Search

We report photo and electroluminescence efficiency of a thiophene oligomer functionalized to enhance its solid-state efficiency. We find that the absolute PL quantum yield is up to 37% for spin-coated thin films of the compound. The material has been used as active material in organic light-emitting diodes (LEDs). EL efficiencies up to 0.9 cd/A are demonstrated in LEDs prepared with a blend indium tin oxide and Ca–Al electrodes.

The light output and the current driving tris-(8-hydroxyquinolinato) aluminum (III) (Alq3)-based light-emitting diodes were found to increase by up to 5% and 3%, respectively, as an external magnetic fiel increased to 300 mT. The positive magnetic field effects were sensitive to the applied voltage. These observations made clear that the emissive singlet exciton formation proceeds via a correlated electron–hole pair state and the excitonic injection of electrons contributes to the driving current, the concentration of singlet excitons being modulated by the hyperfine scale magnetic- field-dependent mixing of singlet and triplet pair states constituting precursors of molecular excitons.

Polyconjugated regular bithiophene-alt-thiophene-S,S-dioxide copolymers were produced by anodic coupling of variously 3,4-ethylenedioxy-substituted 2,5-bis(2-thienyl)thiophene-S,S-dioxide. The polymers were characterized by cyclic voltammetry, FTIR reflection-absorption and UV-vis spectroscopy, MALDI-TOF mass spectroscopy, electrochemical quartz crystal microbalance, in situ ESR and in situ conductivity techniques, photo- and electroluminescence measurements. The regular alternation of electron-rich and -poor thiophene rings in the polymer chain operated by the ethylenedioxy and S,S-dioxide moieties produces a finite window of conductivity. Alkylprotection of the b-positions of the thiophene-S,S-dioxide ring gave low-defect and soluble oligomers which were investigated in single-layer organic light-emitting devices (OLEDs). Photoluminescence quantum efficiency of ca. 1% and external electroluminescence quantum efficiencies of 0.01% photon/electron at a luminance of 100 cd m2 were obtained.

Organic electroluminescent (EL) single-layer (SL) and double-layer (DL) light-emitting diodes were fabricated based on 4,4',4''-tris[3-methylphenyl(phenyl)amino] triphenylamine (m-MTDATA) and 2-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) molecules incorporated in bisphenol-A-polycarbonate (PC)matrix. The external EL quantum efficiency of the dominating exciplex emission of the indium tin oxide (ITO)/m-MTDATA:PBD:PC/Ca SL structure is >0.4% photon/electron and that from the ITO/m-MTDATA:PC/PBD/Ca DL device exceeds 1% photon/electron. The operating voltage of the DL device at maximum efficiency is 4.8 V and the onset voltage of the EL is as low as 2.0 V. The photoluminesce quantum efficiency of the exciplex is greater than 17%. The high exciplex emission-based EL yield from the DL device is attributed to the narrow recombination zone imposed by the high energy barriers for the electron and hole transfer at the (m-MTDATA:PC)/PBD interface.

Fluorescence excitation (FE)spectra of Al(III) 8-hydroxyquinoline solid films in contact with quartz, metal and some red-emitting dyes were measured and related to the FE spectrum recorded from the uncovered film surface. Their profiles indicate that singlet excitons are quenched by the surface and near-surface energy acceptors. The quenching efficiency dependence on penetration depth of the eciting light is a result of both diffusion of singlet excitons toward the surface and their reactions with exponential distribution of quenching centres in the films. It is possible to fit the calculated quenching vs. penetration curves to the experimental date if values of the diffusion length of singlet excitons = 30nm or the penetration depth of the quenching centres from the surface into the bulk of the order of 100-1000 nm are used. Possible origin of quenching centres and the quenching effect on quantum electroluminescence yield of organic light-emitting diodes based on Alq3 emitter are briefly discussed.