Role of interfaces in organic–inorganic flexible thermoelectrics

Abstract

The interface is always a critical factor affecting thermoelectric performance in composite systems. However, understanding the electrical and thermal transport behaviors at the interfaces has been a long-standing challenge. Here, we advance this understanding by using spatially resolved current and thermal measurements in single wall carbon nanotubes (CNTs)-Tellurium-poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT:PSS) nanocomposites. Our results indicate that the obtained ultra-low thermal conductivity in such nanocomposites with high CNTs content can be understood by the interface thermal resistance and interface density of the clusters, which is directly confirmed by quantitative mappings of thermal conductivity in the micro-scale interface regions via scanning thermal microscopy. Furthermore, the highly conductive layers can be formed at the interfaces of Te - PEDOT:PSS and CNTs - PEDOT:PSS revealed by high-resolution local conductivity and topography mapping, leading to simultaneous enhancement of electrical conductivity and Seebeck coefficient. Ultimately, a power factor of 224 µW/mK 2 , as well as an ultralow in-plane thermal conductivity of 0.39 W/mK at 410 K, has been achieved by tuning carrier mobility and phonon scattering using multiple polymer-inorganic interfaces. The ZT value reaches up to 0.24 at 410 K and a planar flexible thermoelectric generator exhibits excellent output power of 1.33 μW and highly competitive normalized maximum power density of 0.26 W/m at a temperature difference of 67.8 K These approaches give deep insights to understand the interface role in nanocomposites, and also attests to the great potential of using such organic–inorganic composites in wearable electronics. We design the multiple interfaces co-existence in CNTs-Te-PEDOT:PSS nanocomposite, the electrical and thermal properties remain decoupled and have been optimized greatly due to the different mechanisms of induced highly conductive layers and strong phonon scattering at multiple polymer-inorganic interfaces. The local electric and thermal behaviors at interfaces has also been revealed by straightforward methods. • The electrical conductivity and Seebeck coefficient are decoupled due to the enhanced mobility at multiple interfaces. • Ultralow in-plane thermal conductivity (0.39 W/mK) has been achieved even in sample with 60 wt% CNTs. • Direct investigations on electric and thermal behaviors at the interface regions are carried out via c-AFM and SThM. • The prepared flexible TE module exhibits competitive outpower comparing with other organic-inorganic TE generators.