The role of molybdenum oxide as anode interfacial modification in the improvement of efficiency and stability in organic light-emitting diodes

It has been experimentally found that molybdenum oxide (MoO3) as the interfacial modification layer on indium-tin-oxide (ITO) in organic light-emitting diodes (OLEDs) significantly improves the efficiency and lifetime. In this paper, the role of MoO3 and MoO3 doped N,N '-di(naphthalene-1-yl)-N,N '-diphenyl-benzidine (NPB) as the interface modification layer on ITO in improvement of the efficiency and stability of OLEDs is investigated in detail by atomic force microscopy (AFM), polarized optical microscopy, transmission spectra, ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS).

Grain boundary conductivity of high purity neodymium-doped ceria nanosystem with and without the doping of molybdenum oxide

Solid solutions of Ce1-xNdxO2-x/2 (0.05 <= x <= 0.2) and (Ce1-xNdx)(0.95)MO0.05O2-delta (0.05 <= x <= 0.2) have been synthesized by a modified sol-gel method. Both materials have very low content of SiO2 (similar to 27 ppm). Their structures and ionic conductivities were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and electrochemical impedance spectroscopy (M). The XRD patterns indicate that these materials are single phases with a cubic fluorite structure. The powders calcined at 300 degrees C with a crystal size of 5.7 nm have good sinterability, and the relative density could reach above 96% after being sintered at 1450 degrees C. With the addition Of MoO3, the sintering temperature could be decreased to 1250 degrees C. Impedance spectroscopy measurement in the temperature range of 250-800 degrees C indicates that a sharp increase of conductivity is observed when a small amount of Nd2O3 is added into ceria, of which Ce0.85Nd0.15O1.925 (15NDC) shows the highest conductivity. With the addition of a small amount Of MoO3, the grain boundary conductivity of 15NDC at 600 degrees C increases from 2.56 S m(-1) to 5.62 S m(-1).

Atomic force microscopy imaging of molybdenum oxide film electrodeposited on a carbon electrode

Non-stoichiometric mixed-valent molybdenum(VI, V) oxide film was grown on carbon substrates by the electrodeposition method. Responses of the prepared molybdenum oxide thin films to potential and to different solution acidities were studied by cyclic voltammetry, and the corresponding morphological changes of the film were monitored by atomic force microscopy (AFM). AFM images of the molybdenum oxide film show that the characteristic domed structure on the film surface increased during the transition from the oxidized state to the reduced state without signification change in the KMS surface roughness value. Furthermore, AFM studies show that the solution acidity has great effect on the morphology of the films, and the films undergo a homogenizing process with increasing pH of the solutions. (C) 1999 Elsevier Science S.A. All rights reserved.

ELECTROCATALYTIC PROPERTIES OF MIXED-VALENCE MOLYBDENUM OXIDE THIN-FILM MODIFIED MICROELECTRODES

A compact blue conducting mixed-valence Mo (VI,V) oxide film was grown on the surface of a carbon fibre (CF) microelectrode by cycling the potential between +0.20 and similar to 0.70 V SCE in freshly prepared Na2MoO4 solution in H2SO4 (pH 2). The thicknes

Electrochemical behavior of redox species at carbon fibre microdisk array electrode modified with mixed-valent molybdenum(VI, V) oxide

In this study, electrode responses to a large number of electroactive species with different standard potentials at the molybdenum oxide-modified carbon fibre microdisk array (CFMA) electrode were investigated. The results demonstrated that the electrochemical behavior for those redox species with formal potentials more positive than similar to 0.0 V at the molybdenum oxide-modified CFMA electrode were affected by the range and direction of the potential scan, which were different from that at a bare CFMA electrode. If the lower limit of the potential scan was more positive than the reduction potential of the molybdenum oxide film, neither the oxidation nor the reduction peaks of the redox species tested could be observed. This indicates that electron transfer between the molybdenum oxide film on the electrode and the electroactive species in solution is blocked due to the existence of a high resistance between the film and electrolyte in these potential ranges. If the lower limit of the potential scan was more negative than the reduction potential of the molybdenum oxide film (similar to - 0.6 V), the oxidation peaks of these species occurred at the potentials near their formal potentials. In addition, the electrochemical behavior of these redox species at the molybdenum oxide-modified CFMA electrode showed a diffusionless electron transfer process. On the other hand, the redox species with formal potentials more negative than similar to - 0.2 V showed similar reversible voltammetric behaviors at both the molybdenum oxide-modified CFMA electrode and the bare electrode. This can be explained by the structure changes of the film before and after reduction of the film. In addition we also observed that the peak currents of some redox species at the modified electrode were much larger than those at a bare electrode under the same conditions, which has been explained by the interaction between these redox species and the reduction state of the molybdenum oxide film. (C) 2000 Elsevier Science Ltd. All rights reserved.

