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Spiro compounds as organic antireflexion coatings for transparent OLEDs Disclosure Number: IPCOM000175565D
Publication Date: 2008-Oct-14
Document File: 3 page(s) / 81K

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Spiro compounds as organic antireflexion coatings for transparent OLEDs

Transparent OLEDs have electrodes as least partly transparent to emit light to both sides (top- and bottom emitter). To obtain a high transparency of the switched-off OLED, one or more antireflexion layers are prepared on top of the top-electrode. The material for the antireflexion layers shall have an refractive index as high as possible.

This article discusses a group of materials with a high refractive index: spiro compounds exhibiting with n = 1.96 for Spiro-6PP as an example. Simultaneously the glass transition temperature

       1of Spiro compounds is often very high. This is advantageous for subsequent process steps at high temperatures, or in case of the application of OLEDs at high operation temperatures (e.g. in cars).

Areas of application are transparent OLEDs as room illumination integrated in windows or cars (e.g. car-windows), or as emergency signage to be shown on demand on front shields of cars. Other areas of application are OLED room separators, OLED luminaires etc. Spiro compounds are further interesting as light out-coupling layers, especially if the transparent electrode is a thin metal layer or a metal layer stack comprising conductive oxides.



Fig.2: examples for Spiro compounds: a) Spiro-Sexiphenyl (Spiro-6PP); b) 4-Spiro2.

A common transparent OLED comprises a substrate, a transparent electrode on top of the substrate (e.g. the anode), organic charge transport and emission layer(s) and a further transparent electrode (e.g. the cathode). Especially in case of a thin metal electrode (or stack of metal layers), the transparency of the OLED can be enhanced by additionally applied antireflexion coatings. The OLED will further be encapsulated by a at least partly transparent cover lid.

1the temperature, where the amorphous state transfers to the (poly-)crystalline state

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The transparent electrodes may consist of at least one of the following materials:
 Thin metal layers or metal layer stacks comprising Al, Ag, Yb:Ag, Au, etc. with a thickness of 1 to 100 nm, typically 10-30 nm.

 Transparent conductive oxides such as ITO, ZnO, etc. in single or multilayer stacks with thicknesses of 1 to several 100 nm, typically 10-70 nm. In many cases an additional organic layer stack is added as a buffer layer, e.g. copper-phthalocyanine, preventing the functional organic layer stack from damages during the preparation process

 Combinations of both material classes.

The light out-coupling layer may comprise at least one of the following materials:
 Inorganic materials with high band gap such as ZnS or ZnSe with thicknesses of 1 to several 100 nm, typically 5-60 nm.

 Organic layers such as Alq3 or -NPD or spiro compounds with layer thicknesses of 1 to several 100 nm, typically 10-80 nm.

Two examples of organic spiro compounds as light out-coupling layers are spiro-sexiphenyl (Spiro-6PP) and...