Tunable p- and n-Type Tellurium-Free Mg3Bi2 Thermoelectric Thin Films by Thermal Coevaporation

Mg3Bi2 has recently emerged as a promising environmentally friendly alternative to bismuth tellurides for near-room-temperature thermoelectrics. Here, we report on the fabrication of Mg3Bi2 thin films under Mg-rich and Mg-poor conditions via vacuum thermal coevaporation. We demonstrate that under Mg-deficient conditions thin films show a p-type conduction behavior with a maximum power factor exceeding 300 μW m–1 K–2 and a thermoelectric figure of merit ZT of 0.11 at 200 °C. Increasing the amount of Mg enables the formation of Mg-rich Mg3Bi2 thin films with n-type conduction. These films exhibit a maximum power factor and ZT at lower temperatures of around 130–140 °C. Moreover, the maximum ZT is increased to 0.19 due to the ultralow thermal conductivity of the n-type Mg3Bi2.