(604d) Synergistic Effect of Regioregular and Regiorandom Poly(3-hexylthiophene) Blends for Flexible Organic Devices

Side chain engineering has a significant impact on supramolecular assemblies in conjugated polymer systems. The decrease of regioregularity could lead to an improvement of material mechanical flexibility, which is favorable for the fabrication of flexible organic field effect transistors (OFETs), however, the concomitant decrease in thin-film crystallinity severely deteriorates charge transport performance. Herein, flexible OFETs using regioregular (RR) and regiorandom (RRa) poly(3-hexylthiophene) (P3HT) blend thin-films as the active layer for devices fabricated via solution processing on polyethylene terephthalate (PET) substrates process was demonstrated. In contrast to devices using single component RR-P3HT, the blend thin-films can preserve the prominent charge carrier mobility at 0.1 cm² V^-1 s^-1 with negligible hysteresis even when the active component comprises a small proportion of the blend. Also, transistor performance does not degrade upon application of an external strain of 3.2% owing to the dispersion of the conductive material into the flexible insulating RRa-P3HT matrix. Because a large fraction of oxygen sensitive RR-P3HT was substituted with the inert RRa-P3HT, unintentional p-type doing effects were minimized, resulting in decreased off-current. The blend thin films also facilitate identification of an orthogonal solvent for subsequent dielectric deposition, thus enabling a top gate-bottom contact configuration, which is favorable for ambient stability: the top gate architecture allows the dielectric to serve as an encapsulation layer to protect the underlying semiconductor from atmospheric oxygen and moisture. The fabrication of flexible OFETs required no surface treatment or annealing steps, and processing was conducted under ambient conditions, suggesting a promising method that can meet the manufacturing requirements for roll-to-roll large scale production.