Inkjet-printed organic thin film transistors based on TIPS pentacene with insulating polymers

Abstract

The blending of the crystalline organic semiconductor, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene), with amorphous polymers exhibits not only excellent solution processability, but also superior performance characteristics in organic thin film transistors (OTFTs). To understand the inkjet-printing behavior of TIPS pentacene/polymer blends, we use amorphous polycarbonate (APC), which is structurally beneficial to the facile phase separation of TIPS pentacene crystals due to the strong segregation strength estimated by the Flory–Huggins interaction parameter. The various inkjet-printing behaviors of TIPS pentacene/APC inks, which depend on the TIPS pentacene/APC compositions, ink viscosities, and different solvent mixtures, are investigated. These behaviors can ultimately determine the phase separation, morphology, shape, and orientation of the TIPS pentacene crystals in OTFT films. Flory–Huggins phase separation theory is applied, and various analytical methods, such as polarized optical microscopy, 3D surface profile, and time-of-flight secondary ion mass spectroscopy (TOF-SIMS), are utilized to explain these relationships. By controlling these inkjet-printing conditions, it is possible to easily regulate the optimal inkjet-printing process for TIPS-pentacene/polymer systems, which can derive the desirable stripe-shaped and vertically phase-separated TIPS pentacene crystals with the proper orientation and enhanced surface morphology. The resultant inkjet-printed films from the TIPS pentacene with APC show excellent device stability and an average mobility of 0.53 cm² V⁻¹ s⁻¹. Furthermore, the inkjet-printed flexible OTFT array with an average mobility of 0.27 cm² V⁻¹ s⁻¹ sustains the application of TIPS pentacene/APC in the field of flexible printed electronics.