Impact of Chain Conformation and Interchain Contacts on Charge Transport in Conjugated Polymers

Charge transport in organic semiconductors such as conjugated polymers proceeds through a combination of intrachain and interchain charge transfer events. Predicting transport properties for any new material requires an understanding of how the chemical structure and physical organisation of polymer chains influence these two processes. The polymer’s conformational phase space influences intrachain charge dynamics through variations in the structure, and hence energy, of polaron states and also influences the type of interchain contacts that can be formed. We consider the case of the stiff, high-mobility indacenodithiophene-<i>co</i>-benzothiadiazole polymer (C16-IDTBT) and use a variety of electrical and structural measurements as well as molecular dynamics, electronic structure calculations and charge transport simulations to probe the nature of the intra and inter-chain charge transfer processes. We conclude that the polymer’s unusually high connectivity, rather than high interchain coupling, is responsible for its hole mobility. We compare the behaviour with other conjugated polymers including polyfluorenes and polythiophenes, in terms of their chemical structure. We conclude by reviewing the factors that will ultimately limit charge transport in conjugated polymers.