Thermal Evaporation Method for Preparing Ag₂Se Flexible Thin Films and Devices

The burgeoning development of wearable devices has spurred an urgent demand for green and efficient power supply solutions, propelling miniaturized flexible thermoelectric generators to the forefront of research. Nevertheless, the performance constraints of thermoelectric materials and intricate device design challenges remain formidable barriers to technological advancement in this field. Silver selenide (Ag₂Se), a highly promising thermoelectric material, exhibits room-temperature performance comparable to that of the conventional bismuth telluride (Bi₂Te₃), thereby offering novel opportunities for the development of flexible thermoelectric devices. In this work, Ag₂Se thin films were synthesized on polyimide (PI) substrates via thermal evaporation. By systematically varying the annealing temperature, we achieved precise control over the preferred (013) orientation of the Ag₂Se films. The film annealed at 453 K, with a thickness of 580 nm, demonstrated a maximum power factor of 14.87 μW/(cm·K²). Subsequent post-selenization treatment was applied to further optimized the composition of the Ag₂Se thin films, elevating the power factor to 19.13 μW/(cm·K²). Based on the optimized thin films, an Ag₂Se-Ag single-leg flexible thermoelectric generator was fabricated. Under a temperature gradient of 40 K, the device delivered a maximum output power of 235.2 nW. Notably, the flexibility of the device was significantly improved by introducing a spin-coated poly (vinyl laurate) organic layer. It retained over 90% of its initial performance after 1000 repeated bending cycles at a small radius of 6 mm. These findings collectively underscore the substantial potential of Ag₂Se devices prepared via thermal evaporation for applications in wearable power generation.