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27 February 2002 Cathodes incorporating thin fluoride layers for efficient injection in blue polymer light-emitting diodes
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Abstract
Efficient blue Polymer Light-Emitting Diodes (PLEDs) were fabricated by evaporating thin LiF layers between Al or Ca cathodes. Electroabsorption measurements of the built-in potential across the diodes show that devices fabricated with LiF/Ca/Al cathodes exhibit the smallest average barrier height and operating voltage (compared to both Ca and LiF/Al currently amongst the most efficient electron injectors). The turn-on bias is essentially equivalent to the built-in potential (~2.7 V), indicating an effective minimisation of the barrier to electron injection. Results are also compared with devices incorporating CsF layers and are correlated with the electroluminescent characteristics of the LEDs. A very strong dependence (~ exponential) between the built-in potential and the current and luminance at a fixed electric field (0.5MV/cm) is observed and is explained with the reduction of the cathodic barrier height brought about by the different cathode multilayers.
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Thomas M. Brown, Ian S. Millard, David Lacey, Jeremy H. Burroughes, Richard H. Friend, and Franco Cacialli "Cathodes incorporating thin fluoride layers for efficient injection in blue polymer light-emitting diodes", Proc. SPIE 4464, Organic Light-Emitting Materials and Devices V, (27 February 2002); https://doi.org/10.1117/12.457463
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