Band Degeneracy and Anisotropy Enhances Thermoelectric Performance from SbSiTe to ScSiTe.

The complex interrelationships among thermoelectric parameters mean that design of high-performing materials is difficult. However, band engineering can allow the power factor to be optimized through enhancement of the Seebeck coefficient. Herein, using layered SbSiTe and ScSiTe as model systems, we comprehensively investigate and compare their thermoelectric properties by employing density functional theory combined with semiclassical Boltzmann transport theory. Our simulations reveal that SbSiTe exhibits superior electrical conductivity compared to ScSiTe due to lower scattering rates and more pronounced band dispersion. Remarkably, despite SbSiTe exhibiting a lower lattice thermal conductivity and superior electrical conductivity, ScSiTe is predicted to achieve an extraordinary dimensionless figure of merit () of 3.51 at 1000 K, which significantly surpasses the predicted maximum of 2.76 for SbSiTe at 900 K. We find the origin of this behavior to be a combined increase in band (valley) degeneracy and anisotropy upon switching the conduction band orbital character from Sb p to Sc d, yielding a significantly improved Seebeck coefficient. This work suggests that enhancing band degeneracy and anisotropy (complexity) through compositional variation is an effective strategy for improving the thermoelectric performance of layered materials.