Effects of Localized Heating at Heterointerfaces on the Reliability of Organic Light-Emitting Diodes

Continuous-wave and pulsed-current stressing was conducted to evaluate the reliability of green phosphorescent organic light-emitting diodes (OLEDs). Through modifications of the ITO anode by different pretreatments and the hole transport layer (HTL) by incorporating inorganic component or dopants, we proved that the energy level misalignment at the ITO/HTL interface leads to localized Joule heating, accelerating material deterioration, and luminescence decay. Stressing with short current pulses was employed to suppress the heating effect. For OLEDs with a large interfacial barrier of 1.2 eV, the effective half life was increased by 70% under pulsed operation, whereas in OLEDs with an interfacial barrier of 0.5 eV, only 14% improvement was obtained, indicating a minor heating role.