(135a) Inducing Molecular Ordering of Polymer Semiconductors in a Secondary Insulating Polymer Matrix to Enable Efficient Charge Transport

Polymer semiconductors (PSCs) are lightweight, mechanically compliant, easily tunable through chemical synthesis, and capable of being deposited over large area, making them excellent candidates for inexpensive printable electronics with functionalities currently underserved by conventional inorganic semiconductors. However, the conformational complexity associated with macromolecules, as well the presence of unique inter- and intra-chain interactions, make it challenging to control the morphology of PSCs in the thin film state. Previously, it has been reported that beyond a certain molecular weight, thin film charge carrier mobility drops due to reduced crystallinity and increased entanglement. We present, the use of an insulating secondary matrix polymer, polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS), to induce molecular ordering of PSCs across multiple length scales. From the molecular level to the device scale, we systematically investigate and elucidate morphological factors associated with improved charge transport in field effect transistors (FETs) fabricated using PSC/insulator blends as the semiconducting layer. Insulator-induced molecular ordering in SEBS/PSC hybrid films is strongly correlated to the molecular weight of the semiconducting component. When a PSC of sufficiently high molecular weight is used, induced molecular ordering leads to a 5-fold increase of charge carrier mobility in field-effect transistors whose active layer contains only 30 wt% of the PSC in SEBS. Moreover, mobility can be further elevated using an extensional-flow driven solution shearing deposition method. These findings show that using a secondary polymer matrix to dramatically improve the molecular organization and charge transport of a high molecular weight PSC is a useful morphological control strategy. It can also be carried out using non-halogenated solvents, such as p-xylene, which are more environmentally benign and industrially relevant than commonly used chlorinated solvents.