New Sb₂Te_3-Se Monolayers with High Electron Mobilities and Wide Absorption Range

As a traditional thermoelectric material with high thermoelectric performance at room temperature, antimony telluride (Sb₂Te₃) has been widely used in energy applications like power generation and refrigeration. By employing the "atomic transmutation" method, three new kinds of Sb₂Te₃-based monolayers of α-Sb₂Te₂Se, α-Sb₂TeSe₂, and β-Sb₂TeSe₂ are designed, which are expected to possess a high thermoelectric performance due to the quantum-confinement effects. In this work, by using the ab initio calculations, we systematically study electronic structures, vibration modes, optical, transport, and thermoelectric properties for the three kinds of monolayers and find that they are indirect-band-gap semiconductor materials with chemical and thermodynamic stability up to 700 K (α-Sb₂TeSe₂) or 900 K (α-Sb₂Te₂Se and β-Sb₂TeSe₂). The band gaps are around 1.0 eV with five nearly degenerate peaks in valence bands. The three Sb₂Te_3-Se monolayers possess high electron mobilities larger than 1000 cm²/(V s), and the maximum zT values of α-Sb₂Te₂Se/α-Sb₂TeSe₂/β-Sb₂TeSe₂ are 0.70/0.71/0.65 at 300 K, respectively. For optical properties, the three Sb₂Te_3-Se monolayers possess a wide absorption range from the blue region to the ultraviolet region. Compared with Sb₂Te₃, the three new kinds of monolayers possess a wider range of absorptions, higher mobilities, and thermoelectric performances, which may lead to promising applications in thermoelectric devices and saturable absorbers.