Investigations of Operational Lifetime and Modes of Failure of Organic Light Emitting Devices

摘要

Reliability limitations of organic light emitting devices (OLEDs) were explored in a joint effort project lead by Princeton University, with subcontracting efforts by the University of Southern California, the University of Texas and Universal Display Corporation. Methodologies and protocols for screening of device structures and materials were developed. Extended lifetimes of red, green and blue phosphorescent OLEDs were achieved. For example, lifetimes of over 50,000 hours were obtained for both red and green devices. Blue device lifetimes observed were still less than 1000 hours. This difference in blue lifetime was studied using through both photo- and electro-luminescence methods, and was determined to be due, in part, to the high energies needed to excite the blue lumophores, which results in charge imbalance in the emission layers of the OLEDs. Contact degradation was also studied at the microscopic scale using near-field scanning optical microscopy (NSOM) in concert with our transparent OLED structure (TOLED). It was found that defects introduced during processing are largely responsible for the formation and growth of dark spots.