Multilayer device structure

The main starting point for thin-fihn low molecular weight materials was the work reported by Ching W. Tang and Steven van Slyke of Kodak in 1987, when they described the green electrolnminescence obtained from a thin film of vapour deposited aluminium tris(8-hydroxyquinoline) (Alq). ° Since that time the development of multilayer device structures and several new important classes of organic EL materials has led to snbstantial improvements and to the commercial development of display technologies based on this system. ... 

In one recent study, Mn2+-doped CdS nanocrystals grown with a ZnS passivating shell were used as the recombination centers in direct current (dc) electroluminescent devices (104). The Mn2+ CdS/ZnS nanocrystals were prepared by the inverse micelle procedure (102) (see Section II.C) and these colloids were incorporated into a multilayer device structure by spin-coat... 

The first decision in choosing a synthetic method for a PPV material is the way in which the material will be processed (Scheme 7.8). The precursor routes will enable the preparation of solvent-resistant and more durable thin films of PPV. This is particularly desirable if a multilayer device structure is required for the application. When choosing different precursor methods, it is important to assess the criteria of the application. Most precursor methods involve a thermal elimination step to convert the precursor polymer to the PPV material. Sul-fonium precursors require higher-temperature elimination compared to sulfinyl precursors. This makes the sulfinyl route compatible with deposition on plastic substrates. Another factor to consider in precursor methods is the nature of the elimination byproducts. Sulfonium precursors convert to PPV with elimination of acids, such as HCl or HBr, which has been shown to be detrimental to device performance. Xanthate and dithiocarbamate routes involve the elimination of amine and CO2 and CS2, respectively. 

OLED devices are fabricated on a glass, plastic, metal, or ceramic substrate as a multilayer-stacked structure represented in Figure 3.1. 

FIGURE 3.1 Schematic of a multilayer OLED device structure. 

From optical point of view, an OLED structure can be considered as a multilayer thin-film system composed of absorbing and nonabsorbing materials, as shown in Figure 6.27. Therefore, the optical properties and optimal structure of such a multilayer device can be investigated by applying thin-film optical analysis techniques. Based on the theory of optical admittance analysis for analyzing the optical properties of a thin-film system [92], the optical properties of an OLED thin-film system can be simulated to reduce the ambient reflection. 

Other authors have produced multi-ion chemfets. Matsuo and Esashi have demonstrated that multi-ion ehemfet structures can be planar processed in a two-ion needle shaped form (48). Their ingenious needle shaped design permits them to incorporate two or possibly three sensitive elements at the tip. However, the demands of electrical and chemical isolation become increasingly difficult as the number of ion sensitive elements increases in these devices. Pace has demonstrated that a pH sensitive element, combined with a multilayer composite structure, can be used to detect a wide range of chemical species (56). This concept is quite versatile and has been proposed as the means to extend the capability of the pH sensitive... 

The use of insoluble, highly cross-linked anisotropic networks created by the polymerisation of photoreactive monomers, eliminates the problem of crystallisation, at least for organic materials, since polymer networks are macromole-cular structures incapable of crystallising, see Chapter 6. Furthermore, the fabrication of multilayer devices would be facilitated by the use of a cross-linked stable HTL next to the anode on the solid substrate surface, onto which subsequent layers can be deposited by vapour deposition. Multilayer OLEDs are intrinsically more stable than monolayer devices due to a better balance of charge-carriers and concentration of the charged species away from the electrodes. The synthesis and cross-linking of a suitable aromatic triarylamine derivative with a polymerisable oxetane group at each end of the molecule for use as a HTL has been reported recently, ... 

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