Transparent cathodes

OLEDs are normally fabricated on a transparent substrate and therefore on top of a transparent anode. However, several potential applications, such as micro-displays integrated on a crystalline silicon chip or a totally transparent OLED array for a heads-up display, require a transparent top electrode. There has been some work published describing the development of transparent cathodes. The most obvious approach is to use a very thin metal layer, such as Mg Ag, overcoated with a transparent conductor, such a.s ITO [94]. This is not so trivial as it appears, since the cathode metal must survive the reactive sputtering process employed to deposit the ITO. Another approach uses no metal but rather a CuPc layer between the electron-transporting Alqs and the ITO [95]. It is suggested dial the oxidative environment during ITO deposition results in heavy n-type doping near the CuPc interface. 

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A regenerative photogalvanic cell with oxidative quenching (Fig. 5.58b) is based, for example, on the Fe3+-Ru(bpy)2+ system. In contrast to the iron-thionine cell, the homogeneous photoredox process takes place near the (optically transparent) cathode. The photoexcited Ru(bpy)2+ ion reduces Fe3+ and the formed Ru(bpy)3+ and Fe2+ are converted at the opposite electrodes to the initial state. 

FIGURE 6.24 (a) Luminous efficiency of two top-emitting OLEDs with a configuration of glass/Ag (200 nm)/ITO (130 nm)/PEDOT (80 nm)/Ph-PPV (80 nm)/semi transparent cathode (closed circles), and Al-PET/acrylic layer/Ag (200 nm)/CFx (0.3 nm)/Ph-PPV (110 nm)/semitransparent cathode (open diamonds), (b) A photo image showing a flexible top-emitting electroluminescent device on an Al-PET substrate. 

Fig. 25. Schematic device structures of (a) TEOLED with transparent cathode and (b) conventional OLED.

However, to realize making reverse OLEDs, it is necessary to carry-out both the theoretical and technological researches to find out appaopriate materials which can be used for the transparent cathode. 

The DSSCs represent a relatively new class of low-cost solar cells with great promise, which contains a transparent cathode, a highly porous semiconductor layer with a soaked layer of dye, an electrolyte solution and a... 

Based on implemented pattern, the sunbeams entered into the photoactive layer with 4-10 mm active area by passing through a 10 nm of lithium fluoride/aluminum (LiF/Al) layer as semi-transparent cathode outer electrode. 

Optically transparent cathode electrodes can also be used for achieving top or bidirectional light... 

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