ORGN 95 |
| Even though it is difficult to underestimate the importance of the operational lifetime of organic light emitting diodes (OLEDs) in commercial applications, little is known about the nature of chemical reactions associated with efficiency losses during operation. To gain insight into the chemical mechanism of operational degradation, we studied changes in chemical compositions of fluorescent and phosphorescent OLEDs utilizing carbazole derivatives in emissive layer during operation. We detected substantial losses of emissive components – carbazole-derived hosts – and, if present, phosphorescent dopants. Qualitatively similar to luminance efficiency loss, the extent of chemical transformation was monotonically, yet nonlinearly, related to operational time and current density. Several new materials were found in degraded OLEDs, and some of them were isolated and identified by NMR and MS. Structures of degradation products led to the conclusion that the key step in degradation is homolytic scission of weak bonds in excited state, followed by free radical reactions. |
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Materials, Devices, and Switches
1:00 PM-5:00 PM, Sunday, 10 September 2006 Moscone Center -- Room 132, Oral
Division of Organic Chemistry |