Molecular dopants regulate structural disorder of DPP-based conjugated polymer toward high-performance n-type organic thermoelectrics.

Abstract

Molecular doping has become the dominating strategy to optimize the performance of organic thermoelectrics (OTEs). While effective, this method remains largely limited by the inverse relationship between the components of the thermoelectric figure of merit, namely the electrical conductivity (?) and the Seebeck coefficient (?). Increasing the charge carrier density via molecular doping is beneficial for ? but detrimental for ?. Novel n-type conjugated polymers display improved ? since their chemical structure allows enhanced doping efficiencies however, this often leads to a quick decrease in ?. In this work, we demonstrate that careful selection of a host-dopant system leads to reduced structural disorder and increased anisotropy, resulting in high ? with minimal reduction of ?. We blend the n-type conjugated polymer 2DPP-2CNTVT with three state-of-the-art n-type dopants: TBAF, N-DMBI, and TAM. TBAF and TAM show conventional trends i.e., only high ? or only high ? respectively. On the other hand, N-DMBI shows high values for both parameters achieving an n-type power factor of 99.3 ?Wm-1K-1. GIXRD assessment demonstrates that N-DMBI doping increases the film crystallinity and changes the original bimodal orientation to a preferential edge-on orientation. This remarks the importance of host-dopant matching and provides a roadmap to decouple the ?-? inverse relationship toward realizing high-performance OTEs.