Degradation in 1TMC OLEDs

Abstract

The processes underlying degradation of organic light emitting diodes (OLEDs) are gradually becoming understood. In ruthenium-based ionic transition metal complex (iTMC) OLEDs, a dimeric species forms during device operation that quenches light emission [11. Water has been implicated in this degradation process [21. We report recent studies on degradation of OLEDs fabricated with fr(ppy)2(dtb-bpy)PF6 [ppy = 2-phenylpyridine, dtb-bpy = 4,4'-di-tert-butyl 2,2'- bipyridine [31. We have found that applying a thicker-than-usual metal electrode results in shorter turn-on times and higher light emission, though little improvement in lifetime. It appears that the degradation of these devices occurs by a different mechanism from that of the ruthenium-based devices and may involve local heating leading to chemical decomposition of the organic material. Observation of recurring but often transient dark-colored substances in both the Ru(bpy)3(PF6)2 and fr(ppy)2(dtb-bpy)PF6 systems, seen both in the solid state and in solution samples, may also be indicative of decomposition. © 2008 Materials Research Society