Long-term degradation mechanism of tris(8-hydroxyquinoline) aluminum-based organic light-emitting devices

We investigated the cause of the long-term degradation of organic light-emitting devices (OLED) based on tris(8-hydroxyquinoline) aluminum (AlQ3), a widely used electroluminescent small molecule. We found that injection of holes in AlQ3 is the main factor responsible for device degradation. This was verified by constructing devices where predominantly holes were transported through a 5-nm-thick AlQ3 layer. These devices showed a significant decrease in the photoluminescence efficiency upon prolonged current flow, showing that AlQ3 cations are unstable and their degradation products are fluorescence quenchers. This fact naturally explains various approaches, which have been used previously to increase OLED lifetime.