Double-layer LED

The recombination width can be minimized by the confinement of the recombination process at the interface of two organic materials as typically occurs in double- and multi-layer organic LEDs [2] (see also Chapter 5). The penetration depths of holes and electrons can then be identified with thicknesses of hole and electron transporting layers, respectively, and their mobilities used to calculate the recombination width. A good example of such a situation is the recombination process in the most studied double-layer LED, ITO/TPD/Alq3/Mg/Ag. The free carrier kinetics at the TPD/Alq3 interface after an abrupt switch of the voltage off takes on a simple form... 

LEDs were fabricated with TA-PPP as the emissive layer. Single-layer devices of ITO/PEDOT/TA-PPP/Ca/Al were fabricated. PEDOT, poly(3,4-ethylenedioxythiophene), was used to enhance hole injection from the anode. Charge injections of the single layer LEDs were clearly hole dominant The barrier for electron injection, around 1.0 eV, is too high. Electron dominant materials such as DO-PF and 2-(4-t-butylphenyl)-5-biphenyloxadiazole (t-PBD) were used to enhance electron injection. The thin film of a TA-PPP and PF blend (95 5 weight ratio) was phase separated. Atomic force microscopy (AFM) showed PF spheres, close to 1 pm in diameter, dispersed in the TA-PPP matrix (Figure 6). This type of phase separation is common in blends of stiff and soft polymers. The PL emission of die blend film was characteristic of TA-PPP. However, once thermally treated, the spectrum shifted bathochromically much like PF. The EL spectrum from LEDs based on the blend thin film contained much emission from PF in the 500-700 nm regime. The device efficiency was about 0.43 cd/A. TA-PPP/PF double layer LEDs were also fobricated. But the efficiency was not improved because when PF was spin coated onto TA-PPP, the PF solution washed out most of the TA-PPP layer. 

Polarized Electroluminescence from Double-Layer LEDs with Active Film Formed by Two Perpendicularly Oriented Polymers... 

The heterostructure of the active double layer LED was been chsuacterized by atomic force microscopy (AFM) (lO) domains oriented orthogonally are clearly recognized. 

Table 16-6. Electrical properties and efficiencies of single-layer and double-layer OPVS-LEDs with 1TO hole-injecting contacts in forward-bias operation.

Every cell possesses a plasma (or cell) membrane which isolates its contents from its surroundings. This membrane consists of a double layer of phospholipid molecules with proteins attached or dispersed within. The uneven distribution of proteins and their ability to move in the plane of the membrane led to the description of this structure as a fluid mosaic (Figure 1.2) (Chapter 5). Some of these proteins facilitate the transport of molecules and ions through the membrane, while others are receptors for extracellular molecules which provide information about conditions in adjacent cells, blood and elsewhere in the body. Physical or chemical damage to these membranes can render them leaky so that, for example, Na and Ca ions, the concentrations of which are much higher in the extracellular fluid, can enter the cell causing damage. On the outer surface of... 

The deviations from the Szyszkowski-Langmuir adsorption theory have led to the proposal of a munber of models for the equihbrium adsorption of surfactants at the gas-Uquid interface. The aim of this paper is to critically analyze the theories and assess their applicabihty to the adsorption of both ionic and nonionic surfactants at the gas-hquid interface. The thermodynamic approach of Butler [14] and the Lucassen-Reynders dividing surface [15] will be used to describe the adsorption layer state and adsorption isotherm as a function of partial molecular area for adsorbed nonionic surfactants. The traditional approach with the Gibbs dividing surface and Gibbs adsorption isotherm, and the Gouy-Chapman electrical double layer electrostatics will be used to describe the adsorption of ionic surfactants and ionic-nonionic surfactant mixtures. The fimdamental modeling of the adsorption processes and the molecular interactions in the adsorption layers will be developed to predict the parameters of the proposed models and improve the adsorption models for ionic surfactants. Finally, experimental data for surface tension will be used to validate the proposed adsorption models. 

Considerations of convenience and economy have led us to restrict the scope of this work in several ways. We have excluded electrochemical techniques, such as conductometry, high-frequency conductometry, and dielectro-metry,i, in which neither the electrical double layer nor any electrode reaction need be considered. These furnish information so widely different from, and so rarely used in conjunction with, that provided by polarography and its congeners that combining them would be difficult and of little use. 

For a nonpolarizable double layer, the charges led in or out of the electrode from the outer circuit are equivalent to a capacitance C = dqH/dV). However, this would be a pseudo-capacitance because the charge penetrates the double layer. ads can be calculated from Eq. (10.5). 

The admittance response at 1 kHz has also been interpreted in terms of the behavior at residual defects in anodic films. This interpretation is based on electron optical characterization, which shows that anodic films contain a distribution of preexisting defects associated with substrate inclusions and mechanical flaws (96,102). In aggressive environments, pits nucleate from these defects and propagate into the metal substrate. In this model, pits are distinct from anodic film flaws, and both can contribute to the measured admittance. Measurements of anodic films exposed to chloride solutions showed that the dissipation factor increased with time, but the capacitance remained nearly constant. Under these conditions, pit propagation at a flaw led to a pit area increase, which increased the resistive component of the admittance, resulting in an increased dissipation factor, but no increase in the capacitance. Measurements at 100 kHz were reflective of the electric double layer and not the components of the oxide film. 

Dec. 6,1869, Wells, Norfolk, England - Jan. 17,1958, Oxford, England) Chapman studied in Oxford, and then he was a lecturer at Owens College (which later became part of the University of Manchester). In 1907 he returned to Oxford, and led the chemistry laboratories of the Jesus College until his retirement in 1944 [i]. Chapmans research has mostly been focused on photochemistry and chemical kinetics however, he also contributed to the theory of electrical -> double layer [ii]. His treatment of the double layer was very similar to that elaborated by -> Gouy earlier, and what has come to be called the Gouy-Chapman double-layer model [i.iii]. 

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