Device-level optimization of n-type Mg₃(Sb, Bi)₂-based thermoelectric modules toward applications

The performance of thermoelectric materials has been significantly increased in recent decades, making the concept of generating energy from waste heat or enhancing refrigeration more feasible. N-type Mg₃(Sb, Bi)₂ material is one of the most popular and commercially promising materials in the thermoelectric family, however, there are significant challenges at the device level toward large-scale applications. First, it is always challenging to maintain high zT values over a wide temperature range. Second, the zT of the material is not directly equivalent to the zT of the device because the real zT of the device is affected by the contact resistances at the junctions. Third, reliability and durability issues are concerns since they critically determine the service life of the devices. Fourth, proper structure design, including size match of the n- and p-type thermoelectric legs, heat exchange, and space utilization, is crucial to the device’s performance since its efficiency is sensitive to its dimensions. Finally, the manufacturing costs of thermoelectric devices are equally important when considering large-scale applications. In short, the figure of merit zT is of great significance as a core parameter to guide the improvement of thermoelectric materials while the thermoelectric field must look far beyond the simple goal of pursuing high zT. Here, we focus on n-type Mg₃(Sb, Bi)₂-based thermoelectric modules and try to find out the influence of various parameters on the module and device-level optimization strategies to solve practical application issues.