Degradation of Ir(ppy)_2(dtb-bpy)PF_6 iTMC OLEDs

摘要

Simplicity of construction and operation are advantages of iTMC (ionic transition metal complex) OLEDs (organic light emitting diodes) compared with multi-layer OLED devices. Unfortunately, lifetimes do not compare favorably with the best multi-layer devices. We have previously shown for Ru(bpy)_3(PF_6)_2 based iTMC OLEDs that electrical drive produces emission-quenching dimers of the active species. We report evidence here that a chemical process may also be implicated in degradation of devices based on Ir(ppy)_2(dtb-bpy)PF_6 albeit by a very different mechanism. It appears that degradation of operating devices made with this Ir-based complex is related to current-induced heating of the organic layer, resulting in loss of the dtb-bpy ligand. (The dtb-bpy ligand is labile compared with the cyclometallated ppy ligands.) Morphological changes observed in electrically driven Ir(ppy)_2(dtb-bpy)PF_6 OLEDs provide evidence of substantial heating during device operation. Evidence from UV-vis spectra in the presence of an electric field as well as MALDI-TOF mass spectra of the OLED materials before and after electrical drive add support for this model of the degradation process.