Operating longevity of organic light-emitting diodes with perylene derivatives as aggregating light-emitting-layer additives: Expansion of the emission zone

We describe aggregating perylene derivatives as light-emitting-layer (LEL) additives in organic light-emitting diodes (OLEDs). These molecules readily form emissive aggregates when added to the LEL. In the resulting devices, the aggregates show moderate external quantum efficiencies of 0.9%-1.7%, which can be improved to 2.7%-4.0% by further adding a proper dopant. Importantly, addition of these polycyclic aromatic hydrocarbons increases the half-life (t(50)) of undoped and doped OLEDs by 30-150 times. Thus, 11 cd/A green and 5.2 cd/A red devices are produced that have pure color, Commission Internationale de l'Eclairage 1931 2 degrees color chromaticity coordinates (CIEx,y) 0.32, 0.63 and 0.64, 0.36, respectively, and t(50) of 30 000 and 200 000 h, respectively, upon operation at 40 mA/cm(2). A possible link between the thickness of the emission zone and the lifetime increase is illustrated by comparing aluminum 8-hydroxyquinoline chelate (Alq(3)) as an LEL host versus an Alq(3)+dibenzo[b,k]perylene mixed host using C545T as an emissive probe. The comparison suggests that the emission zone and probably the electron-hole recombination zone are expanded for the mixed host. (c) 2006 American Institute of Physics.