Decoupling the Effects of Self-Assembled Monolayers on Gold, Silver, and Copper Organic Transistor Contacts

In bottom-contact organic field-effect transistors (OFETs), the functionalization of source/drain electrodes leads to a tailored surface chemistry for film growth and controlled interface energetics for charge injection. This report describes a comprehensive investigation into separating and correlating the energetic and morphological effects of a self-assembled monolayers (SAMs) treatment on Au, Ag, and Cu electrodes. Fluorinated 5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT) and pentafluorobenzenethiol (PFBT) are employed as a soluble small-molecule semiconductor and a SAM material, respectively. Upon SAM modification, the Cu electrode devices benefit from a particularly dramatic performance improvement, closely approaching the performance of OFETs with PFBT-Au and PFBT-Ag. Ultraviolet photoemission spectroscopy, polarized optical microscopy, grazing-incidence wide-angle X-ray scattering elucidate the metal work function change and templated crystal growth with high crystallinity resulting from SAMs. The transmission-line method separates the channel and contact properties from the measured OFET current-voltage data, which conclusively describes the impact of the SAMs on charge injection and transport behavior.