Tailoring the electronic and thermoelectric properties of the SnSe monolayer via vacancy defects: insights from density functional theory

Abstract

Vacancy-defect engineering has been recognized as an effective strategy for tailoring the electronic and thermoelectric properties of 2D materials. In this study, we employed density functional theory (DFT) to investigate the impact of vacancies on the electronic and thermoelectric properties of the SnSe monolayer. Four models were considered: perfect SnSe monolayer, Sn_0.94Se monolayer (Sn vacancy), SnSe_0.94 monolayer (Se vacancy), and Sn_0.94Se_0.94 monolayer (Sn–Se vacancies). Structural analysis revealed that the Sn vacancy induces the most significant lattice rearrangement, followed by the Se and Sn–Se vacancies. From an electronic perspective, the SnSe monolayer is a semiconductor with an indirect bandgap of 0.908 eV. Introducing the Sn vacancy transforms it into a p-type conductor with high electrical conductivity, while the Se vacancy reduces the bandgap to 0.508 eV but preserves its semiconducting nature. In contrast, Sn–Se vacancies enlarge the bandgap to 1.039 eV. A strong correlation between the electronic and thermoelectric transport properties was also observed. Systems with larger bandgaps exhibit higher Seebeck coefficients, with the Sn_0.94Se_0.94 monolayer achieving the maximum value of 1.510 × 10⁻³ V K⁻¹. Thermoelectric performance optimization shows that the Sn_0.94Se monolayer is the most promising candidate at low temperatures (300–400 K), reaching a peak power factor of 2.226 × 10⁻³ W m⁻¹ K⁻². Moreover, vacancy introduction significantly reduces the electronic and thermal conductivity, further reinforcing the Sn_0.94Se monolayer as an optimal candidate for thermoelectric applications in the low-temperature range.