AC-biased organic light-emitting field-effect transistors from naphthyl end-capped oligothiophenes

The photoluminescence and electroluminescence of two devices made from naphthyl end-capped oligothiophenes are investigated based on an organic light-emitting field-effect transistor (OLEFET) configuration. A novel method to light up an active organic layer using a sinusoidal alternating current (AC) gate voltage is examined. The electroluminescence spectra from both materials are very similar to their photoluminescence spectra indicating that the light emission is caused by the same electronic transitions. The intensity of the electroluminescence emission increases with increasing frequency of the AC gate voltage, and it is non-linearly dependent on the amplitude of the AC gate voltage. Moreover, light emission on both sides of the charge transporting channel is revealed by an optical microscope when the channel is appropriately wide, e.g. 10 μm. A simple model involving sequential injection of both charge-carrier types from one electrode into the organic material explains the results.