Enhanced electroluminescence and reduced efficiency roll-off in electrophosphorescent devices using a very high electron mobility material as emitter host and electron transporter

• Published in: Journal of physics. D, Applied physics Vol. 42; no. 6; pp. 065103 - 065103 (4)
• Main Authors: Li, T L, Li, W L, Chu, B, Su, Z S, Chen, Y R, Han, L L, Zhang, D Y, Li, X, Zang, F X, Sum, T C, Huan, A C H
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 21.03.2009; Institute of Physics
• Subjects: Applied sciences; Electronics; Exact sciences and technology; Optoelectronic devices; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Performance evaluation; Luminance; Optoelectronic device; Transmitter; Doped materials; Electron mobility; Electroluminescence; Phosphorescence; Quantum yield; Light emitting diode
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/42/6/065103

We demonstrate markedly improved electroluminescence (EL) intensity and reduced external quantum efficiency (EQE) roll-off of a device which presents two emitting layers of @@ifac@-tris-(2-phenylpyridine) iridium [Ir(ppy)@d3] in 4,4'-bis(9-carbazolyl)-2,2'-biphenyl (CBP) and 1,3-bis[2-(2,2'-bipyridine-6-yl)-1,3,4-oxadiazo-5-yl]benzene(Bpy-OXD); 4,7-diphenyl-1,10-phenanthroline/Bpy-OXD layers were used as hole blocking and electron transport layers. The device exhibits a maximum EQE of 15.5% (corresponding to an efficiency of 56.8 cd A@@u-1@) at a luminance of 600 cd m@@u-2@, which is twice the value (8.2%) of the reference diode using Ir(ppy)@d3 doped CBP as a single emitting layer; the device still maintained a 6.5% efficiency at a luminance of 70 450 cd m@@u-2@. The mechanism of this marked improvement in EL intensity and decrease in the EQE roll-off was also explored in detail.