Photo-response of polymer thin-film transistors based on poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene)

Polymer thin-film transistors (PTFT) and resistors based on poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) are fabricated by spin-coating process, and photo-sensing characteristics of the devices are investigated in visible light. Upon illumination, a significant increase in the drain current of the PTFT is observed with a maximum photosensitivity of 198 in the subthreshold operation mode at an illumination intensity of 1200 lux. On the other hand, the photosensitivity of the thin-film resistor is only 18.5 under the same illumination intensity for an applied voltage of 2 V, indicating that there is a photocurrent amplification effect in the PTFT. It is found that the illumination effectively decreases the threshold voltage of the PTFT, but hardly affects its field-effect mobility. The mechanisms for the photocurrent formation in the thin-film resistor and for the photocurrent amplification in the PTFT are discussed.