Not all aggregates are made the same: Distinct structures of solution aggregates drastically modulate assembly pathways, morphology and electronic properties of conjugated polymers



Tuning structures of solution-state aggregation and aggregation-mediated assembly pathways of conjugated polymers is crucial for optimizing their solid-state morphology and charge transport property. However, it remains challenging to unravel and control the exact structures of solution aggregates, let alone to modulate assembly pathways in a controlled fashion. Herein, we largely modulate aggregate structures by tuning selectivity of the solvent towards the side chain vs. the backbone, which leads to three distinct assembly pathways: direct crystallization from side-chain associated amorphous aggregates, chiral liquid crystal (LC)-mediated assembly from semicrystalline aggregates with side-chain and backbone stacking, random agglomeration from backbone-stacked semicrystalline aggregates. Importantly, we demonstrate for the first time that the amorphous solution aggregates, compared with semicrystalline ones, lead to significantly improved alignment and reduced paracrystalline disorder in solid-state due to direct crystallization during the meniscus-guided coating process. Alignment quantified by dichroic ratio obtained from grazing incidence X-ray diffraction (GIXD) is enhanced by up to fourteen-fold, and the charge carrier mobility increases by a maximum of twenty-fold in films printed from amorphous aggregates compared to those from semicrystalline aggregates. This work shows that by tuning the precise structure of solution aggregates, one can drastically tune assembly pathways, and the resulting thin film morphology and device properties.