Contact-Induced Nucleation in High-Performance Bottom-Contact Organic Thin Film Transistors Manufactured by Large-Area Compatible Solution Processing

TLDR: In this paper, the authors investigated contact-induced nucleation in the context of small-molecule OSCs and OSC:polymer blends prepared by blade coating, a printing process capable of mimicking large area batch and roll-to-roll manufacturing.

Abstract: Scalable manufacturing of small-molecule organic thin film transistors (OTFTs) with performance approaching single crystals requires extraordinary control over microstructures and morphologies of organic semiconductors (OSCs). Here, contact-induced nucleation in the context of small-molecule OSCs and OSC:polymer blends prepared by blade coating, a printing process capable of mimicking large area batch and roll-to-roll manufacturing, is investigated. Using polarized optical microscopy, microbeam grazing incidence wide angle X-ray scattering, and energy-filtered transmission electron microscopy, it is revealed that previous design rules drawn from spin coating of OSCs and contact-induced nucleation may have to be revisited in the context of blade coating. It is shown that blade coating achieves texture purity in case of 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT), irrespective of whether the contact is chemically treated with a halogenated self-assembled monolayer (SAM) or not, in contrast to spin coating which requires an SAM. Here, it is demonstrated that OSC–contact interactions increase the nucleation density and can disrupt the vertical stratification in polymer:OSC blends with great detrimental effects on carrier transport. Using these lessons, we demonstrate bottom-contact bottom-gate OTFTs without chemical surface modification achieving hole mobilities of 4.6 and 3.6 cm2 V−1 s−1, using 6,13-bis(triisopropylsilylethynyl)pentacene and diF-TES-ADT, respectively, blended with an insulating polymer.