Wearable Thermoelectric Generators Based on Flexible Ag₂Se/PVDF Films: Influence of Film Geometry and Wind on Energy Harvesting

In wearable thermoelectric generators (TEGs), the challenge is to develop thermoelectric materials that are both high-performance and mechanically flexible. Here, we present a flexible n-type Ag₂Se/poly(vinylidene fluoride) (PVDF) composite film that simultaneously achieves enhanced thermoelectric figure of merit (<i>zT</i>) and improved flexibility. A freestanding Ag₂Se film incorporating 5 wt % PVDF reached a <i>zT</i> of 0.591 at room temperature (versus 0.529 for pure Ag₂Se) and a minimum bending radius of 3.5 mm (improved from 6 mm), and it maintained its performance over 1000 bending cycles. The performance enhancement is attributed to a uniform dispersion of PVDF within the Ag₂Se matrix, which greatly reduces lattice thermal conductivity via interfacial phonon scattering. We integrated the n-type Ag₂Se/PVDF and p-type single-walled carbon nanotube/PVDF films into a vertical wearable TEG architecture that leverages out-of-plane (through-thickness) thermal gradients. The resulting device generated power from a small skin-to-ambient temperature difference (∼10 °C) and exhibited significantly increased output under mild airflow or motion. This work demonstrates a viable strategy for harvesting body heat using flexible high-<i>zT</i> materials in a device design optimized for low-grade thermal energy.