High-Performance Selenide-Based Flexible Thermoelectric Films

Flexible thermoelectric (TE) devices hold unique promise for future wearable electronics. However, the development of flexible thermoelectrics for wearable electronics is still a challenge owing to their low power conversion efficiency and degradation due to repeated bending on human body curvature. Herein, we have developed flexible TE films using inorganic Ag 2 Se and Ag 2 Se–CuAgSe on nylon through the chemical route followed by cold pressing to see the effect of the processing route on the flexibility and TE properties of Ag 2 Se/nylon and Ag 2 Se–CuAgSe/nylon films. The cold-pressed TE films could retain the TE properties of bulk samples, and hence, a power factor of ∼1286 μW/mK 2 at 300 K is achieved for the Ag 2 Se/nylon film, the highest value among those reported for Ag 2 Se/nylon so far. The processed TE films show excellent flexibility against bending up to 1500 cycles without much degradation in the film conductivity. A TE prototype fabricated out of the processed Ag 2 Se–CuAgSe/nylon film generates the output voltage and power of 9 mV and 110 nW, respectively, at 300 K when a temperature gradient of 20 K is applied across it. The prototype could produce a 1.2 mV output voltage in contact with a human wrist at a temperature difference of ≤5K. The obtained output voltage at such a low temperature gradient using human body heat is the highest among the reported values until now, which can be attributed to the enhanced TE properties of the cold-pressed film. Our findings pave the way to developing highly efficient flexible inorganic/organic thermoelectrics for near-room-temperature energy harvesting.