Stretchable p/n-Pair Thermoelectric Fibers Based on Core (Ag)–Shell (Ag₂Se) Structure for Wearable Electronics

The development of stretchable p/n-pair thermoelectric (TE) fibers holds significant promise for multifunctional wearable electronics, yet remains challenging due to complex processing and limited mechanical durability. Here, a novel strategy is presented for the facile fabrication of stretchable Ag@Ag₂Se-based TE fibers using a selective in situ chemical reduction process, eliminating the need for thermal treatment or specialized equipment. The resulting fibers feature a robust core–shell architecture, with conductive Ag cores and n-type Ag₂Se shells, achieving a Seebeck coefficient of −96.75 µV K⁻¹ under 100% strain and stable electrical conductivity under 200% strain. Notably, the fibers exhibit excellent cyclic stability with ΔV/V₀ maintained within 1.75% under mechanical deformation. When patterned into p/n-pair arrays through localized chemical treatment, the fibers function as efficient energy harvesters and strain/temperature sensors. Integrated into wearable platforms, these fibers demonstrate simultaneous mechanical and thermal sensing and effective energy harvesting from body heat. This work establishes a versatile platform for scalable, miniaturized, and multifunctional TE fiber systems, advancing the future of smart textiles and wearable electronics.