Engineering Electronic Structure and Lattice Dynamics to Achieve Enhanced Thermoelectric Performance of Mn-Sb Co-Doped GeTe

GeTe, as a p-type semiconductor, has been intensively studied in recent years as a promising lead-free mid-temperature-range thermoelectric (TE) material. Herein, we report an improved energy conversion efficiency (eta) using a two-step TE properties optimization in Mn-Sb co-doped GeTe by engineering electronic structure and lattice dynamics. Mn-Sb co-doping enhances the TE properties of GeTe, as evidenced from both experiments and first-principles-based theoretical calculations. The density functional theory (DFT) calculations indicate that Mn-Sb co-doping improves the band convergence and optimizes the Fermi level position. This in turn helps in enhancing the Seebeck coefficient (alpha). As a result of the optimized Seebeck coefficient and electrical conductivity (sigma), an enhanced power factor (alpha(2)sigma) is obtained for the Mn-Sb co-doped system. Moreover, a significant reduction in the phonon (lattice) thermal conductivity (kappa(ph )similar to 0.753 W/mK) at 748 K is observed for Ge0.87Mn0.05Sb0.08Te, attributed to the point-defect scattering and reduced phonon group velocity. The synergistic improvement in alpha and reduction in kappa(ph) result in a maximum figure-of-merit (zT) of 1.67 at 773 K, with an average zT (zT(av)) of similar to 0.9 for Ge0.87Mn0.05Sb0.08Te over a temperature range of 300-773 K, leading to an eta of similar to 12.7%.