The Origin of Low Contact Resistance in Monolayer Organic Field-Effect Transistors with van der Waals Electrodes

The successful commercialization of organic field-effect transistors (OFETs) for advanced integrated organic electronics requires reducing device sizes, which inevitably clashes with the constraints imposed by the contact effects. Herein, it is demonstrated that the contact resistance in OFETs based on monolayer organic semiconductors is extremely low, especially at mild biasing conditions. The contributions of the access resistance and the metal-organic interface resistance are successfully disentangled for the first time. It is shown that, contrary to the conventional view, the contact resistance of monolayer OFETs in the saturation regime exhibits a very weak dependence on the source electrode length. In the monolayer OFETs based on 2,9-didecyldinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (C₁₀-DNTT), a gate-voltage-independent access resistivity (2.2 × 10^-2 Ω cm²) at V _DS = -1 mV is obtained, while the interfacial metal-organic Schottky contact resistance is found to be negligible. The depletion of a diode associated with the metal-organic interface expands with increasing V _DS and eventually bottlenecks the device performance. Finally, how to overcome such a carrier depletion contact resistance bottleneck and achieve OFETs with outstanding performance are shown. These findings pave the way toward sophisticated organic electronic applications based on the use of monolayer OFETs.