High-performance n-type PVDF/Ag₂Se Free-standing Flexible Composite Thermoelectric Films Fabricated by Powder Hot-pressing

Rapid development of applications in wearable devices, microelectronics, and internet of things has created an urgent demand for free-standing flexible thermoelectric films. Currently, research on n-type free-standing flexible thermoelectric films significantly lags behind, and there is an urgent need to enhance film performance through the optimization of preparation processes. In this study, high-performance n-type poly(vinylidene fluoride)/silver selenide (PVDF/Ag2Se) free-standing flexible thermoelectric composite films were developed using a simple and efficient powder hot-pressing method. The high-temperature and high-pressure conditions during hot pressing induced recrystallization and grain growth of Ag2Se, effectively reducing grain boundary density, significantly decreasing carrier scattering and interfacial resistance, thereby simultaneously enhancing carrier mobility, electrical conductivity and Seebeck coefficient. Meanwhile, the melted PVDF filled interstices of the Ag2Se conductive network during hot pressing, substantially improving material flexibility while increasing density. Experimental results demonstrate that the hot-pressed sample with 80% (in mass) Ag2Se exhibits outstanding room-temperature thermoelectric performance with an electrical conductivity of 277.0 S·cm-1 and a Seebeck coefficient of -135 μV·K-1, and thermoelectric power factor (PF) and estimated figure of merit (ZT) reach 509 μW·m-1·K-2 and 0.26, respectively. This performance not only significantly surpasses that of previously reported PVDF/Ag2Se free-standing films but also ranks among the highest for all reported Ag2Se-based organic/inorganic free-standing flexible thermoelectric films. Furthermore, mechanical tests reveal that the film maintains over 92% of its original conductivity after 500 bending cycles at a 5 mm radius, while exhibiting a maximum tensile strain four times greater than pure Ag2Se films. This study provides a novel strategy for synergistic optimization of thermoelectric performance and mechanical flexibility in organic/inorganic composite thermoelectric materials.