Comparing the Gate Dependence of Contact Resistance and Channel Resistance in Organic Field-Effect Transistors for Understanding the Mobility Overestimation Issue

Contact resistance is a common issue in organic field-effect transistors (OFETs). Although it is well known that both the contact resistance (R
_C
) and channel resistance (R
_Ch
) are generally gate-dependent, i.e., the resistance values are reduced by increasing gate voltages, the comparison of the gate dependence of R
_C
and R
_Ch
has rarely been reported. In this letter, we used scanning Kelvin probe microscopy to experimentally measure and compare the gate dependence of the two resistances. The results provide valuable information regarding the charge injection/extraction physics in OFETs. Moreover, the correlation between the gate dependence of the two resistances and the charge transfer characteristic of OFETs was investigated, which can give us some clues to the understanding of the non-ideal transfer curves (“kink” feature) observed in high-mobility OFETs, an issue that has caused both great interest and concern in the community.