Pressure-free sintering of high-performance crystalline/amorphous Ag2S0.5Te0.5/nylon films for flexible thermoelectric devices

Abstract

Ag₂(S,Te) compounds exhibit excellent thermoelectric (TE) performance and unique mechanical properties, making them an ideal system for near-room-temperature flexible TE materials. In response to the current issues of complex preparation processes and high energy consumption for this kind of material, this work proposes a fabrication strategy for Ag₂(S,Te)-based flexible TE films (f-TEFs). Ag₂S_0.5Te_0.5 powders were first synthesized via a wet-chemical method, followed by deposition onto a nylon substrate by vacuum-assisted filtration, and were finally subjected to pressure-free sintering. An optimized composite film exhibits a power factor of 516 µW m⁻¹ K⁻² at room temperature (RT), which ranks among the higher levels compared with other Ag₂(S,Te)-based f-TEFs. Microstructural characterization studies show that the film contains amorphous/crystalline phases, with numerous nano-pores and wrinkled stacking faults. This unique phase composition and structural configuration synergistically result in multi-scale phonon scattering, which efficiently suppresses lattice thermal conductivity to 0.27 W m⁻¹ K⁻¹ and ultimately contributes to a RT ZT value of 0.34. Additionally, the film retains 93% of its initial electrical conductivity after 1500 bending cycles around a 4 mm-radius rod. A four-leg flexible TE device assembled based on this film generates an open-circuit voltage of 13.5 mV and a maximum output power of 0.84 µW at a ΔT of 30 K, respectively. This work provides a novel approach for efficient and low-cost preparation of high-performance Ag₂(S,Te) f-TEFs, showing great potential for long-term TE power generation and thermal sensing, thus pushing flexible electronics for practical applications.