Tuning of threshold voltage in organic field-effect transistor by dipole monolayer

We have studied the threshold voltage shift of top-contact organic field-effect transistors (OFETs) with a dipole monolayer between pentacene active layer and SiO₂ gate insulator. Since dipole moment projection in normal of the monolayer can be regulated by changing the ordering, the relationship between threshold voltage shift and spontaneous polarization of the monolayer has been gained. Experimental results show the dipole monolayer causes a large negative threshold voltage shift and the shift is linearly proportional to the polarization of the monolayer. We propose a dipole layer model to interpret the observed phenomena with an assumption that the threshold voltage shift is due to compensation of electric field in organic semiconductor layer induced by the dipole monolayer, which is uncommon for the general consideration. Excitingly, a good agreement between the experiment and the analysis shows validity of our modeling and provides the capability of tuning threshold voltage for OFET devices.