High Thermoelectric Performance in Ag₂Se Films Enabled by Large Carrier Mobility

Flexible Ag 2 Se thin films are promising substitutes for Bi 2 Te 3 owing to their excellent room-temperature thermoelectric performance and flexibility. However, they generally exhibit poor electrical transport properties because their in-plane mobility is weakened. Optimizing grain size can improve mobility, but it may also impact thermal transport properties. In this study, Ag 2 Se thin films with enhanced carrier mobility were fabricated by selenizing Ag precursor films that were predeposited by magnetron sputtering. By varying the sputtering power, the grain size of Ag 2 Se films was controlled. The optimized film shows an extraordinary carrier mobility of 1521 cm 2 V –1 s –1 and an improved power factor of 25.15 μW cm –1 K –2 at room temperature. Simultaneously, due to numerous defects (e.g., dislocations and low-angle grain boundaries) caused by the nonequilibrium preparation process, the optimized thin film still maintains a low thermal conductivity, resulting in an excellent ZT of 0.83 at RT. Meanwhile, the film also shows outstanding flexibility (99% of the initial electrical conductivity is maintained after 1000 bending cycles with a bending radius of 4 mm). The 3-leg flexible TEG demonstrates a maximum power density of 52.62 W m –2 at a temperature difference of 30 K, showing potential applications in powering generation for wearable electronics.