Organic light emitting devices/diodes (OLEDs) are light emitting devices are often made from electroluminescent polymers and small-molecule structures, for example. These devices have received a great deal of attention as alternatives to conventional light sources in displays as well as other applications. In particular, an OLED may an alternative to liquid crystal (LC) materials and structures in displays, because the LC materials and structures tend to be more complicated in form and more limited in application.
OLED-based displays do not require a light source (backlight) as needed in LC displays. OLEDs are a self-contained light source, and as such are much more compact while remaining visible under a wider range of conditions. Moreover, unlike LC displays which rely on a fixed. cell gap, OLED-based displays can be flexible.
While OLEDs provide a light source for display and other applications with at least the benefits referenced above, there are certain considerations and limitations that can reduce their practical implementation. One issue to be considered when using OLED materials is their susceptibility to environmental contamination. In particular, exposure of an OLED display to water vapor or oxygen can be deleterious to the organic material and the structural components of the OLED. As to the former, the exposure to water vapor and oxygen can reduce the light emitting capability of the organic electroluminescent material itself. As to the latter, for example, exposure of the reactive metal cathode commonly used in OLED displays to these contaminants can over time result in ‘dark-spot’ areas and reduce the useful life of the OLED device. Accordingly, it is beneficial to protect OLED displays and their constituent components and materials from exposure to environmental contaminants such as water vapor and oxygen.
In order to minimize environmental contamination, OLED displays are commonly fabricated on thick, rigid glass substrates, with a glass or metal cover sealed at the edges. However it is often desirable to provide the OLEDs on a lightweight flexible substrate. For example, it would be beneficial to use thin plastic (e.g. polymer) substrates in this manner. Unfortunately plastic substrates, such as polycarbonate, are unacceptably susceptible to water vapor and oxygen permeation. While the use of inorganic layers such as SiOx, SiNx and Al2O3 has been investigated as transparent barrier layers to moisture and oxygen, the layers formed of these materials are typically brittle, and thus not useful in flexible substrate applications. Other proposed barrier layers include multi-layer structures, which are rather complex and can also be brittle.
What is needed therefore is a barrier structure that overcomes at least the shortcomings described above.