Novel LED Structures

The LEDs discussed so far have all been simple planar structures, typically on glass substrates. The unique processing advantages of conjugated polymers also allow a range of novel device structures to be considered, some of which are discussed here. 

The flexibility and low-temperature processing of polymers allow them to be deposited onto plastic substrates. This fact was exploited by Gustafsson et al., who 

Transparent electrodes also allow the fabrication of stacked LEDs with electrodes within the device structure. By applying voltages between different adjacent pairs of electrodes, it is possible to control the amount of emission from each layer and hence to control the color of the emission (see Fig. 5.22), taking advantage of the fact that blue emitters, for example, are transparent to red, green and blue emission. This strategy was first demonstrated in polymer LEDs by Martens et al.,99 and has also been used in molecular organic LEDs.100 

To generate useful display devices from polymer LEDs requires lateral definition of the emissive areas. Simple arrays can be generated by patterning top and bottom 

---