Single-layer devices

Fig. 7. Schematic of light emitting diodes (a) single-layer device (b) single heteiostmctuie (c) double heteiostmctuie.

The efficiency of PPV may also be raised by introducing disorder into the polymer chains. The crystallinity of PPV may be lowered by employing a modified Wessling method utilizing a xanthate leaving group 63J. PPV produced by this method is believed to contain a mixture of cis- and rram-alkenc units. The efficiency of the material is 0.22% when employed in a single layer device with... 

The electroluminescence spectra of the single-layer devices are depicted in Figure 16-40. For all these OPV5s, EL spectra coincided with the solid-state photoluminescence spectra, indicating that the same excited states are involved in both PL and EL. The broad luminescence spectrum for Ooct-OPV5-CN" is attributed to excimer emission (Section 16.3.1.4). 

For the same the single layer devices based on Alq3, Peyghambarian et al. [83] found that the 1/V characteristics can also be described by an SCL current flow in the low cu ire lit regime. However, in the low current regime the 1/V characteristics can be qualitatively modeled by the Fowler-Nordheim equation (even if, quantitatively, the real device current differs from the calculated by seven orders of magnitude) [83] and thermionic emission ]78]. 

Figure 13-1. Encigy level diagrams under forward bias, (a) Single-layer device Iransports both holes and clccu ons and emits (b) iwo-layer device with hole and electron transport layers, one or both of which may emit (c) three-layer device with emitting dye doped (here) into a thin region of the electron transport layer.

Light-Emitting Diodes 16.4.2.1 Single-Layer Devices... 

PLED, which resulted in a fivefold enhancement in brightness compared to single-layer devices, with EQEs of —0.01 to 0.11% [149],... 

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