Engineering Thermal Conductivity for Balancing Between Reliability and Performance of Bulk Thermoelectric Generators

The nanostructuring approach has significantly contributed to the improving of thermoelectric figure-of-merit (ZT) by reducing lattice thermal conductivity. Even though it is an effective method to enhance ZT, the drastically lowered thermal conductivity in some cases can cause thermomechanical issues leading to decreased reliability of thermoelectric generators. Here, an engineering thermal conductivity (kappa(eng)) is defined as a minimum allowable thermal conductivity of a thermoelectric material in a module, and is evaluated to avoid thermomechanical failure and thermoelectric degradation of a device. Additionally, there is dilemma of determining thermoelectric leg length: a shorter leg is desired for higher W kg(-1), W cm(-3), and W $(-1), but it raises the thermomechanical vulnerability issue. By considering a balance between the thermoelectric performance and thermomechanical reliability issues, it is discussed how to improve device reliability of thermoelectric generators and the engineering thermal conductivity of thermoelectric materials.