Regioisomeric Cyanated Polythiophenes Bearing Polar Side Chains for n-Type Organic Thermoelectrics

Abstract

The development of n-type polymers with high thermoelectric performance remains a major challenge for organic thermoelectrics. Herein, by devising two new isomeric cyano-functionalized bithiophene building blocks bearing polar side chains, we report two novel donor–acceptor-configurated n-type polythiophene polymers (BTOgCN-FT and BTCNOg-FT) with regiochemically tuned intramolecular S···O noncovalent interactions (INIs) and cyanation patterns for n-type thermoelectric application. The results show that cyanation furnished low-lying LUMO energy levels approaching that of the benchmark n-type polymer N2200 for both polymers (∼−3.90 eV), which combine with their polar side chain-enabled high dopant miscibility, leading to efficient n-doping efficiencies. Detailed theoretical and experimental studies also suggest that BTOgCN-FT exhibited a more planar backbone conformation and more ordered interchain packing in film state, thus yielding higher electrical values than BTCNOg-FT. Therefore, the polymer BTOgCN-FT eventually displays an optimal power factor (PF) value of 2.77 μW m–1 K–2, which is higher than that of BTCNOg-FT (1.50 μW m–1 K–2) and also largely outperforming that of the thoroughly investigated and optimized polymer N2200 (typical PF value of 10–2 μW m–1 K–2). Our work not only presents two novel structurally simple and isomeric electron-accepting building blocks but also offers valuable structure–property correlations for the future design of high-performance n-type thermoelectric materials.