Improved performances of organic light-emitting diodes with metal oxide as anode buffer

We demonstrate extremely stable and highly efficient organic light-emitting diodes (OLEDs) based on molybdenum oxide (MoO3) as a buffer layer on indium tin oxide (ITO). The significant features of MoO3 as a buffer layer are that the OLEDs show low operational voltage, high electroluminescence (EL) efficiency and good stability in a wide range of MoO3 thickness. A green OLED with structure of ITO/MoO3/N,N-'-di(naphthalene-1-yl)-N,N-'-diphenyl-benzidene (NPB)/NPB: tris(8-hydroxyquinoline) aluminum (Alq(3)):10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T)/Alq(3)/LiF/Al shows a long lifetime of over 50 000 h at 100 cd/m(2) initial luminance, and the power efficiency reaches 15 lm/W. The turn-on voltage is 2.4 V, and the operational voltage at 1000 cd/m(2) luminance is only 6.9 V. The significant enhancement of the EL performance is attributed to the improvement of hole injection and interface stability at anode.

Electrochemical preparation of microelectrodes modified with non-stoichiometric mixed-valent molybdenum oxides

A compact non-stoichiometric molybdenum (VI, V) oxide of blue film was grown on carbon fiber (CF) microelectrode surface be cycling the potential between + 0.2V and - 0.70V in a freshly prepared Na2MoO4 solution containing 5 x 10(-3) mol/L H2SO4. The quantity-of the oxide is controlled by the charge passing the electrode. The electrochemical pretreatment of CF microelectrode not only mises the deposition velocity of molybdenum oxide on CF surface, but also improves greatly the cyclic voltammetric behavior of the molybdenum oxide film prior to the electrodeposition. The cathodic processes are believed to yield the hydrogen molybdenum oxide bronzes HxMoO3(0 < x < 2), or substoichiometric lower molybdenum oxides with the formula MoO3-y(0 < y < 1). The anodic response results from the reversible oxidation of molybdenum bronze/Mo(V) centers [or perhaps Mo(IV) in more reduced coatings], to Mo(VI). Further information was gained about the chemical composition and valent state of Mo from XPS and SEM.

Tandem organic light-emitting diodes with an effective charge-generation connection structure

The tandem organic light-emitting diodes (OLEDs) with an effective charge-generation connection structure of Mg-doped tris(8-hydroxyquinoline) aluminum (Alq(3))/Molybdenum oxide (MoO3)-doped 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) were presented. At a current density of 50 mA/cm(2), the current efficiency of the tandem OLED with two standard NPB/Alq(3) emitting units is 4.2 cd/A, which is 1.7 times greater than that of the single EL device. The tandem OLED with the similar connection structure of Mg-doped PTCDA/MoO3-doped PTCDA was also fabricated and the influences of the different connection units on the current efficiency of the tandem OLED were discussed as well.

Al/WO3/Au as the interconnecting layer for efficient tandem white organic light-emitting diodes

White light emission from tandem organic light-emitting diodes consisting of blue and red light units separated by a transparent interconnecting layer of Al/WO3/Au has been realized. The devices have a structure of indium-tin-oxide (ITO)/molybdenum oxide (MoO3) (8 nm)/N, N'-di(naphthalene-1-yl)-N, N'-diphenyl-benzidine (NPB)(100 nm)/p-bis(p-N, N-diphenyl-aminostyryl) benzene) (DSA-ph): 2-methyl-9,10-di(2-naphthyl) anthracene (MADN)(40 nm)/tris(8-hydroxylquinoline) aluminium (Alq(3)) (10 nm)/LiF(1 nm)/Al(2 nm)/WO3(3 nm)/Au(16 nm)/MoO3(5 nm)/NPB(60 nm)/Alq(3): 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)(30 nm)/Alq3(30 nm)/LiF(1 nm)/Al(150 nm).

Unidirectional current flow of reversible redox couples on a MoO3 film-modified microelectrode

In this paper, we have investigated the reactivity of the molybdenum oxide film toward some standard redox systems (e.g., ferrocene (Fc) and its derivatives) and observed a few interesting phenomena. The results demonstrate that the electrochemical behaviour of Fc and its derivatives at the oxide-modified carbon fiber (CF) microelectrode differs from that at a bare CF microelectrode, The conductivity of the molybdenum oxide film is seriously affected by the range and the direction of the potential scan, which influences the electrochemical behaviour of these redox systems at the film electrode. If the cycling potential is more positive than the reduction potential of the molybdenum oxide film, the reduction and oxidation peak currents of Fc and its derivatives could not be observed. The result indicates that the molybdenum oxide film on a microelectrode surface cannot transfer electrons between the surface of the electrode and Fc or its derivatives due to the existence of a high resistance between the interface in these potential ranges. On the other hand, if the lower limit of the scan potential was extended to a potential more negative than the reduction peak potential of the film, the oxidation peak of Fc or its derivatives appeared at about the potential relative to E-0 of Fc or its derivatives on the bare electrode, and the peak current is proportional to the concentration of these couples in the electrolyte. To our surprise, the peak height on the modified electrode is much larger than that on the bare CF microelectrode under the same conditions in the range of low concentration of these couples, and the oxidation peak potential of these couples is more negative than that on the bare CF microelectrode. On the basis of the experimental observation, we propose that these redox couples may undergo an interaction with the reduction state of the molybdenum oxide film. The new phenomena that we observed have been explained by using this interaction. (C) 1997 Elsevier Science S.A.

