High efficiency p-i-n top-emitting organic light-emitting diodes with a nearly Lambertian emission pattern

We report high efficiency phosphorescent green p-i-n top-emitting organic light-emitting diodes consisting of metal anodes (Ag and Al), a rhenium oxide p-dopant, a rubidium carbonate n-dopant, and a semitransparent Ag cathode. Significantly high peak current efficiencies of 88 and 73 cd/A are demonstrated for the devices using Ag and Al anodes, respectively, through the optimization of organic layer thickness. The electroluminescence intensities of the Ag-based device with viewing angles show a nearly Lambertian distribution, whereas those of the Al-based device exhibit a relatively strong angular dependence, which is mainly attributed to the change in the resonance wavelength of the microcavity of the devices. Efficiencies, emission spectra, and angular dependence of the emission of the devices are further successfully analyzed using an optical model. (C) 2009 American Institute of Physics. [doi:10.1063/1.3225998]