Understanding Effects of Alkyl Side-Chain Density on Polaron Formation Via Electrochemical Doping in Thiophene Polymers

Stewart, K. and Pagano, K. and Tan, E. and Dabóczi, Mátyás and Rimmele, M. and Luke, J. and Eslava, S. and Kim, J.-S. (2024) Understanding Effects of Alkyl Side-Chain Density on Polaron Formation Via Electrochemical Doping in Thiophene Polymers. ADVANCED MATERIALS, 36 (20). No. -2211184. ISSN 0935-9648

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Abstract

Polarons exist when charges are injected into organic semiconductors due to their strong coupling with the lattice phonons, significantly affecting electronic charge-transport properties. Understanding the formation and (de)localization of polarons is therefore critical for further developing organic semiconductors as afuture electronics platform. However, there are very few studies reported in this area. In particular, there is no direct in situ monitoring of polaron formation andidentification of its dependence on molecular structure and impact on electrical properties, limiting further advancement in organic electronics. Herein, howa minor modification of side-chain density in thiophene-based conjugated polymers affects the polaron formation via electrochemical doping, changing the polymers’ electrical response to the surrounding dielectric environment for gas sensing, is demonstrated. It is found that the reduction in side-chain density results in a multistep polaron formation, leading to an initial formation of localized polarons in thiophene units without side chains. Reduced side-chain density also allows the formation of a high density of polarons with fewer polymer structural changes. More numerous but more localized polarons generate a stronger analyte response but without the selectivity between polar and nonpolar solvents, which is different from the more delocalized polarons that show clear selectivity. The results provide important molecular understanding and design rules for the polaron formation and its impact on electrical properties.

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