Interfaces electroluminescence devices

Interfaces between two different media provide a place for conversion of energy and materials. Heterogeneous catalysts and photocatalysts act in vapor or liquid environments. Selective conversion and transport of materials occurs at membranes of biological tissues in water. Electron transport across solid/solid interfaces determines the efficiency of dye-sensitized solar cells or organic electroluminescence devices. There is hence an increasing need to apply molecular science to buried interfaces. 

T. Mori, H. Fujikawa, S. Tokito, and Y. Taga, Electronic structure of 8-hydroxyquinoline Aluminium/LiF/Al interface for organic electroluminescent device studied by ultraviolet photoelectron spectroscopy, Appl. Phys. Lett., 73 2763-2765 (1998). 

C.H. Lee, Enhanced efficiency and durability of organic electroluminescent devices by inserting a thin insulating layer at the Alq3/cathode interface, Synth. Met., 91 125-127 (1997). 

A. Fukase and J. Kido, Organic electroluminescent devices having self-doped cathode interface layer, Jpn. J. Appl. Phys., 41 L334-L336 (2002). 

Okumoto K. and Shirota Y., "Exciplex formation at the oreanic solid/solid interface and tuning of the emission color in organic electroluminescent devices". Journal of Luminescence, 87-89, May 2000,1171-1173. 

Endo, J., Matsumoto, T., and Kido, J. 2002. Organic electroluminescent devices having metal complexes as cathode interface layer. ]pi.. Appl. Phys. 41 L800. 

Ishii, H., K. Sugiyama, D. Yoshimura, E. Ito, Y. Ouchi, and K. Seki (1998). Energy-level alignment at model interfaces of organic electroluminescent devices studied by UV photoemission Trend in the deviation from the traditional way of estimating the interfacial electronic structnres. IEEE J. Select. Topics Quant. Chem. 4, 24-33. 

Finally, two existing examples can be used to further illustrate this concept of doped interfaces and the p-i-n structure of the organic electroluminescent devices ... 

By 1988, a number of devices such as a MOSFET transistor had been developed by the use of poly(acetylene) (Burroughes et al. 1988), but further advances in the following decade led to field-effect transistors and, most notably, to the exploitation of electroluminescence in polymer devices, mentioned in Friend s 1994 survey but much more fully described in a later, particularly clear paper (Friend et al. 1999). The polymeric light-emitting diodes (LEDs) described here consist in essence of a polymer film between two electrodes, one of them transparent, with careful control of the interfaces between polymer and electrodes (which are coated with appropriate films). PPV is the polymer of choice. 

Fig. 13-9). The situation is different in bilayer devices, where the onset of electroluminescence corresponds mainly to charge accumulation at the organic/organic interface [123],... 

Zinc sulfide, with its wide band gap of 3.66 eV, has been considered as an excellent electroluminescent (EL) material. The electroluminescence of ZnS has been used as a probe for unraveling the energetics at the ZnS/electrolyte interface and for possible application to display devices. Fan and Bard [127] examined the effect of temperature on EL of Al-doped self-activated ZnS single crystals in a persulfate-butyronitrile solution, as well as the time-resolved photoluminescence (PL) of the compound. Further [128], they investigated the PL and EL from single-crystal Mn-doped ZnS (ZnS Mn) centered at 580 nm. The PL was quenched by surface modification with U-treated poly(vinylferrocene). The effect of pH and temperature on the EL of ZnS Mn in aqueous and butyronitrile solutions upon reduction of per-oxydisulfate ion was also studied. EL of polycrystalline chemical vapor deposited (CVD) ZnS doped with Al, Cu-Al, and Mn was also observed with peaks at 430, 475, and 565 nm, respectively. High EL efficiency, comparable to that of singlecrystal ZnS, was found for the doped CVD polycrystalline ZnS. In all cases, the EL efficiency was about 0.2-0.3%. 

It is well known that solid-state LECs exhibit a significant response time since electroluminescence can only occur after the ionic double-layers have been built up at the electrode interfaces [79,82]. Since in this case only the PFg anion is mobile, the double-layers are formed by accumulation and depletion of PFg at the anode and cathode, respectively. The LEC device with 45 started to emit blue-green light at a bias of 5 V after several minutes. The electroluminescence spectrum, as shown in Fig. 36 (trace a), is very similar to the photoluminescence spectrum recorded for a spin-coated film on glass and of a solution of the complex. For comparison, the electroluminescence... 

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