Highly mobile carrier-driven Seebeck coefficient enhancement

Band convergence has been utilized as an effective strategy to enhance the Seebeck coefficient, typically by improving the energy dependence of carrier density near the Fermi level. In contrast, the energy dependence of carrier mobility, which can also enhance the Seebeck coefficient, has attracted less attention. Here, we show that the Seebeck coefficient can be improved when the additional converging band contributes highly mobile carriers, even if they have minimal impact on carrier density. The high-mobility carriers enhance the net diffusion flux, promoting carrier accumulation and amplifying the Seebeck voltage. This mobility-driven enhancement exhibits a hump-like feature in the Pisarenko plot, which becomes flatter and shifts toward lower carrier concentrations as the bands approach. The transport properties of p-type rhombohedral GeTe, as a potential case, were experimentally examined. This work deepens the understanding of band convergence-induced Seebeck coefficient enhancement in thermoelectric materials.