Anomalous hysteresis in organic field-effect transistors with SAM-modified electrodes: Structural switching of SAMs by electric field

Self-assembled monolayers (SAMs) are efficient tuners of metal work functions, and have been widely used to modify source/drain electrodes of organic field-effect transistors (OFETs) to achieve effective charge injection from the electrodes into organic semiconducting layers. The device characteristics of OFETs with Au electrodes modified with 1-alkanethiol SAMs were investigated and displayed an anomalous hysteresis opposite to that generally observed. Measurements of OFETs with different SAM molecular species or different average surface densities indicate that an increase in drain currents by tunnelingbarrier narrowing accompanied by a structural order-disorder switching of the SAMs causes such hysteretic behavior. Furthermore, time evolution measurements of OFET drain currents indicate that an electric field perpendicular to the surface of the SAM-modified electrodes, i.e., a drain voltage, induces the switching. The anomalous hysteresis unveiled in this study is indicative of an electrically-stimulated switching of SAMs, which has many implications with respect to the development of future molecular switches.