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 Ag2Se and Ag2Se–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 Ag2Se/nylon and Ag2Se–CuAgSe/nylon films. The cold-pressed TE films could retain the TE properties of bulk samples, and hence, a power factor of ∼1286 μW/mK2 at 300 K is achieved for the Ag2Se/nylon film, the highest value among those reported for Ag2Se/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 Ag2Se–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.