Realizing Ultrahigh Conversion Efficiency of ≈9.0% in YbCd2Sb2/Mg3Sb2 Zintl Module for Thermoelectric Power Generation

Abstract Recently, YbCd 2 Sb 2 ‐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 YbCd 2 Sb 2 ‐based device has yet to be reported. In this work, single‐phase YbCd 1.5 Zn 0.5 Sb 2 is successfully obtained through precise chemical composition control. Then, YbMg 2 Sb 2 ‐alloying increases the cationic vacancy defect formation energy and further optimizes carrier concentration. Moreover, the band structure of YbCd 1.5 Zn 0.5 Sb 2 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 YbCd 1.425 Zn 0.475 Mg 0.1 Sb 2 . Subsequently, choosing Fe 90 Sb 10 as the diffusion barrier layer and adopting the transient liquid phase bonding technique, for the first time, it is demonstrated that YbCd 2 Sb 2 /Mg 3 (Sb, Bi) 2 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 YbCd 2 Sb 2 materials and devices in mid‐temperature heat recovery.