Enhanced thermoelectric performance from self-assembled alkyl chain-linked naphthalenediimide/single walled carbon nanotubes composites

Abstract

Naphthalenediimide (NDI) derivatives with high electron affinity and strong π–π stacking interactions have been frequently used as electro-active materials in the field of organic optoelectronic materials. However, the out of control feature of the aggregate states of NDI derivatives often lead to their poor performance for thermoelectric applications. Herein, taking the advantage of van der Waals forces intermolecular interactions, alkyl chain-linked NDIs with H-(J-) aggregates through self-assembly were successfully achieved. The NDI-based polymer linked with a decyl chain (NDI-10) showed J-aggregate, in which the intrachain electronic coupling was dominated and the polymer linked with a butyl chain (NDI-4) and a hexyl chain (NDI-6) reviewed H-aggregate, in which interchain coupling was dominated, the hypothesis was confirmed by results of fluorescence, SAXS, and XRD. The different H-(J-) aggregates affects carrier transport in a two-dimensional transmission channel in our polymers. Moreover, by utilizing the high electrical conductivity of single-walled carbon nanotubes (SWCNTs), we achieved high-performance thermoelectric (TE) composites containing SWCNTs and the polymers based on the alkyl chain-linked NDIs. The obtained composites displayed enhanced TE performance with a high power factor of 238 ± 21 μW m−1 K−2 at 300 K. The corresponding TE module consisting of ten p-type junctions reaches a large output voltage of 5.82 mV and an output power of 28 nW under a 30 K temperature difference. This design strategy promotes the future fabrication of high-performance TE materials and modules.