Structure of an OLED

Figure 3.26. Structure of an OLED. S = substrate (glass), ANO = anode (e.g., ITO — indium tin oxide), HIL = hole injection layer (e.g., Cu phthalocyanine), HTL = hole transport layer, EML = emission layer, ETL = electron transport layer, EIL = electron injection layer (e.g., LiF), KAT = cathode (e.g., Ag Mg, Al). The light that is generated by the recombination of holes and electrons is coupled out via the transparent anode.

Electroluminescence (EL) is the phenomenon by which electrical energy is converted into luminous energy by the recombination of electrons and holes in the emissive material [8], The basic structure of an OLED consists of a thin film of organic material sandwiched between two electrodes, an anode of high-work-function material such as indium tin oxide (ITO) on a glass substrate, and a cathode of a low-work-function metal such as calcium (Ca), magnesium (Mg), or aluminum (Al) or an alloy such as Mg Ag. 

Fig. 13 Polarized electroluminescence (EL) spectra and device structure of an OLED containing a 35 nm thick dodecafluorene (compound 44) film at a current density of 20 mAcm-2. Used with permission [196]...

Fig. n.8 The structure of an OLED with three organic layers and a dielectric cover layer. HTL refers to the hole transport layer, EML to the emission layer, ETL to the electron transport layer. N, and k, are the optical constants of the layers (for their definitions, see Sect. 11.2.3). The dielectric is an antireflection layer. After [6, 10]. 

In practice, the structure of an OLED is more complex and may contain several additional layers, which are organic semiconductors and are introduced to enhance... 

Fig. 4.4 a Structure of an inorganic semiconductor LED b structure of an OLED c charge injection and excited state formation in an OLED. Figure adapted from Ref. [167]... 

The simplest manifestation of an OLED is a sandwich structure consisting of an emission layer (EML) between an anode and a cathode. More typical is an increased complexity OLED structure consisting of an anode, an anode buffer or hole injection layer (HIL), a hole transport layer (HTL), a light-emitting layer, an electron transport layer (ETL), a cathode... 

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. 

Fig. 4.11. Left (a) Optical microscope image of an OLED working at a luminance of 100 cd/m2 under water vapor atmosphere. Non-emitting dark spots can be seen clearly, (b) SEM image of the bubbles formed on the aluminum cathode in the dark spot area, (c) Correlation between dark spot growths (taken from the increase in diameter) and total current density [110]. Right (a) Shown here is the random pattern of carbonized areas on the surface of the cathode after operation, shown in wide field, (b) At higher resolution, the structure of one of these areas becomes more apparent, (c) and (d) show nanoscale views of carbonized areas with the extrusion of the polymer through the cathode and the resulting void underneath [111].

Fig. 1. Schematic view of an OLED showing its Fabry-Perot-like structure and the parameters used in Eq. 3.

Fig. 12.17 Energy structure of an amorphous OLED utilizing a G-H emission layer (a) and external quantum efficiency against current densityJ together with product term q, J (b).

Fig. 3.2. Basic structure of an integrated OLED pixel array/luminescent sensor film module in the back detection geometry...

Figure 11.10 shows the two most important observables of an OLED, the current densityj (left-hand ordinate) and the luminosity lo (right-hand ordinate), each in a semilogarithmic plot as a function of the applied voltage V. The structure of this OLED included no reflection-reducing cover layer over the cathode. The anode... 

Schematic diagram showing the general optical structure and characteristics of an OLED device. (From Lin, C.-L. et ei.,Appl- Phys. Sett., S7,021101-1,2005. With permission.)...

Multi-layer device. High performance of the first O-LED(l) was achieved by employing a multi-layer structure of and a diamine compound. In the double-layer OLED, the electron-accumi tion takes place and hole and electron recombines to generate excitons more easily than a single-layer device. In the P-LED, Brown et al. reported that the double-layer structure of an oxadazole compound and... 

Fig. 7.9 Left) Linearly polarized absorption and photoluminescence spectra (excitation wavelength 370 nm) of an OLED containing a 73 nm thick F(MB)10F(EH)2 film, with an inset showing the electron diffraction pattern. (Right) Device structure and polarized EL spectra of an OLED containing a 35 nm thick F(MB)10F(EH)2 film (From Culligan et al. [41])...

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