Applications of Organic and Printed Electronics by Eugenio Cantatore

Author:Eugenio Cantatore
Language: eng
Format: epub
Publisher: Springer US, Boston, MA

The relatively broad emission spectra from organic materials make it possible that white OLEDs containing three emitting layers can have a very high Color Rendering Index (CRI), up to 90 or more. The CRI expresses the degree to which emission colors of all wavelengths in the visible range are present, which determines the naturalness and vividness of the colors reflected from illuminated objects, i.e. the “pleasantness” of the light source. It is a number in between 0 (bad) and 100 (excellent).

Whereas to-date standard OLEDs are produced by deposition on a thin rigid glass substrate, the small thickness of the active layers and the electrode layers (only a few hundreds of nanometres in total) makes it possible to produce OLEDs which are flexible and even bendable by deposition on e.g. a polymer foil. Figure 4.3 shows an example of such an OLED. This is expected to open up entirely new areas of applications. Additional demonstrated features of white OLEDs are the operation at safe low voltages (close to the thermodynamic limit of approximately 3 V), easy dimmability, the possibility to tune the emission color, and the possibility to create OLEDs which are transparent in the off-state and emissive to both sides in the on-state (using two conductive transparent electrode layers). At present, color-neutral transparencies of approximately 75 % have been demonstrated.

Fig. 4.3Flexible white OLED (Source http://www.holstcentre.com/NewsPress). Photograph reproduced with permission of the Holst Centre (Eindhoven, The Netherlands)

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