Organic light emitting diodes – OLEDs

Organic light emitting diodes are light sources, which are used for lighting and displays. OLED displays (also called AM-OLED displays, which is short for active matrix OLED) for mobile devices are currently the most technologically advanced application of organic electronics.
Regarding basic functional principle, OLEDs are similar to organic solar cells. While in solar cells light is transformed into electricity, OLEDs transform electricity into light. Physically speaking this is the same process running in opposite direction.

Consequently a component design similar to that of a solar cell can be used for the OLED. The used materials though are optimized for a different target. While a solar cell should absorb (catch) as much sunlight as possible, the LED should emit as much light of any chosen color as possible. Here, too, organic dyes are employed, but only those which exhibit a particular form of coloring: fluorescence or phosphorescence. This means that the dyes not only absorb light of a particular color, but that they also emit light of a different color at the same time. This can be achieved by illuminating the dye with white, blue or UV light (just like, for example, in the fluorescent dye in a text marker or in the case of a white t-shirt under dark light in a club). This illumination causes the dye to glow and it emits light in a color specific to itself (e.g. yellow, orange or green for text markers). This light emission is called luminescence.
Luminescence cannot only be caused by illumination, but also through a suitable supply of electricity – in this case we have a light source which can be powered by electrical current as usual. The functional principle of this so-called electroluminescence is described on the following pages.


2012 by OES, Johannes Widmer