Inducing Molecular Aggregation of Polymer Semiconductors in a Secondary Insulating Polymer Matrix to Enhance Charge Transport

Polymer semiconductors (PSCs) are a desirable class of materials for next-generation electronics. However, the conformational complexity associated with macromolecules, as well as the presence of unique inter- and intrachain interactions, make it challenging to control the morphology of PSCs. Previously, it has been reported that beyond a certain molecular weight, thin-film charge carrier mobility typically drops due to reduced crystallinity and increased entanglement. Here, the use of an insulating secondary matrix polymer, polystyrene-block-poly(ethylene-ranbutylene)-block-polystyrene (SEBS), is shown to induce molecular ordering of PSCs across multiple length scales. Aggregation-induced molecular ordering in SEBS/PSC hybrid films is strongly correlated to the molecular weight of the semiconducting component. The higher the molecular weight of PSC used to blend with SEBS, the greater the observed improvement in polymer aggregation and orientation. This leads to a 5-fold increase of charge carrier mobility, from 0.3 to 1.5 cm(2) V(-1)s(-1) (P-97k), in field-effect transistors (FETs) with only 30 wt % of the semiconducting polymer in SEBS. Moreover, mobility can be further elevated to 2 cm(2) V(-1)s(-1) using an extensional flow-driven solution shearing deposition method. The findings here on using a secondary polymer matrix to dramatically improve the molecular organization and charge transport of a high-molecular-weight PSC are a useful morphological control strategy. It can also be carried out using nonhalogenated solvents, such as p-xylene, which are more environmentally benign and industrially relevant than commonly used chlorinated solvents.