Enhancing Charge Transport Performance of n-Doped Conjugated Polymers by Customizing Amphipathic Side Chains

The charge transport performance of n-doped conjugated polymers is mainly limited by low charge mobility and insufficient charge carrier density. Research efforts in side-chain engineering are still lacking compared to backbone studies, and there is a need to achieve a deeper understanding of the relationship between the side-chain structure and polymer properties. Our report found that the doping efficiency and charge mobility of n-doped conjugated polymers can be improved by customizing the amphipathic side chains. We synthesized three conjugated polymers with a naphthalenediimide core and amphipathic side chains of varying ethylene glycol end group lengths. Increasing the length of the ethylene glycol end group led to higher polarity of the conjugated polymer and a more extended conformation of the side chains in the solution. This resulted in enhanced π-stacking of the polymer chain and improved host-dopant miscibility, facilitating high charge carrier mobility and doping efficiency. However, the insulating side chains diluted the charge transport pathways. The best thermoelectric performance (σ = 2.76 S cm–1 and PF ≈ 28.4 μW m–1K–2) and the highest figure-of-merit μC* of 25 F cm–1V–1s–1 were achieved when the number of ethylene glycol units was four. Our study demonstrates the potential of tailoring amphipathic side chains to enhance electron transport in extrinsically doped conjugated polymers. It provides valuable guidance for the design of advanced n-type OTE and OECT materials.