Role of oxygen-bonds in the degradation process of phosphorescent organic light emitting diodes

For improving the lifetime of organic light emitting diodes (OLEDs), it is essential to understand the chemical reaction pathways involved in the degradation process of these devices. Using the laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS) technique, an OLED based on the phosphorescent emitter tris(phenylpyridine)iridium (Ir(ppy)3) was investigated. We show that the chemical dissociation reaction of the Ir(ppy)3 molecule and an additional complexation of its fragments with the used hole blocking material 4,7-diphenyl-1,10-phenanthroline is the main intrinsic degradation mechanism. This finding underlines the exciton induced dissociation mechanism of phosphorescent emitters, even at emitters without any metal-oxygen-bonds in the ligand system.