Oriented phosphorescent emitters boost OLED efficiency

• Published in: Organic electronics Vol. 12; no. 10; pp. 1663 - 1668
• Main Authors: Flämmich, Michael, Frischeisen, Jörg, Setz, Daniel S., Michaelis, Dirk, Krummacher, Benjamin C., Schmidt, Tobias D., Brütting, Wolfgang, Danz, Norbert
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.10.2011; Elsevier
• Subjects: Applied sciences; Electronics; Emitter orientation; Exact sciences and technology; In situ characterization; Optoelectronic devices; Organic light-emitting diode; Phosphorescent emitter; Photoluminescence; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Organic light-emitting diode; In situ characterization; Phosphorescent emitter; Emitter orientation; Photoluminescence; Performance evaluation; In situ; Transmitter; Optimization; Light emitting diode; Optoelectronic device; Organic light emitting diodes; Optical method; Phosphorescence; Quantitative analysis; Organic electronics
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2011.06.011

[Display omitted] ► OLED triplet emitter Ir(MDQ) 2(acac) blended in α-NPD matrix is studied. ► Polarized emission patterns are analyzed under electrical and optical excitation. ► Unexpected non-isotropic, mainly parallel emitter orientation is found. ► Parallel emitters increase outcoupling efficiency by ∼50% compared to isotropic case. ► Promising approach for efficiency enhancement of phosphorescent guest–host systems is revealed. The orientation distribution of the emissive sites in a phosphorescent Organic LED has been measured utilizing two independent optical methods. In contradiction to common expectations we find a clearly non-isotropic, predominantly parallel emitter orientation in the well-known triplet emitting guest–host system of Ir(MDQ) 2(acac) blended in an α-NPD matrix. This result emphasizes the necessity of more sophisticated assumptions on active emitter properties in quantitative optical OLED analysis, and demonstrates a highly promising approach for OLED efficiency optimization.