Hierarchical Architectural Structures Induce High Performance in n‐Type GeTe‐Based Thermoelectrics

Compatible p- and n-type materials are necessary for high-performance GeTe thermoelectric modules, where the n-type counterparts are in urgent need. Here, it is reported that the p-type GeTe can be tuned into n-type by decreasing the formation energy of Te vacancies via AgBiTe2 alloying. AgBiTe2 alloying induces Ag2Te precipitates and tunes the carrier concentration close to the optimal level, leading to a high-power factor of 6.2 µW cm−1 K−2 at 423 K. Particularly, the observed hierarchical architectural structures, including phase boundaries, nano-precipitates, and point defects, contribute an ultralow lattice thermal conductivity of 0.39 W m−1 K−1 at 423 K. Correspondingly, an increased ZT of 0.5 at 423 K is observed in n-type (GeTe)0.45(AgBiTe2)0.55. Furthermore, a single-leg module demonstrates a maximum η of 6.6% at the temperature range from 300 to 500 K. This study indicates that AgBiTe2 alloying can successfully turn GeTe into n-type with simultaneously optimized thermoelectric performance.