2 September 2008 Highly efficient green phosphorescent organic light-emitting diodes with hybrid device geometry
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We report on the performance of green phosphorescent organic light-emitting diodes (OLEDs) based on the well-known device structure of a hole-transport layer, an emissive layer with host 4,4'-di(carbazol-9-yl)-biphenyl [CBP] and the green phosphor emitter fac tris(2-phenylpyridinato-N,C2,) iridium [Ir(ppy)3], a hole-blocking layer of 2,9-dimethyl-4,7- diphenyl-1,10-phenanthroline [BCP] and and tris-(8-hydroxyquinolinato-N,O) aluminum [Alq3] as an electron-transport layer. Using spin-coated hole-injection/transport layers with increasing ionization potentials and decreasing hole mobilities, external quantum efficiencies of up to 18.1% at 100 cd/m2 were measured in such devices. Furthermore, by removing the electron-transport layer of Alq3 and increasing the thickness of BCP, devices with efficiencies of 21.2% and 72 cd/A at 100 cd/m2 were obtained. Achieving such high efficiencies with a simplified hybrid structure in which one layer is processed from solution and only two other organic layers are deposited from the vapor phase is desirable for the fabrication of low-cost OLEDs.
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Andreas Haldi, Benoit Domercq, Asha Sharma, Richard D. Hreha, Jian-Yang Cho, Seth R. Marder, Bernard Kippelen, "Highly efficient green phosphorescent organic light-emitting diodes with hybrid device geometry", Proc. SPIE 7051, Organic Light Emitting Materials and Devices XII, 70510B (2 September 2008); doi: 10.1117/12.795363; https://doi.org/10.1117/12.795363

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