Stability characteristics of quinacridone and coumarin molecules as guest dopants in the organic LEDs

During stability testing of organic light-emitting diodes (LEDs), a large amount of current (charge) injected into the LED cells raises the cell temperature quite a bit. The morphology of the organic thin films may have changed and formed the excimer and exciplex between different molecules. To keep the excimer and exciplex from forming during the driving test, the organic molecules should give steric hindrance by bulky substituents so that they do not move in the films. Moreover, the molecular structures should not have reactive chemical bonds. A cell doped with quinazoline or quinacridone, with bulky substituents at the imino group side in the Alq host, has a longer operational half-lifetime than that of a cell with quinacridone doping. A cell doped with coumarin derivative, which has no imino and carbonyl, also has a longer operational half-lifetime than that of a cell doped with coumarin with imino and carbonyl.