Templating and charge injection from copper electrodes into solution-processed organic field-effect transistors

Solution-processed organic field-effect transistors (OFETs) using chemically modified copper electrodes are reported. The purpose of this study is to shed light on the use of inexpensive copper electrodes in bottom-contact OFETs, which is consistent with the major goal of organic electronics: the realization of low-cost electronics. 6,13-Bis(triisopropylsilylethynyl)pentacene was used for solution-processed hole-transporting molecular films and pentafluorobenzenethiol was used to form self-assembled monolayers (SAMs) on the contact metals. We conducted a comparative study on copper and gold contacts and realized that, under the same performance improvement schemes, via SAM treatment and controlled crystal growth, the copper electrode device experienced a more significant enhancement than the gold electrode device. We attribute the beneficial effects of SAMs to the improved charge injection and transport properties, which are critical double effects from the fluorinated aromatic SAM structure. Grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements showed that templating property of SAMs promotes the crystallization of TIPS-pentacene films at the metal/organic interface. The presented result indicates that copper can be regarded as a promising candidate for reducing the use of gold in organic-based circuits and systems, where the cost-effective production is an important issue.