Influences of central metal ions on the electroluminescene and transport properties of tris-(8-hydroxyquinoline) metal chelates

A series of tris-(8-hydroxyquinoline) metal chelates with central metal ions of Al3+, Ga3+, and In3+ was synthesized, characterized, and used in organic electroluminescent devices. The ionization potential and optical band gap of the three chelates were measured by ultraviolet photoelectron spectroscopy and ultraviolet-visible spectrum, respectively. Two types of devices, with configurations of indium tin oxide (ITO)/N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) (80 nm)/Mq(3) (80 nm)/Mg:Ag (200 nm) and ITO/TPD (60 nm)/TPD:rubrene (3%) (20 nm)/Mq(3) (80 nm)/Mg:Ag (200 nm) (M=Al, Ga, or In), were fabricated and characterized based on these metal chelates. In the first type of configuration, the metal chelates were used as both the emitter and the electron-transporting layer. In the second type of configuration, the metal chelates were believed to only act as electron-transporting layer. As the central ion changed, both the luminescence and the carrier transport properties of the metal chelates were changed. By comparing the performance of the two types of devices, we found that as the size of the metal ion increased, the luminance efficiency decreased and the electron mobility increased. (C) 2003 American Institute of Physics.