Abstract
In this work we present a detailed analysis of the emitted radiation spectrum from tris(8-hydroxyquinoline)aluminum (Alq3) based bilayer organic light emitting diodes (OLEDs) as a function of the choice ofcathode, the thickness of the organic layers, and the position of the hole transportlayer/Alq3 interface. The calculations fully take into account dispersion in the glass substrate, theindium tin oxide anode, and in the organic layers, as well as the dispersion inthe metal cathode. The influence of the incoherent transparent substrate (1 mmglass substrate) is also fully accounted for. Four cathode structures have beenconsidered: Mg/Ag, Ca/Ag, LiF/Al, and Ag. For the hole transport layer,N,N′-diphenyl–N,N′-(3-methylphenyl)–1,1′-biphenyl–4,4′-diamine (TPD) and N,N′-di(naphthalene-1-yl)–N,N′-diphenylbenzidine (NPB) were considered. As expected, the emitted radiation is stronglydependent on the position of the emissive layer inside the cavity and its distance from themetal cathode. Although our optical model for an OLED does not explicitly include excitonquenching in the vicinity of the metal cathode, designs placing the emissive layer near thecathode are excluded to avoid unrealistic results. Guidelines for designing devices withoptimum emission efficiency are presented. Finally, several different devices were fabricatedand characterized and experimental and calculated emission spectra were compared.
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