity, and power factor as a function of the hole ($p$) and electron ($n$) densities for monolayer ${\mathrm{CuSbS}}_2$ (solid line) and ${\mathrm{CuSbSe}}_2$ (dashed line).

Figure 5

Power factor of bulk and monolayer ${\mathrm{CuSbS}}_2$ and ${\mathrm{CuSbSe}}_2$ at the hole concentration that maximizes the value at 300 K in each case.

Figure 6

Total energy convergence for increasing density of the $k$ mesh in the case of ${\mathrm{CuSbS}}_2$.

Figure 7

Recalculation of Fig. 2 with finer $k$ meshes of $8\times 13\times 3$ (bulk) and $15\times 9\times 1$ (monolayer), demonstrating convergence of the results.