Increasing H-Aggregates via Sequential Aggregation to Enhance the Hole Mobility of Printed Conjugated Polymer Films

Solid-state microstructures of conjugated polymers are essential for charge transport in electronic devices. However, precisely modulating aggregation pathways of conjugated polymers in a controlled fashion is challenging. Herein, we report a sequential aggregation approach via selectively modulating side chain aggregation in solution state and backbone aggregation during film formation to increase H-aggregates and consequently enhance hole mobility of printed diketopyrrolopyrrole-based polymer (PDPP-TVT) film. The sequential aggregation is realized by introducing 1-bromonaphthalene additive into chloroform solvent. The structural evolution and assembly pathways of PDPP-TVT in initial solution and during printing were revealed using small-angle neutron scattering, cryogenic transmission electron microscopy, and time-resolved optical diagnostics. The results show that the poor interactions between PDPP-TVT side chains and BrN triggers side chain aggregation to form large H-aggregate nuclei in initial solution. The additive further selectively forces backbone aggregation on H-aggregate nuclei during printing with dynamics increasing from ca. 3 to >1000 s. Such prolonged growth window and selective growth of H-aggregates produce large fibers in printed film and therefore 3-fold increase in hole mobility. This work not only provides a promising route toward high-mobility printed conjugated polymer films but also reveals the important relationship between assembly pathways and film microstructure.