Efficient organic electroluminescent (EL) devices were fabricated by using a highly fluorescent aluminum complex, tris(4-methyl-8-quinolinolato)aluminum(III) (Almq3), as an emitter layer. In addition to using this complex, a multilayer device structure, consisting of a hole-injecting layer, a hole transport layer, a dye-doped Almq3 emitting layer, and an electron transport layer, was employed in order to reduce the driving voltage as well as to maximize carrier recombination efficiency. From this device, a maximum luminance of over 140 000 cd/m2 and an external quantum efficiency of 7.1% was observed, which is the highest efficiency ever reported for organic EL devices.
We present measurements of the absolute photoluminescence (PL) quantum yield, φPL, for a wide variety of organic compounds in solid films, pure and molecularly doped with strongly fluorescent materials. The procedure, which uses an integrating sphere, does not entail comparison to other standards, and provides accurate measure of the photoluminescence efficiency for submicron thick films, prepared by high vacuum vapor deposition. Host materials include N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4-4′-diamine (TPD), a common hole transport material for light emitting diodes, tris (8-hydroxyquinolinolato) aluminum (III) (Alq3) and its methyl derivative, Almq3, two aluminum chelates used as electron transport and/or green emitting materials. Dopants include tetraphenylnapthacene (rubrene) and N,N′-diethyl quinacridone (DEQ). Doping results in a substantial increase (∼a factor 2–4) of φPL in comparison with that of the pure host. For instance, measured φPL increases from 0.25 and 0.42 for pure Alq3 and Almq3, respectively, to near unity upon doping with rubrene at a concentration of ∼1 mol %. The above data are discussed within the framework of Förster energy transfer from host to guest.
Infrared and photoluminescence spectra of matrix-isolated and thin-film samples (both at 11 K) of tris(8-hydroxyquinolinato)aluminum(III) (Alq3) and tris(4-methyl-8-hydroxyquinolinato)aluminum(III) (Almq3) were
collected and compared to vibrational spectra generated by B3LYP based density functional calculations.
The present infrared spectral results suggest that both Alq3 and Almq3 exist primarily in the meridional or C
1
isomeric form with little or no spectral evidence for the presence of the alternate, facial (C
3 symmetry) geometric
isomer. In addition, photoluminescence spectra of these molecules isolated in an argon matrix show vibronic
structure in the emission band associated with the S1 → S0 transition.
A green-light-emitting aluminum complex, tris(4-methyl-8-quinolinolato)Al (III) (Almq3), was synthesized and used as an emitter material in organic electroluminescent (EL) devices. The device structure of glass substrate / indium-tin oxide / tetraphenyldiamine derivative / Almq3 / Mg:Ag was employed. The EL device exhibited efficient green light originating from Almq3 with a maximum luminance of 26000 cd/m2 at 14 volt. The maximum external quantum efficiency was 2.5% photons / electron.
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