Mechanism of the intrinsic (long-term) degradation in AlQ3-based organic light emitting devices

The intrinsic degradation of hydroxyquinoline aluminum (AlQ(3))-based organic light emitting devices, that leads to the long-term decrease in the electroluminescence efficiency of the devices operated under constant current conditions, has been studied. The role of stabilizing agents, such as introducing a copper phthalocyanine buffer layer at the hole injection contact, doping of the hole transport layer, and using mixed layers of hole and electron transport materials has been investigated. Devices, which allow predominantly holes to be transported through the AlQ(3) layer, showed significant decrease in photoluminescence after prolonged current flow. These results lead to the conclusion that the degradation of AlQ(3) cations is the major cause of intrinsic long-term device degradation. This mechanism also explains some new results on the degradation of devices containing dual layer and doped hole transport layers as well as the increase in lifetime of devices containing more efficient electron injecting contacts.