Chemistry Reference
In-Depth Information
10.5.2 Light-Emitting Diodes (OLEDs)
Normal OLED devices require hole (positive charge) and electron injection
from the anode and cathode, respectively. These charges are passed through the
hole- or electron-transporting layer, leading to the 1:1 coupling in the emitting
layer. If coupling occurred, a singlet exciton, leads to a bright luminescence
from the fluorescent material (Figure 10.17). Occasionally, phosphorescence
would be observed as a result of an intersystem crossing [175]. From a
macroscopic viewpoint, the first requirement is control of injection barrier at
the interface between the electrode and material. Thickness control of the
carrier transport layers is effective to some extent not to induce a significant
voltage drop. In addition, the methodology for tuning of the barrier using an
intermediate layer is well established. However, this strategy requires
very complicated device architecture based on the multilayered processing.
FIGURE 10.17
Potential diagram of an electroluminescence (EL) device before and after
biasing.
