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

ABSTRACT 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 Ag 2 Se‐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.