Luminance enhancement

The luminance enhancement was observed with the free-standing anodic alumina film by the naked eye because of anisotropic light scattering by spatially arranged nanometer-size pores. Fig. 1 demonstrates a high transparency of the free-standing anodic alumina film produced as compared to the reference Kimoto PF-90S M/M scattering film. 

The general complexity in the fabrication of dielectric mirrors and their strong wavelength-dependent reflection properties makes it very difficult for them to be implemented in real OLED displays. In view of these, microcavity OLEDs using metal mirrors (one reflective and one semi-transparent/reflective, Figure 9.10d and e) are more practical for display applications [3,10,27-29,33]. However, due to absorption (loss) in metals, it is not clear whether one can still obtain luminance enhancement as in microcavity OLEDs using lossless dielectric mirrors, and it is also not clear to what degree and under what conditions one obtains most luminance enhancement. 

FIGURE 10.14 PEDT PSS as hole injection layer for polymeric emitters enhanced luminance, enhanced quantum-efficiency, and enhanced power-efficiency. 

Figure 14,13 PEDOT PSS as hole injection layer for polymeric emitters enhanced luminance, enhanced quantum efficiency and enhanced power efficiency. From 5. Kirchmeyer and K. Reuter, Scientific importance, properties and growing applications of poly(3,4-ethylenedioxythiophenes), J. Mater. Chem. 15, 2077 2088 (2005). Reproduced by permission of The Royal Society of Chemistry...

Formation of Na+, K+-ATPase carrier molecules in the basolateral membrane of the tubular epithelial cells (promotes extrusion of Na+ ions from the cells and their movement into plasma by way of peritubular capillaries enhances the concentration gradient for passive diffusion through Na+ channels in the luminal membrane)... 

Potassium secretion is enhanced by aldosterone. As the concentration of K+ ions in the extracellular fluid increases, the secretion of aldosterone from the adrenal cortex also increases. The mechanism of action of aldosterone involves an increase in the activity of the Na+, K+ pump in the basolateral membrane. Furthermore, aldosterone enhances formation of K+ channels in the luminal membrane. 

The enhancement in luminous efficiency achieved by inserting an ultrathin interlayer between the ITO and NPB is mainly due to the reduction of hole injection from ITO to NPB in OLEDs. For a simple approximation, luminous efficiency (rj) can be related directly to a ratio of the recombination current (/r) to the total current density of OLEDs (/tot). If one denotes the current contributions from holes and electrons in OLEDs as. /h and /e, respectively, then the sum of hole and electron currents, /tot. /h + /e, and tj can be expressed as... 

The primary effect of the anode modification on the enhancement in luminous efficiency and the increased stability of OLEDs can be attributed to an improved hole-electron current balance. By choosing an interlayer with a suitable thickness of a few nanometers, anode modification enables engineering of the interface electronic properties. The above results indicate that conventional dual-layer OLEDs of ITO/NPB/Alq3/cathode have an inherent weakness of instability that can be improved by the insertion of an ultrathin interlayer between ITO and HTL. The improvements are attributed to an improved ITO-HTL interfacial quality and a more balanced hole electron current that enhances the OLED performance. 

S.A. Carter, J.C. Scott, and P.J. Brock, Enhanced luminance in polymer composite light emitting devices, Appl. Phys. Lett., 71 1145-1147, 1997. 

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