Bipolar Suppression for High Performance n-Type GeTe-Based Thermoelectrics

Stable operation of thermoelectric devices requires both p- and n-type materials with desirable compatibility and similar application temperature range. However, n-type GeTe-based materials currently have a lower application temperature range (<525 K) than p-type GeTe-based materials (500–800 K) due to the strong bipolar effect. Here, it is demonstrated that the bipolar effect of n-type GeTe can be inhibited by the combination of bandgap enlargement and minority carrier filtering. Specifically, reducing cation vacancies can enlarge the bandgap, while introducing localized heavy doping areas with relatively large bandgap can generate a minority carrier barrier in the valence band to block the minority carrier transport. Consequently, a record-high power factor (5.3 µW cm⁻¹ K⁻²) and figure-of-merit (zT) of 0.45 can be obtained at 723 K in n-type Ge_0.46Bi_0.17Pb_0.37Te_0.7Se_0.3. This work demonstrates that bipolar suppression is an effective strategy to realize high-performance n-type GeTe-based materials in the mid-temperature range, and correspondingly extends the applicability.