Damping Effect of a Continuous Mass-Distributed Viscoelastic Layer.

Adachi, Eiji; Maeda, Kouzou; Miyaji, Kazuhiro

doi:10.1299/kikaic.58.390

Cited by 1 publication

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“…Due to the interfacial dipole layer formation, the power efficiency and the electro-luminescence efficiency are dependent also on the thickness of the deposited alkali metal layer, as figured out by the following pictures (Fig. 4 a) and b)) [5,22] . Figure 4 shows that a great enhancement in the power efficiency is achieved using a Cs layer thinner than 30 Å and, inside the same architecture, using a Li layer thinner than 60 Å.…”

Section: Double Layer Cathodementioning

confidence: 96%

“…So far the combination of alkali metals with organic in such a configuration has been tested using Alq3 [5,10] and POPy 2 [10] , whilst in general any metal cap can be adopted together with the alkali metal (Cu, Al, Ag, Au, MgAg and Mg have been tested) [4,5,9] [5] b) current density-voltage (J-V) characteristics for the same device built up using Li instead of Cs for different Li thicknesses, from 0.5 nm to 10 nm (courtesy of Prof. C. Adachi). [22] 1.1.2. ETL doping by alkali metals Co-deposition of the organic ETL and the alkali metal like Li or Cs (Fig.…”

Section: Double Layer Cathodementioning

confidence: 99%

“…As a side effect of the adoption of alkali metals inside the OLED structure, the organic materials experienced longer lifetime and stability due to the reduced electrical stresses. The device exploiting alkali metals can reach the same performances of a standard device using lower driving voltages and thus lower electric fields [13,22] (see fig.1 below). Starting from lab scale tests, the requirements for a high external quantum efficiency and high power efficiency have now reached the mass production stage.…”

mentioning

confidence: 97%

“…Organic lifetime seems to be increased by a factor more than 1000 using Cs layer (Courtesy of Prof. C. Adachi). [22] …”

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confidence: 99%

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Alkali metal sources for OLED devices

et al. 2005

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Objective and backgroundOne of the key issues for organic light emitting diodes (OLEDs) is to achieve high electro-luminescence external quantum efficiency (η ext ), high power efficiency (η E ) [1] and long-term stability. These goals imply extremely efficient electron injection and thus low driving voltage, together with high electron mobility in the organic layer and therefore high recombination efficiencies. The cathode structure and the metal-organic (M-O) interface are the major responsible for the desired performance improvements. Since 1987 Tang and Van Slyke [2] adopted a cathode structure based on composite MgAg alloy able to reduce the overall cathode work function and the barrier height for the electron injection. Recently, these OLED issues have been examined in the context of optimizing electron injection through the incorporation of an alkali metal inside the cathode structure. The first appearance of alkali metals to obtain a low driving voltage OLED was in 1983, when Partridge used Na, K and Cs as efficient electron injection cathodes in a PVK based OLED [3] . In the present work and in broad literature works, deep studies have been carried out on the usage of Li and Cs. Alkali metals incorporation in the OLED structure can be accomplished in two forms:o ultra-thin layers (Li, LiAl, Li 2 O, LiF, Cs, CsAl, CsF and alkali-metal carboxilates) above the electron transport layer (ETL) and capped by an Al back electrode [4][5][6][7][8] o co-deposition of Li or Cs with an ETL immediately prior to the cathode deposition [9][10][11][12][13][14][15][16][17] (also named "alkali metal doping of ETL") Both configurations have been shown to dramatically reduce the drive voltages and, in the meantime, increase the external quantum efficiency, the overall luminance and the long-term operational stability. Moreover, the creation of an electron injection layer (EIL) both by the interlayer between ETL and cathode and by ETL doping, employing transparent cathodes, such as ITO, has been shown excellent improvements in both η ext and η E also for Top-Emission device architectures (TOLEDs) [18] and for Stacked structures (SOLEDs). Transparent cathodes built up using CuPc or BCP capped with RF sputtered ITO, are conformal with the adoption of an alkali metal like Li. Such cathodes structures are useful for OLEDs integrated with silicon TFT driver electronics for Active-Matrix displays (AMOLEDs), micro-emissive displays, head-up displays, white displays as backlighting. Finally, alkali metals have been successfully used also in PLED structures, mainly in conjunction with standard polymers like MEH-PPV, and with metallic cathodes like Al and Au [19][20][21] . As a side effect of the adoption of alkali metals inside the OLED structure, the organic materials experienced longer lifetime and stability due to the reduced electrical stresses. The device exploiting alkali metals can reach the same performances of a standard device using lower driving voltages and thus lower electric fields [13,22] (see fig.1 below). Starting fro...

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Section: Double Layer Cathodementioning

confidence: 96%