Interface-Engineered High-Performance Flexible Thermoelectric Films for Self-Powered Health Monitoring

Harvesting low-grade discrete heat through flexible thermoelectrics (TEs) offers a transformative route toward self-powered wearable electronics, yet is hindered by the inherent trade-off among electrical/thermal transport and flexibility, as well as lack of application-driven co-design between materials and devices. Herein, we counterintuitively incorporate an insulating polymer-polyvinylpyrrolidone (PVP) into the flexible Ag₂Se-based matrix, leveraging its multifunctional interfacial effects to achieve carrier-phonon decoupling. This yields a flexible TE film with record-high power factor of 3328 ± 332 µW m^-1 K^-2 and a figure of merit (ZT) of 1.1 at 341 K. The high-performance stems from the rational incorporation of PVP as a dual-functional additive, which simultaneously promotes coherent grain boundaries and mitigates Fermi-level pinning effect. The assembled flexible TE generator delivers a normalized power density of 81 W m^-2 under a temperature gradient of 35 K. Moreover, a proof-of-concept TE-cup that integrates physiological sensing and energy harvesting is demonstrated, which achieves 100%-accurate user identification via thermal-sensing signals and powers a physiological monitor using harvested energy (∼20 mV) through an ultra-low-power management circuit. Our work redefines the positive role of non-conductive polymers in TE nanocomposites, establishes an effective strategy for structure-property manipulation, and pioneers a self-sustained platform for next-generation healthcare monitoring.