Device‐Level ZT Correlation for Validating Single‐Leg Efficiency in GeTe Thermoelectrics

Although numerous high‐ zT GeTe systems have been reported, the correlation between zT and conversion efficiency η remains poorly defined. Reporting peak or even average zT often leads to an overestimation of η as these metrics assume temperature‐independent transport properties—an unrealistic simplification. In 2017, the thermoelectric device ZT for a single material (making either n‐ or p‐type leg) was introduced to evaluate the maximum efficiency of a thermoelectric leg with temperature‐dependent properties. This work provides an experimental validation of Device ZT as a practical metric for predicting thermoelectric conversion efficiency. By combining calibrated single‐leg efficiency measurements, heat‐flow analysis, and finite‐element simulations, we establish a direct correlation between material transport properties, Device zT , and experimentally measured device performance. The CuSb‐GeTe leg achieves an efficiency of 5.4% at ΔT = 400 K, while conventional zT avg ‐based estimates overpredict performance by nearly twofold. In contrast, Device ZT accurately reproduces the measured efficiency. These findings provide an experimentally validated framework for translating material‐level thermoelectric properties into realistic device performance and establish Device ZT as a practical metric for evaluating thermoelectric devices.