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Degradation of Ir(ppy)2(dtb-bpy)PF6 iTMC OLEDs

Abstract

Simplicity of construction and operation are advantages of iTMC (ionic transition metal complex) OLEDs 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(PF6)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)PF6 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)PF6 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.

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1 Goldberg, V. Kaplan, M.D. Soltzberg, L.J. Bankowski, H. Browne, S. Concannon, H. Damour, M. Green, S. Hendrickson, E. Huang, H. Liu, V. Piirainen, L. Reel, S. Malliaras, G.G. Slinker, J.D. and Bernhard, S.: Degradation in iTMC OLEDs, in Interfaces in Organic and Molecular Electronics III edited by Kavanagh, Karen L. (Mater. Res. Soc. Symp. Proc. 1029E 1029E, Warrendale, PA, 2007), F3.30.
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Keywords

Degradation of Ir(ppy)2(dtb-bpy)PF6 iTMC OLEDs

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