Photoinduced doping of organic field effect transistors studied by displacement current measurement and infrared absorption spectroscopy in multiple internal reflection geometry

In order to investigate a doping mechanism in organic semiconductors, we have studied the influence of oxygen exposure on pentacene and poly(3-hexylthiophene) (P3HT) field effect transistor (FET) using displacement current measurement (DCM). The DCM results revealed that the oxygen doping effect is small in the dark condition, but is much enhanced by light illumination (photoinduced doping). From the result of infrared reflection absorption in the multiple internal reflection geometry (MIR-IRAS) for P3HT film, we conclude that the charge-transfer reaction between P3HT molecule and O₂ molecules is accelerated by the light illumination.