Observation of carrier behavior in organic field-effect transistors with electroluminescence under AC electric field

The carrier behavior in a tetracene thin film under AC electric field was examined by electroluminescence (EL) using the structure of organic field-effect transistors (OFETs). A square wave voltage was applied to the source electrode, whereas the drain and gate electrodes were connected to the ground. Electrons and holes were injected from the Au source electrode alternately, and they recombined at the interface between the tetracene thin film and the source electrode. A series of EL pulses was observed in accordance with the applied AC voltage, i.e., a transient EL was observed in a half cycle of AC. This result indicates that alternating carrier injection causes EL. Furthermore, EL intensity increased with the frequency and amplitude of AC voltage. It was suggested that the amount of electrons and holes injected from the source electrode in a unit time is controlled by the frequency and amplitude of AC voltage.