In situ characterization of the oxidative degradation of a polymeric light emitting device

Abstract

Light-emitting devices with polymeric emissive layers have great promise for the production of large-area, lightweight, flexible color displays, but short lifetimes currently limit applications. We address mechanisms of bulk polymer degradation in these devices and show through in situ Fourier transform infrared characterization of working light-emitting devices with active layers of poly[2-methoxy,5-(2′-ethyl-hexoxy)-1,4-phenylene vinylene] that oxygen is responsible for the degradation of the polymer film. A mechanism is given based on the formation of singlet oxygen from oxygen impurities in the film via energy transfer from a nonradiative exciton. Fourier transform infrared and x-ray photoelectron spectroscopy results are consistent with the mechanism, involving singlet oxygen attack followed by free radical processes. We further show that oxygen readily diffuses into the active polymer layer, changing the electrical characteristics of the film even at low concentrations. Thus, polyphenylene-vinylene-based light-emitting devices will self-destruct during operation if fabricated without special attention to eliminating oxygen contamination during fabrication and device operation.

Boron clusters: Do they receive the deserved interest?

“…These differentiating results suggest that they must be due, in great part, to the nonnucleophilic anion in the polymer. We observe, then, that not all clusters produce a high overoxidation resistance, and that the dianionic cluster [B 10 Cl 10 ] 2-produces PPy[B 10 Cl 10 ] with an overoxidation resistance similar to those measured for materials doped with common anions. We have presented this example to show one particular case where the cluster nature of the anion, the delocalization of its charge and their "three-dimensional aromaticity" can make these borane anions very relevant.…”

“…However, a major obstacle to their commercialization is the relatively poor stability of the conducting polymer-based devices [7] which present several degradation mechanisms. One is associated with rapid oxidation by water or oxygen [8][9][10]. The conducting phase can be made insulating by applying a reducing potential.…”

Kinetic studies of the photo-degradation of poly(arylene vinylenes)

“…Also the production of singlet oxygen was confirmed by its phosphorescence [12] and by electron spin resonance spectroscopy (ESR) spin tap experiments [4]. Other studies of the degradation process yielded spectroscopic evidence that carbonyl groups such as aldehydes were produced during the process [13,14].…”

Organic semiconductors for device applications: current trends and future prospects

“…OS are generally sensitive to moisture and oxygen and therefore need encapsulation for proper protection [704][705][706] from further deterioration during their use in devices. Consequently, device reliability issues arise due to the environmental instability of both the active materials and low work function electrodes.…”