Electrical Properties of Trilayer Organic Light-Emitting Diodes With a Mixed Emitting Layer

We investigate the electrical properties of three different trilayer organic light-emitting diodes (OLEDs), one of which is based on a conventional layered structure and the others on a blended structure where an emitting layer (EML) is uniformly or stepwise mixed with an electron transport layer (ETL), Tris-(8-hydroxyquinoline) aluminum ( Alq₃). By way of simulations, we visualize the electrical behaviors that provide a clear understanding on why the uniformly mixed structure enhances further the longevity of OLEDs, compared to the other configurations. Namely, the uniformly mixed structure has the lowest concentration of positive charges in the ETL (thereby reducing oxidative degradation of Alq₃) and weakest electric field (decreasing the probability of Joule heating), followed by the stepwise mixed one and then the layered one. However, such blended structures show lower recombination efficiency due to the delocalization of carriers (recombination), which has been demonstrated by simulations of the current balance.