  Contact resistances between organic semiconductors and metal electrodes have
been shown to play a dominant role in electronic charge injection properties of
organic field-effect transistors. These effects are more prevalent in short
channel length devices and therefore should not be ignored when examining
intrinsic properties such as the mobility and its dependence on temperature or
gate voltage. Here we outline a general procedure to extract contact
current-voltage characteristics and the true channel mobility from the
transport characteristics in bottom contact poly(3-hexylthiophene) field-effect
transistors, for both Ohmic and nonlinear charge injection, over a broad range
of temperatures and gate voltages. Distinguishing between contact and channel
contributions in bottom contact OFETs is an important step toward improved
understanding and modeling of these devices.
