Step-Up Thermoelectric Performance Realized in Bi2Te3 Alloyed GeTe via Carrier Concentration and Microstructure Modulations

We report that outstanding thermoelectric performances can be achieved in 7% Bi2Te3 alloyed GeTe when it is simultaneously doped with iodine and treated with a water quenching process. The introduction of moderate iodine can help optimize the electrical properties; moreover, a water quench treatment was found to induce a novel vacancy microstructure, i.e., Ge vacancy "clusters", which helps to modulate the thermo-electric performance at higher temperatures. The successful combination of these two strategies eventually results in a peak figure of merit ZT similar to 2.2 at 723 K in water quenched Ge0.93Bi0.07Te1.005I0.03. This value is 2-fold of that in pristine GeTe (similar to 1.1). Corresponding average ZT between 323 and 773 K is 1.23, in comparison with 0.44 for pristine GeTe. The calculated single-leg device efficiency of water quenched Ge0.93Bi0.07Te1.005I0.03 is similar to 11.2% at a temperature gradient from 298 to 773 K, suggesting GeTe is a very promising thermoelectric at intermediate-temperature range.