Building blocks for ultrathin flexible organic electroluminescent devices

Displays based on organic electroluminescent (EL) materials have entered the marketplace already and demonstrated remarkable contrast, high brightness and crisp colors. However, one of the key advantages of this new technology has not been commercially exploited yet: Fabrication of a display that is still fully functional even when it is bent or flexed. This is possible since organic EL devices comprising only thin, amorphous solid state films and optical properties have no critical dependence on the film thickness. In this paper we address the important elements that are required to produce a flexible organic EL display. Most crucial is the selection of a flexible substrate. Here we present results obtained with ultra-thin inorganic glass materials as well as polymeric foils. For the glass substrates we determined the ultimate mechanical properties for different device configurations. In the case of polymeric substrates permeation of water and oxygen molecules through the substrate is the governing factor. We compare the performance of different barrier systems. In summary we demonstrate that OLED devices with certain flexibility can be reliably built on ultra-thin glass substrates. For polymeric substrates a lot of progress has been achieved in terms of the required barrier properties and other necessary ingredients and this might result later into a commercial organic EL product.