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16 February 2004 Novel cathode for organic light-emitting devices with reduced optical reflectivity
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Cathodes of Organic Light Emitting Devices (OLEDs) are typically made of low work function metals, usually resulting in highly reflective back electrodes. In high ambient illumination, the reflective back electrodes reflect the incident ambient light, resulting in a decrease in contrast of the displayed image. We developed a reduced reflectance cathode utilizing a conductive light-absorbing layer made of a mixture of metals and organic materials. Devices utilizing the reduced reflectance cathode, named Black Cathode OLEDs, demonstrate enhanced contrast even in high ambient illumination. In this work, peformance of devices with cathodes containing a mixture of tris(8-hydroxyquinoline)aluminum (AlQ3), Mg and Ag, or a mixture of AlQ3 and Ag is addressed. The studied cathodes demonstrate ~ 9 - 12% sun/eye-integrated reflectance (SEIR), ~8X lower than that of coventional metal cathodes, while device turn-on voltage and stability are comparable. In modified Black Cathode OLEDs, ~1.8% cathode SEIR has been recently realized.
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Hany M Aziz, Yoon-Fei Liew, and Zoran Popovic "Novel cathode for organic light-emitting devices with reduced optical reflectivity", Proc. SPIE 5214, Organic Light-Emitting Materials and Devices VII, (16 February 2004);

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