Ultra-flexible self-supporting Ag2Se/nylon composite films for wearable thermoelectric devices

Recently, flexible thermoelectric (TE) generators (f-TEGs) have received a lot of attention. Compared with TE films on flexible substrates, self-supporting composite films prepared by combining TE materials with soft fabrics and thus retaining the inherent advantages of fabrics, such as stretchability, breathability, and flexibility, are more practical and may significantly expand the application of f-TEGs in smart wearable devices. Hence, in this work, a facile and rapid method for preparing ultra-flexible self-supporting Ag2Se/nylon composite films is developed. The composite films with both TE properties and flexibility were obtained by fast selenization of commercial Ag/nylon fiber fabrics in a short time (60 s) at room temperature and then hot pressing at 230 °C in a vacuum. The maximum power factor of an optimized composite film at room temperature can reach 73.7 μW m−1 K−2. Meanwhile, the film exhibits excellent flexibility with the Seebeck coefficient and electrical conductivity decreased by only 7.37 and 8.48% after being bent 4000 repetitions around a round bar with a radius of 4 mm, which exceeds most reported flexible TE films. The ultra-high flexibility is mainly attributed to its high content of the nylon matrix (∼85.05 wt%), the tight bonding between Ag2Se grains, and the good combination between the Ag2Se and nylon matrix. In addition, a 3-leg f-TEG assembled with the optimal film produces a maximum power of ∼1.524 μW (corresponding to a power density of ∼0.47 W m−2) at a temperature gradient of 40.6 K, verifying the good TE performance of the composite film. This f-TEG can also be used as a self-powered temperature sensor, showing potential applications in daily life.