“Electroluminescent optoelectronic devices”
Iulia Corina CIOBOTARU, Constantin Claudiu CIOBOTARU, Silviu Pavel POLOSAN*
Optoelectronic devices based on electroluminescence are mainly p-i-n heterojunctions, in which the intrinsic layer is provided by the electroactive OLED layer, which consists of organometallic compounds embedded in conducting, transparent polymers. Then, the electron and hole transport layers were added, and the sandwich structure was capped with two electrodes: one an anode of an oxidic compound (indium tin oxide) and the other, a cathode of a noble metal (Al, Au, Ag).
The main OLED functional parameters can be extracted, including current density, current efficiency, electroluminescence (compared with photoluminescence), and external quantum efficiency. For a new synthesized organometallic IrQ(ppy)2, the resulting color of the electroluminescence is orange, but the color changes with the applied voltage, as can be seen in the CIE representation.
From the current–voltage characteristics, the turn-on voltage is around 3 V, which is slightly higher than in other devices. An increase in the IrQ(ppy)2 concentration was necessary to balance the orange color of the electroluminescence.
Electroluminescent materials are not only organometallic compounds but also any compound with a long exciton lifetime. A new class of electroluminescent compounds comprises the perovskite-structured organic-inorganic materials that form self-trapped excitons.