Strong anisotropy of ScXSe (X = Cl, Br, I) monolayers contributes to high thermoelectric performance.

As a novel type of anisotropic two-dimensional material, extensive attention has been paid to the thermoelectric (TE) properties of FeOCl-type monolayers, such as AlXSe (X = Cl, Br, I), ScIS, and IrClO. Recently, theoretical works based on first-principles calculations have been powerful driving forces in field of TE research. In this work, we perform an investigation into the TE properties of ScXSe (X = Cl, Br, I) monolayers based on density functional theory (DFT). A study on the stability, including AIMD simulation and phonon calculation, shows the stable structure of ScClSe, ScBrSe, and ScISe monolayers. Additionally, the electronic and thermal transport properties of ScXSe monolayers are anisotropic along the and directions. Moreover, the combination of excellent Seebeck coefficient and ultralow lattice thermal conductivity contributes to outstanding values, and the values follow the order: ScISe > ScBrSe > ScClSe. At 300 K, we obtained maximum of 0.34, 0.77, and 1.97 for ScClSe, ScBrSe, and ScISe, respectively, by n-type doping in the direction. These results demonstrate that monolayer ScXSe (X = Cl, Br, I) materials are promising thermoelectric materials, ScISe has more desirable properties along the direction, and n-type doping can significantly enhance the values. Our work lays a foundation for exploring the TE transport properties of FeOCl-type monolayers.