Structural modulation and resonant level enable high thermoelectric performance of GeTe in the mid-to-low temperature range

GeTe has recently attracted wide attention as a promising mid-temperature thermoelectric candidate, but the poor performance severely limits its practical application. Herein, we demonstrate the significantly improved thermoelectric properties of Sb-InSe codoped GeTe by structural modulation and introducing a resonant level. It is revealed that both the phase transition at lower temperature driven by Sb doping and resonant level induced by InSe doping can increase the density of states effective mass, leading to an improved Seebeck coefficient and power factor over a wide temperature range. Additionally, the Sb-InSe codoping introduces various defects in the GeTe matrix and enhances the phonon scattering to obviously decrease the lattice thermal conductivity in the whole temperature range. With these synergistic effects, the (Ge0.91Sb0.09Te)(0.99)(InSe)(0.01) sample achieves a peak zT(max) of 2.1 at 773 K and a high zT(avg) of 1.61 between 400 and 773 K.