Enhanced Thermoelectric Performance in Zn_1–xCd_xSb (x = 0–0.375) Solid Solutions by Dynamic Optimization of Charge Carrier Concentration

Abstract

ZnSb is a promising thermoelectric (TE) material due to its decent TE conversion efficiency and low cost. However, its full potential for TE applications has not been achieved due to difficulties associated with optimal doping and its unique temperature-dependent charge carrier concentration (n). In this work, we propose a codoping strategy that enables precise control of n, leading to dynamic optimization of the charge carrier concentration. The codoping technique works on the principle of charge compensation between the acceptor impurities and charged vacancies (VZn) which are present in this system. Utilizing this technique, we show that the peak zT (TE figure-of-merit) value in ZnSb can be raised to 1.22 (at 645 K). Further improvement in the TE performance is demonstrated by Cd substitution, which facilitates preferential scattering of phonons and thereby reduction of lattice thermal conductivity. This results in a peak zT value of 1.41 (at 550 K), which is comparable to other state-of-the-art materials in this temperature range. Theoretical estimates of the TE conversion efficiencies indicate values of ηmax = 10% for ZnSb and 12.2% for the Cd-substituted systems, highlighting their potential for TE applications.