Surface modification with a fluorinated N-heterocyclic carbene on Au: effect on contact resistance in organic field-effect transistors

Providing strong carbon-metal (C-M) bonds, N-heterocyclic carbenes (NHCs) recently were introduced as surface modifiers for various applications. Here we report a fluorinated NHC (F-NHC) monolayer chemically bonded to Au with high thermal stability up to 200 degrees C. The effect of F-NHC modification on contact resistance in organic field-effect transistors (OFETs) was further investigated. In comparison to devices without F-NHC modification, transistors with the F-NHC modified gold electrodes show a significant improvement in carrier mobility in the saturation region owing to the reduced contact resistance (R-c). Density Functional Theory (DFT) calculations indicate that, when bonding to Au, the F-NHC molecule transfers 0.40 e to Au and creates a doping interface between Au and p-type organic semiconductors. The charge transfer between the F-NHC and Au leads to a generation of holes at the F-NHC/organic semiconductor interface, which may cause an efficient carrier tunneling for contact resistance improvement. The work lays the foundation for the future applications of carbenes in organic electronics.