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OLED principle

In Section 13.2, we introduce the materials used in OLEDs. The most obvious classification of the organic materials used in OLEDs is small molecule versus polymer. This distinction relates more to the processing methods used than to the basic principles of operation of the final device. Small molecule materials are typically coated by thermal evaporation in vacuum, whereas polymers are usually spin-coated from solution. Vacuum evaporation lends itself to easy coaling of successive layers. With solution processing, one must consider the compatibility of each layer with the solvents used for coating subsequent layers. Increasingly, multilayered polymer devices arc being described in the literature and, naturally, hybrid devices with layers of both polymer and small molecule have been made. [Pg.219]

The fluorescence color converter technique [32] can, in principle, overcome much of this power loss by replacing the white light emitter with a blue-emitting organic stack, and the absorbing filters with green and red fluorescent dyes. Thus when a green pixel is desired, the OLED underneath is turned on and the blui... [Pg.240]

There is no reason why the same principle cannot be applied for light-emitting polymers as host materials to pave a way to high-efficiency solution-processible LEDs. In fact, polymer-based electrophosphorescent LEDs (PPLEDs) based on polymer fluorescent hosts and lanthanide organic complexes have been reported only a year after the phosphorescent OLED was reported [8]. In spite of a relatively limited research activity in PPLEDs, as compared with phosphorescent OLEDs, it is hoped that 100% internal quantum efficiency can also be achieved for polymer LEDs. In this chapter, we will give a brief description of the photophysics beyond the operation of electrophosphorescent devices, followed by the examples of the materials, devices, and processes, experimentally studied in the field till the beginning of 2005. [Pg.414]

Transmission electron microscopy (TEM) is a powerful and mature microstructural characterization technique. The principles and applications of TEM have been described in many books [16 20]. The image formation in TEM is similar to that in optical microscopy, but the resolution of TEM is far superior to that of an optical microscope due to the enormous differences in the wavelengths of the sources used in these two microscopes. Today, most TEMs can be routinely operated at a resolution better than 0.2 nm, which provides the desired microstructural information about ultrathin layers and their interfaces in OLEDs. Electron beams can be focused to nanometer size, so nanochemical analysis of materials can be performed [21]. These unique abilities to provide structural and chemical information down to atomic-nanometer dimensions make it an indispensable technique in OLED development. However, TEM specimens need to be very thin to make them transparent to electrons. This is one of the most formidable obstacles in using TEM in this field. Current versions of OLEDs are composed of hard glass substrates, soft organic materials, and metal layers. Conventional TEM sample preparation techniques are no longer suitable for these samples [22-24], Recently, these difficulties have been overcome by using the advanced dual beam (DB) microscopy technique, which will be discussed later. [Pg.618]

Assuming that some of the physical and chemical mechanisms just reviewed are predominant in the formation of organic aerosol, various schemes can be derived that permit a more quantitative description of the time evolution of atmospheric organic aerosol. For example, a kinetic scheme has been proposed recently (Grosjean and Friedlander, unpublished data) for aerosol formation from ole ic precursors that may be applied in principle to other hydrocarbon classes. Starting with this system. [Pg.90]

The fundamental electro-optical principles of LCDs and OLEDs with their relative advantages and disadvantages for a diverse range of specific applications are described in this monograph. These specifications then prescribe the... [Pg.242]

As noted above, observations of large enhancements of the photoluminescence are insufficient to guarantee utility for application of plasmon-enhanced emission in OLEDs where the excited state is not photogenerated. In principle, increases in photoluminescence observed exfierimentally could be completely due to absorption enhancement. Even observation of reduced excited state lifetimes in conjunction with increased emission is insufficient to prove radiative rate enhancement since the lifetime reduction could be due to excited state quenching by the metallic surface and compensated by large absorption enhancements. [Pg.550]

In the scope of this chapter, organometallic triplet emitters are of particular interest due to their promising use in electro-luminescent devices such as OLEDs (organic/organometallic light emitting diodes). (See for example [11-16].) In Sect. 2, the construction and working principle of an OLED is... [Pg.2]

Fig. 5.2 Device configuration and working principle of OLEDs. (a) a triple-layer device showing a hole-transporting layer (HTL), emissive layer (EML) and electron-transporting layer (ETL) sandwiched between two electrodes (b) a double-layer device. An energy diagram showing hopping transport of holes and electrons in (c) a triple-layer device and (d) a double-layer device. Light comes out upon radiative decay of excitons. Fig. 5.2 Device configuration and working principle of OLEDs. (a) a triple-layer device showing a hole-transporting layer (HTL), emissive layer (EML) and electron-transporting layer (ETL) sandwiched between two electrodes (b) a double-layer device. An energy diagram showing hopping transport of holes and electrons in (c) a triple-layer device and (d) a double-layer device. Light comes out upon radiative decay of excitons.

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