Degradation of organic light-emitting diodes under different environment at high drive conditions

The origin of dark spots, crucial for understanding the degradation mechanisms in organic light-emitting diodes (OLEDs), is typically attributed to the penetration of moisture, oxygen and other active atmospheric agents. Employing scanning X-ray photoelectron spectromicroscopy we have investigated the morphology and chemical composition of degraded micro-areas created in OLEDs under different environment. The same confined degradation events, involving decomposition of the ITO film and organic layer and oxidation and delamination of the Al cathode were observed even for devices grown in situ and operated in ultra-high vacuum at pressures lower than 10−9 mbar. Our results provide unambiguously prove that ‘uncontrollable’ imperfections in the fabricated structures are the major cause for ignition of degradation events, whereas external causes related to the air ambient act as efficient promoters.