Thermal Gradient Assisted Growth of Morphologically Controlled Crystals from a Mixture of Small-Molecule Organic Semiconductor and Polymer ~Toward Organic Field-Effect Transistor Application~

Organic semiconductors have been widely studied in recent years because of their light-weight, flexibility, and low-end. Soluble materials have been developed to further minimize process costs; among these 6,13-bis(triisopropylsilylethinyl) pentacene (TIPS-pentacene) combines printability, air-stability, and high electrical performances. TIPS-pentacene crystals yielded by simple drop-casting are affected by random orientation, lack of areal coverage, and non-homogeneous film thickness, which lead to poor electrical performances and high device-to-device variability. To reduce morphological issues and therefore increase Organic Field-Effect Transistors (OFETs) performances, in this research, organic films have been yielded by applying two methods; a thermal gradient and blending TIPS-pentacene with a polymeric material (polystyrene). The former method enhances areal coverage and crystal orientation, while the latter one is mainly effective on charge mobility and its consistency. Finally, the thermal gradient has been applied through a mixture of TIPS-pentacene and polystyrene to combine advantages given by the two single methods. Crystal orientation is optimized; however, despite electrical properties attained with pristine TIPS-pentacene have been confirmed, further performance enhancements are prevented by an unexpected lack in crystallinity and a non-homogeneous vertical phase separation between semiconductor and polymer across the whole substrate.