Tris(8-Hydroxyquinoline) Aluminum/2-(4-Biphenylyl)-5-(4-Tertbutylphenyl)-1,3,3-Oxadiazole Organic Multiple Quantum Wells for Electroluminescent Devices

Organic multiple quantum wells(OMQWs) consisting of alternating layers of organic materials have been fabricated from tris(8-hydroxyquinoline) aluminum(Alq)and 2-(4-biphenylyl)-5-(4-tertbutylphenyl)-1,3,3-oxadiazole(PBD) by a multisource-type high-vacuum organic molecular deposition.From the small-angle X-ray diffraction patterns of Alq/PBD OMQWs,a periodically layered structure is confirmed through the entire stack.The Alq layer thickness in the OMQWs was varied from 1 nm to 4 nm.From the optical absorption,photoluminescence and electroluminescence measurements,it is found that the exciton energy shifts to higher energy with decreasing Alq layer thickness,The changes of the exciton energy could be interpreted as the confinement effects of exciton in the Alq thin layers.Narrowing of the emission spectrum has also been observed for the electroluminescent devices (ELDs) with the OMQWs structure at room temperature.

Fabrication of Green Electroluminescent Devices

A gadolinium ternary complex, tris(1 phenyl 3 methyl 4 isobutyryl 5 pyrazolone) (2, 2′ dipyridyl) gadolinium Gd(PMIP) 3(Bipy) was synthesized and used as a light emitting material in the organic electroluminescent devices. The devices exhibited the green electroluminescent (EL) emission peaking at 513 nm, originating from the Gd(PMIP) 3(Bipy). By improving the configuration, the device with a structure of ITO/poly(N vinylcarbazole) (PVK) (40 nm)/Gd(PMIP) 3(Bipy) (40 nm)/tris (8 hydroxyquinoline) aluminum (ALQ) (40 nm)/Mg∶Ag(200 nm)/Ag(100 nm) showed higher performance and a maximum luminance of 340 cd·m -2 at 18 V.

Green Light-Emitting Organic Electroluminescent Device with a New Fluorescent Dye Dispersed in Poly(N-vinylcarbazole) Emitter Layer

Double-layer organic electroluminescent devices have been constructed. A new fluorescent dye, 9,10-bis(phenylethynyl)anthracence, was chosen as the dopant which was molecularly dispersed in the polymer film, and green light was observed from the device with luminance of 130cd/m(2) at 17V.

Enhancement of Stability of Polymer Light-Emitting Diodes by Post Annealing

We investigate the effect of thermal annealing before and after cathode deposition on the stability of polymer light-emitting diodes （PLEDs） based on green fluorescent polyfluorene derivative. The annealed PLEDs exhibit improved charge transport and red-shift emission compared to the as-fabricated device. The stability of the PLEDs is largely enhanced by post-annealing before and after Ca deposition, which is attributed to the enhanced charge transport and the intimate contact between the cathode and the emissive layer.

Influences of Injection Barrier and Mobility on Recombination Rate and Zone in OLEDs

The luminous efficiency of organic light-emitting devices depends on the recombination probability of electrons injected at the cathode and holes at the anode. A theoretical model to calculate the distribution of current densities and the recombination rate in organic single layer devices is presented taking into account the charge injection process at each electrode, charge transport and recombination in organic layer. The calculated results indicate that efficient single-layer devices are possible by adjusting the barrier heights at two electrodes and the carrier mobilities. Lowering the barrier heights can improve the electroluminescent(EL) efficiency pronouncedly in many cases, and efficient devices are still possible using an ohmic contact to inject the low mobility carrier, and a contact limited contact to inject the high mobility carrier. All in all, high EL efficiency needs to consider sufficient recombination, enough injected carriers and well transport.