Flexible elemental thermoelectrics with ultra-high power density

Flexible thermoelectrics have attracted great attention due to their potential to convert waste heat to electricity to power wearable devices and IoT (Internet of things) sensors. Though organic thin-film thermoelectric materials are popular choice for preparing flexible thermoelectrics, they suffer from low thermoelectric performances due to the low figure of merit zT . In this work, we demonstrate a new strategy to design high-performance thermoelectrics by highlighting the influence of power factors instead of zT . To verify our claim, thermoelectric is prepared through sputtering high-power factor but low zT elemental thin films of Sb (p-type) and Ni (n-type) on a polyimide substrate. In this system, ascribed by the high-power factor (up to 7 mW/mK 2 ), a high power density of up to 4.7 mW/cm 2 at a temperature gradient of 50 K can be achieved, even with the low zT (<0.1). In addition, finite element method (FEM) analysis shows that the benefit of high-power factor increases with decreasing film thicknesses. Our results show that in the case of organics and inorganics thin films, maximizing power factor is more important than maximizing zT . This finding serves to guide the design paradigm of thermoelectrics for wearable devices and is useful for the broad organic electronics community. • Ultra-high power density of up to 4.7 mW/cm 2 at a temperature gradient of 50 K. • Importance of power factor in planar thin film thermoelectrics. • Shifting paradigm to elemental thermoelectrics for flexible applications. • Low thermal conductivity substrate plays vital role.