Systematic Investigation of Solution-State Aggregation Effect on Electrical Conductivity in Doped Conjugated Polymers

Abstract

The mesoscopic solution-state aggregation plays a dominant role in the multilevel self-assembly of conjugated polymers. However, its effect on solid-state microstructures and the electrical performance of conjugated polymers is still a puzzle due to the limitation of characterization techniques. Herein, we have developed four isoindigo-based conjugated polymers with varied alkyl chains to reveal the relationship between solution-state aggregation, molecular doping process, and charge transport properties. For the solution-state aggregation, the photophysical and microstructural characterizations were adopted to explore the solvated aggregation structures of these four polymers, where well-differentiated aggregate sizes were observed. IIDDT-C3 showed small solvated aggregate sizes but excellent aggregate connectivity in solutions. The characterization of the solid-state microstructure demonstrated that IIDDT-C3 had ideal crystalline solid-state microstructures with densely fibrillar morphology, which endowed IIDDT-C3 with the highest electrical conductivity up to 531 ± 50 S cm−1 after doping among these four polymers. Our work provides molecular guidance for clarifying the structure–performance relationship between aggregation structures and the electrical properties of the doped conjugated polymers with different alkyl chains.