Improvement in Solubility and Molecular Assembly of Cyclopentadithiophene-Benzothiadiazole Polymer

Using linear side chains for conjugated polymers is hindered by their limited solubility in common organic solvents, creating problems during purification and processing, whereas branched alkyl chains generally preclude interchain interdigitation because their bulkiness usually hinders interchain interactions. To compensate the adverse effects from each side chain, it is shown that replacing commonly employed 2‐ethylhexyl (2EH) solubilizing groups with branched 5‐ethylnonyl (5EN) chains not only improves solution processability to PCDT‐BT polymer, but also induces an advantageous change in polymer self‐assembly and backbone orientation in thin films that correlates with an increase in transistor performance. Use of the newly designed branched 5‐ethylnonyl (5EN) chain provides a satisfactory processability to the PCDT‐BT polymer without disrupting the π–π interactions, accompanied by an advantageous change in polymer self‐assembly and backbone orientation, leading to a superior mobility, in comparison to that of the reference polymer.