Studies of gate dielectrics in organic field effect transistors (OFETs) have been attractive because the electric properties of OFETs are susceptibly affected by the choice of the gate dielectrics. Here, we demonstrate a tunable threshold voltage in an organic field effect transistor (OFET) using an ion-dispersed gate dielectrics. By applying external electric field (Vex) to the gate dielectrics, the dispersed ions in the gate dielectrics are separated by electrophoresis and form space charge polarization. The drain current of the OFET increased over 1.9 times and the threshold voltage (Vth) decreased 22 V (from -35.1 V to -13.1 V).

The shift direction of Vth was easily tuned by the polarity of the external voltage. The dielectric permittivity of the gate dielectrics and mobility of the active layer were unchanged after the polarization of the gate dielectrics. The UV-VIS differential absorption spectra of the OFETs indicate that there is no chemical doping in the active layer of the OFETs. These results indicated the shifts of threshold voltages were originated from the polarization of gate dielectrics.