Organic polymer thin film phototransistors

Abstract

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.