Organic light-emitting transistors with overlapping gate structure: towards high efficiency at high current density

초록

Organic light-emitting transistors (OLETs) combining the dual functions of electrical switching and light emission are promising devices to push large amounts of charge carriers into an isolated recombination area. Most OLETs proposed so far, however, suffer from hole-electron current imbalance when driven at high currents. This results in a light emission zone very close to one of electrodes. The proximity of the electrode is detrimental to efficient light emission as the metal significantly quenches excitons. In addition, in single gate OLETs, the emission zone can unpredictably switch from one contact to the other upon small bias changes since electron and hole currents are not controlled individually. Here, we introduce the overlapping-gate OLET without the horizontal gap between the two gates in the center of the channel. In this topology, each gate is independently used to accumulate one type of charge carrier, opening a unipolar channel to transport and inject charge into the recombination zone. For the active layer, we propose a multi-layered structure of organic semiconductors, using high mobility p- and n-type materials for efficient lateral transport and a fluorescent emissive layer for the recombination zone. The OLET combines current balance up to high current levels and a recombination zone isolated from the quenching electrodes. As a result, high performance red-emitting OLETs are demonstrated with an external quantum efficiency of 5.6% at a high luminance over 2000 cd m?2. The effects of gate biases on charge balance and exciton confinement in the center of the transistor channel are further discussed.