STUDIES ON DEFECT STRUCTURE AND CATALYTIC PROPERTIES OF SN-MO OXIDES

The present work is devoted to the studies on relationship of structure and activity of Sn-Mo oxides by using XRD, ESR, IR, XPS, TEM and SEM. Eight samples with Mo/(Mo + Sn) rations: 0.0, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9, 1.0 were prepared. On the basis of structure characterization, Sn-Mo oxides can be divided into three groups: Catalysts I with Mo/(Mo + So) less-than-or-equal-to 0.2, Catalysts II with 0.2 < Mo/(Mo + Sn) < 0.8, and catalysts III with Mo/(Mo + Sn) greater-than-or-equal-to 0.8. The solid solution of Mo5+ in tin oxide was formed and the cation vacancy was formed in catalysts I. The solid solution of Sn4+ in molybdenum oxide was formed in catalysts III. The lattice oxygen in catalysts III has higher mobility and reactivity than that in catalysts I. The catalysts III showed higher activity but lower selectivity than that of catalysts I.

高温实验中重金属钼在硅酸盐熔体中的含量研究

This dissertation discusses current status of high temperature and high pressure and focuses on analyzing systematically the solubility of heavy metals in the silicate magma in HTHP experiments. The high temperature study on the content of heavy metal molybdenum in the silicate melts in this dissertation, which is granted, based on the geology mineralization model and the theory of HTHP experiments and combined with mineralization grade and geochemical nature of Mo, discusses the difference of mineralization between mantle plume and aqueous fluids and comes to the conclusions, which are as follows: (1) The content of Mo in the silicate melts is much greater than Mo mineralization grade. The molybdenum ore has the exploitation value when the industrial grade is higher than 0.06%. Mo content in different silicate melts varies because of the concentration of SiO2, that is, Mo content in the granodiorite is greater. (2) The content of Mo, which varies with reaction time, arises first and drops down in the alkali basalt melts, while variation is not too obvious in the granodiorite melts on the whole. (3) According to the picture of sample, the conclusion is not reached very well on some issues, such as the volatility and characteristic of molybdenum oxide and dependence on the geology environment.

Catalytic decomposition of hydrazine over supported molybdenum nitride catalysts in a monopropellant thruster

The catalytic decomposition of hydrazine over a series of MoNx/gamma-Al2O3 catalysts with different Mo loadings was investigated in a monopropellant thruster (10 N). When the Mo loading is equal to or higher than the monolayer coverage of MoO3 on gamma-Al2O3, the catalytic performance of the supported molybdenum nitride catalyst is close to that of the conventionally used Ir/gamma-Al2O3 catalyst. The MoNx/gamma-Al2O3 catalyst with a loading of about 23wt% Mo (1.5 monolayers) shows the highest activity for hydrazine decomposition. There is an activation process for the MoNx/gamma-Al2O3 catalysts at the early stage of hydrazine decomposition, which is probably due to the reduction of the oxide layer formed in the passivation procedure.

Morphology-controllable synthesis and characterization of single-crystal molybdenum trioxide

Molybdenum trioxide nanobelts and prism-like particles with good crystallinity and high surface areas have been prepared by a facile hydrothermal method, and the morphology could be controlled by using different inorganic salts, such as KNO3, Ca(NO3)(2), La(NO3)(3), etc. The possible growth mechanism of molybdenum trioxide prism-like particles is discussed on the basis of the presence of HI and the modification of metal cations. The as-prepared nanomaterials are characterized by means of powder X-ray diffraction (PXRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and ultraviolet and visible spectroscopy (UV-vis). TEM and HRTEM micrographs show that the molybdenum trioxide nanobelts and prism-like particles have a relatively high degree of crystallinity and uniformity. BET specific surface areas of the as-prepared molybdenum trioxide nanocrystals are 67-79 m(2)g(-1). XPS analysis indicates that the hexavalent molybdenum is predominant in the nanocrystals. UV-vis spectra reveal that the direct band gap energy of the annealed molybdenum trioxide prism-like particles shows a pronounced blue shift compared to that of bulk MoO3 powder.

An organic-inorganic vanadium oxide with one-dimensional ladder-type structure: hydrothermal synthesis, structure and characterization of [V4O10(o-phen)(2)]

A novel organic-inorganic hybrid vanadium oxide [V4O10(o-phen)(2)], involving all vanadium atoms present in +5 oxidation, has been hydrothermally synthesized and characterized by elemental analysis, IR, UV-vis, ESR, XPS spectra and TG-DTA thermal analysis. The single-crystal X-ray diffraction shows that the red-brown crystal is formed in the triclinic system, space group P (1) over bar, a = 9.782(2), b = 6.5124(14), c = 19.765(4) Angstrom, alpha = 89.94(2)degrees, beta = 100.66(2)degrees, gamma = 89.86(2)degrees. The title compound exhibits an infinite one-dimensional ladder-type tetravanadate skeleton with organonitrogen donors of o-phenanthroline ligands coordinated directly to the vanadium oxide framework.