n-type thermoelectric material Mg₂Sn_0.75Ge_0.25 for high power generation

Thermoelectric power generation is one of the most promising techniques to use the huge amount of waste heat and solar energy. Traditionally, high thermoelectric figure-of-merit, ZT, has been the only parameter pursued for high conversion efficiency. Here, we emphasize that a high power factor (PF) is equivalently important for high power generation, in addition to high efficiency. A new n-type Mg₂Sn-based material, Mg₂Sn_0.75Ge_0.25, is a good example to meet the dual requirements in efficiency and output power. It was found that Mg₂Sn_0.75Ge_0.25 has an average ZT of 0.9 and PF of 52 μW·cm^-1·K^-2 over the temperature range of 25-450 °C, a peak ZT of 1.4 at 450 °C, and peak PF of 55 μW·cm^-1·K^-2 at 350 °C. By using the energy balance of one-dimensional heat flow equation, leg efficiency and output power were calculated with T_h = 400 °C and T_c = 50 °C to be of 10.5% and 6.6 W·cm^-2 under a temperature gradient of 150 °C·mm^-1, respectively.