Degradation in iTMC OLEDs
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1029-F03-30
Degradation in iTMC OLEDs Leonard J. Soltzberg1, Velda Goldberg2, Michael D. Kaplan2, Heather Bankowski2, Shannon Browne2, Heather Concannon1, Megan Damour1, Samantha Green1, Elthea Hendrickson1, HengLian Huang1, Virginia Liu1, Lindsey Piirainen1, Suwathna Reel2, George G. Malliaras3, Jason D. Slinker3, and Stefan Bernhard4 1 Department of Chemistry, Simmons College, 300 The Fenway, Boston, MA, 02115 2 Department of Physics, Simmons College, 300 The Fenway, Boston, MA, 02115 3 Materials Science & Engineering, Cornell University, Bard Hall, Ithaca, NY, 14853-1301 4 Department of Chemistry, Princeton University, Frick Laboratory, Princeton, NJ, 08544 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 [1]. Water has been implicated in this degradation process [2]. We report recent studies on degradation of OLEDs fabricated with Ir(ppy)2(dtb-bpy)PF6 [ppy = 2-phenylpyridine, dtb-bpy = 4,4’-di-tert-butyl 2,2’bipyridine [3]. 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 Ir(ppy)2(dtb-bpy)PF6 systems, seen both in the solid state and in solution samples, may also be indicative of decomposition.
INTRODUCTION OLED devices based on ionic transition metal complexes have several unusual and attractive characteristics, including high brightness and simplicity of construction. However, like other electroluminescent organic substances, these compounds degrade under electrical drive to an extent that limits their utility for most applications. It is likely that different degradation mechanisms are at work in different OLED materials, as suggested by the present results. We have compared iTMC OLED devices made with Ru(bpy)3(PF6)2 and Ir(ppy)2(dtb-bpy)PF6 as the emissive layer, using a variety of physical and chemical methods. We have observed a number of suggestive phenomena that collectively point to differences in the degradation mechanism in these two materials.
EXPERIMENT Device preparation and performance Ir(ppy)2(dtb-bpy)PF6 was synthesized as previously described [3]. Devices were fabricated using commercially prepared glass substrates coated with a patterned strip (25 mm x 3 mm) of ITO for the anode. The iridium complex was dissolved in acetonitrile (24 mg/ml) and layer of the complex was spincoated onto the ITO layer. After annealing the slide overnight at 83oC, four separate aluminum cathodes (3 mm x 1 mm) were vacuum evaporated through a mask onto the organic layer in order to pr
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