We present results on the electrical characterization of gate-planarized organic polymer thin-film transistors (OP-TFTs). We investigated the time dependence of the OP-TFT current. Over a relatively short time range (several 100ms), we observed a decrease of the OP-TFT current corresponding to the establishment of the steady-state regime, and is slower when the transistor is in the weak accumulation regime or in the OFF-state. We believe that this is associated with carrier thermalization in the organic semiconductor. Over longer time scales, the decrease of the OP-TFT current is due
to device aging and can be associated with a threshold voltage shift, up to 20V after an electrical stress at VGS=-30V for 30min at room temperature. This shift is fully reversible once the gate polarization is removed and might be associated with charge trapping in the semiconductor.
We have investigated the effects of illumination, both broadband and monochromatic, on the electrical performance of organic polymer thin-film transistors (OP-TFTs). In each case, providing the illumination is sufficiently absorbed by the organic polymer, the drain current of a device biased in the OFF-state is significantly increased. We have observed increases in the OFF-state drain current as large as several orders of magnitude depending on the intensity of the incident
illumination. Whereas, the drain current of a device biased in the strong accumulation regime is relatively unaffected by the incident illumination. The illumination also serves to decrease the threshold voltage and increase the subthreshold slope, but has little effect on the field-effect mobility of the charge carriers. We explain these effects in terms of the photo-carrier generation in the channel region of the device due to the incident illumination. We have also studied how our OP-TFTs respond to the turn-on and turn-off of gate bias under illumination and to the turn-on and turn-off of
illumination at certain gate biases.