Enhanced Thermoelectric Performance in Flexible Sulfur-Alloyed Ag₂Se Thin Films

Flexible thermoelectric generators can directly convert thermal energy harvested from the human body into electricity. The Ag₂Se flexible film, a promising material for wearable thermoelectric generators, normally demonstrates an inferior electrical transport property due to its weakened in-plane mobility. In this study, the in-plane electrical transport properties of flexible Ag₂Se films were optimized by alloying with additional sulfur. This optimization is achieved by leveraging the differences in elemental electronegativity and the preferred orientation of the Ag₂Se films. The sulfur-alloyed Ag₂Se thin film, with a nominal ratio of 3 atom %, can reach a maximum mobility of 1150 cm^-2 V^-1 s^-1 at 300 K. So, the optimized room-temperature power factor increases to 1935 μW m^-1 K^-2. Furthermore, the Ag₂Se film alloyed with 3 atom % sulfur exhibits excellent flexibility even after 1000 bending cycles with a radius of 5 mm, characterized by a relative resistance increment of less than 3%. In addition, the corresponding π-type flexible thermoelectric generator possesses a maximum power density of 51 W m^-2 at a temperature difference of 50 K.