High‐Performing Flexible Mg3Bi2 Thin‐Film Thermoelectrics

With the advances in bulk Mg₃Bi₂, there is increasing interest in pursuing whether Mg₃Bi₂ can be fabricated into flexible thin films for wearable electronics to expand the practical applications. However, the development of fabrication processes for flexible Mg₃Bi₂ thin films and the effective enhancement of their thermoelectric performance remain underexplored. Here, magnetron sputtering and ex-situ annealing techniques is used to fabricate flexible Mg₃Bi₂ thermoelectric thin films with a power factor of up to 1.59 µW cm^-1 K^-2 at 60 °C, ranking as the top value among all reported n-type Mg₃Bi₂ thin films. Extensive characterizations show that ex-situ annealing, and optimized sputtering processes allow precise control over film thickness. These techniques ensure high adhesion of the films to various substrates, resulting in excellent flexibility, with <10% performance degradation after 500 bending cycles with a radius of 5 mm. Furthermore, for the first time, flexible thermoelectric devices are fabricated with both p-type and n-type Mg₃Bi₂ legs, which achieve an output power of 0.17 nW and a power density of 1.67 µW cm^-2 at a very low temperature difference of 2.5 °C, highlighting the practical application potential of the device.