Realizing Ultrahigh Conversion Efficiency of ≈9.0% in YbCdSb/MgSb Zintl Module for Thermoelectric Power Generation.

Recently, YbCdSb-based Zintl compounds have been widely investigated owing to their extraordinary thermoelectric (TE) performance. However, its p orbitals of anions that determined the valence band structure are split due to crystal field splitting that provides a good platform for band manipulation by doping/alloying and, more importantly, the YbCdSb-based device has yet to be reported. In this work, single-phase YbCdZnSb is successfully obtained through precise chemical composition control. Then, YbMgSb-alloying increases the cationic vacancy defect formation energy and further optimizes carrier concentration. Moreover, the band structure of YbCdZnSb is subtly manipulated, and the underlying mechanism is experimentally explored. Combined with the reduced lattice thermal conductivity, a high peak ZT value of ∼1.43 at 700 K is obtained for YbCdZnMgSb. Subsequently, choosing FeSb as the diffusion barrier layer and adopting the transient liquid phase bonding technique, for the first time, it is demonstrated that YbCdSb/Mg(Sb, Bi) TE module with an ultrahigh conversion efficiency of ≈9.0% at a heat difference of 430 K. More importantly, this module displays good thermal stability. This work paves the way for YbCdSb materials and devices in mid-temperature heat recovery.