Increasing H-Aggregates via Sequential Aggregation to Enhance the Hole Mobility of Printed Conjugated Polymer Films
Yin Wu, Zicheng Ding, Qiang Zhang, Xiao Liang, Hua Yang, Wenliang Huang, Yueling Su, Yi Zhang, Hanlin Hu, Yanchun Han, Shengzhong Liu, Kui Zhao
Abstract
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.