Boosting the Thermoelectric Properties of Ge_0.94Sb_0.06Te via Trojan Doping for High Output Power

Abstract

GeTe stands as a promising lead-free medium-temperature thermoelectric material that has garnered considerable attention in recent years. Suppressing carrier concentration by aliovalent doping in GeTe-based thermoelectrics is the most common optimization strategy due to the intrinsically high Ge vacancy concentration. However, it inevitably results in a significant deterioration of carrier mobility, which limits further improvement of the zT value. Thus, an effective Trojan doping strategy via CuScTe 2 alloying is utilized to optimize carrier concentration without intensifying charge carrier scattering by increasing the solubility of Sc in the GeTe system. Because of the high doping efficiency of the Trojan doping strategy, optimized hole concentration and high mobility are obtained. Furthermore, CuScTe 2 alloying leads to band convergence in GeTe, increasing the effective mass m* in (Ge 0.84 Sb 0.06 Te 0.9 )(CuScTe 2 ) 0.05 and thus significantly improving the Seebeck coefficient throughout the measured temperature range. Meanwhile, the achievement of the ultralow lattice thermal conductivity (κ L ∼ 0.34 W m −1 K −1 ) at 623 K is attributed to dense point defects with mass/strain-field fluctuations. Ultimately, the (Ge 0.84 Sb 0.06 Te 0.9 )(CuScTe 2 ) 0.05 sample exhibits a desirable thermoelectric performance of zT max ∼ 1.81 at 623 K and zT ave ∼ 1.01 between 300 and 723 K. This study showcases an effective doping strategy for enhancing the thermoelectric properties of GeTe-based materials by decoupling phonon and carrier scattering.