Surfaces OLEDs

All substrate preparations prior to the deposition of the organic materials are carried out in a clean room environment to minimize particulates on the anode surface. OLEDs are typically... 

The materials described in the preceding section may be combined in an OLED de vice in a variety of different geometries and compositions. The simplest of these is a single oiganic layer sandwiched between two electrodes. In contrast to the convention used in surface science, it is customary to list the layers in the order of deposition. Thus, anode/organic/cathodc (for example, ITO/PPV/A1) implies that the anode (ITO) is deposited first on the (presumably transparent) substrate. 

Other materials such as gold (< = 4.9 eV), aluminum (< = 4.2 eV), indium-doped zinc oxide, magnesium indium oxide, nickel tungsten oxide, or other transparent conductive oxide materials, have been studied as anodes in OLEDs. Furthermore, the WF of ITO can be varied by surface treatments such as application of a very thin layer of Au, Pt, Pd, or C, acid or base treatments, self-assembly of active surface molecules, or plasma treatment. 

Although even lower WF can be achieved with, e.g., Yb (0 = 2.4 eV), the low reflectivity index of the latter makes it less suitable for OLED applications. The active metal Ca (0 = 2.60 eV) often has to be accompanied with other metals such as Al to increase the device lifetime. It is worth noting that the WF of the metals can be affected by their purity, their deposition method, and the surface structure, and the crystal orientation of the deposited films. 

The performance of OLED devices employing CuPc as a HIL is unstable due to thermally induced HTM crystallization on the CuPc surface [27]. One approach to improve the hole injection and enhance the device stability is to overcoat the CuPc or else to directly deposit... 

ANODE MODIFICATION FOR ENHANCING OLED PERFORMANCE 6.2.1 Indium Tin Oxide Surface Treatment and Modification... 

Figure 6.14 illustrates an OLED microcavity structure that comprises a stack of organic layers for providing EL, an upper electrode, and a bottom bilayer electrode of metal transparent conductive layer. The thickness of the transparent conductive layer (e.g., ITO) in the OLED structures can be varied across the substrate surface so as to achieve color tuning. One typical structure of the devices is glass/Ag/ITO (with a graded film... 

The morphology of the organic films can be assessed using optical microscopy (in particular techniques such as Nomarski microscopy, atomic force microscopy, and surface profiling techniques). It should also be noted that the purity of the organic materials used is of crucial importance for efficient charge transport and emission in addition to the lifetime of the OLED. 

Eischens and Pliskin have interpreted the infrared spectra of ethylene chemisorbed on nickel dispersed on silica 32). When introduced to a surface previously exposed to hydrogen, ethylene gave rise to absorption bands which correspond to the C—H stretching frequencies of a saturated hydrocarbon (3.4-3.5 p) and a deformation associated with a methylene group (6.9 p). A weak band at 3.3 p was attributed to an ole-finic C—H. Treatment of the chemisorbed ethylene with hydrogen caused the spectrum to change to one which was interpreted as due to an adsorbed ethyl radical. Apparently in the presence of hydrogen most of... 

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