Importance of domain purity in semi‐conducting polymer/insulating polymer blends transistors

Printed electronics is a rapidly developing field of research which covers any electronic devices or circuits that can be processed using direct printing techniques. Among those printing techniques, inkjet printing is a technique of increasing interest for organic field‐effect transistors (FETs) due to its fully data driven and direct patterning. In this work, the morphology of semi‐conducting polymer/insulating polymer blends from inkjet printing and their FET properties have been investigated. We attempted to optimize the morphology of the blends by the addition of a co‐solvent to the blend solution prior to film deposition. By varying the boiling temperature of the co‐solvent, blend films are fabricated with varying domain purity and different degree of semi‐conducting polymer ordering. The morphologies of all the as‐cast samples from inkjet printing and subsequently thermally annealed samples are characterized by grazing incidence wide angle x‐ray scattering and small angle neutron scattering. The results indicate that the sample where a low boiling temperature co‐solvent is used exhibits a lower degree of semi‐conducting polymer ordering and less pure domains, resulting in a decrease of hole mobility. The morphologies that are formed when high boiling temperature co‐solvent is used, however, give a higher degree of semi‐conducting polymer ordering along with higher domain purity, significantly improving hole mobility up to 1.44 cm² V^?1 s^?1 at V_DS = 40 V. More importantly, with thermal annealing, all the samples exhibit similar semi‐conducting polymer ordering and domain sizes while the domain purity significantly varies. This work is a unique example that demonstrates the importance of domain purity in the optimization of morphology and FET performance, which is previous unavailable. It also provides a novel process that can efficiently control the morphology of semi‐conducting polymer/insulating polymer mixtures during deposition to maximize FET performance from inkjet printing. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1760–1766