Glass Anode Research Articles

Electroluminescence properties of poly[2-(2′-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene]/tris(8-hydroxyquinoline)aluminum two-layer devices

Two-layer electroluminescing (EL) devices were constructed employing poly[2-(2′-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) and tris(8-hydroxyquinoline)aluminum (Alq 3). On the indium–tin oxide (ITO) glass anode MEH-PPV layer was first spin-coated, on which the Alq 3 layer and the aluminum (Al) anode were vapor-deposited sequentially. When the thickness of Alq 3 was less than that of MEH-PPV, the device showed the EL emission spectrum originated only from the latter. The devices, however, exhibited the combined EL spectra of MEH-PPV and Alq 3 when latter's layer was thicker than the former's layer. The external efficiency for light emission by the double-layer devices was improved by close to two orders of magnitude when compared with efficiency of the MEH-PPV single-layer device, when the thickness of the Alq 3 layer was slightly thicker than that of the MEH-PPV layer. The maximum efficiency obtained was about 0.02%. Current flow in the two-layer devices was limited effectively by the Alq 3 layer and it decreased steadily as the thickness of the Alq 3 layer was increased. The results were discussed on the basis of improved exciton formation resulting from accelerated and balanced carrier transport.

Luminescence properties of poly[1,4-phenylenevinylene-co-(2,3,5,6-tetramethyl-1,4-phenylenevinylene)] - Improved EL efficiency through partial disruption of main chainπ-conjugation by substituents

Two copolymers of poly(p-phenylenevinylene) (PPV) containing low levels (0.8 and 3.6 mole %) of the 2,3,5,6-tetramethyl-1,4-phenylenevinylene (TMPV) units were prepared via the sulfonium salt precursor route. The luminescence properties of the two copolymers were studied in detail mainly for photoluminescence (PL) and electroluminescence (EL) characteristics in comparison with those of PPV itself. Inclusion of low levels of TMPV units improves EL efficiency by more than 10 times when a single layer device was constructed using ITO coated glass anode and aluminum metal cathode. This was explained by the possible partial disruption of main chain π-conjugation by the TMPV units which force its phenylene or vinylene structure to twist out of the coplanar structure in order to avoid of the steric repulsion between the methyl and vinyl protons in the TMPV units. The UV-vis, PL and EL spectra of the copolymers support this supposition.

Tunable electroluminescence from ionomers doped with cationic lumophores

We report a novel electroluminescent device using an ionic polymer as the host for ionically functionalized fluorescent dyes. Blue electroluminescence is observed from the laser dye 5-Phenyl-2-(4-pyridyl)oxazole (PPyO), methyl tosylate salt immobilized in the fluoropolymer Nafion which is spin-coated onto a conducting indium tin oxide (ITO) glass anode. The same ionomers are also used to blend small amounts of the conducting polymer poly( o-toluidine) to form an efficient hole injecting layer between the ITO and emitter layer. Electron injecting layers are constructed with 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole in Nafion and are spincoated on top of the emitter layer. The cathode is an evaporated aluminum layer on top of the electron injecting layer. Devices operate in forward and reverse bias and under AC fields with light emission corresponding closely to device photoluminescence spectra.

Orientation-controlled organic electroluminescence of p-sexiphenyl films

A multilayered electroluminescent device was constructed with epitaxially oriented films of p-sexiphenyl with its molecular axis lying or standing next to the substrate surface. The films with the lying and standing orientations were prepared by vapor deposition onto the KCl (001) surface kept at 20 and 150 °C, respectively. After successive depositions of electron-transport layer and Al cathode, the films were removed from the KCl substrate and transferred on an indium tin oxide coated glass anode. The cell with lying molecules emitted a higher electroluminescence with a narrowed spectrum at remarkably low driving voltages, as compared to one with standing molecules. This electroluminescent behaviors depend upon anisotropic distribution of the polarized emission light as well as efficiency of the carrier transport in the ordered molecular arrays with different orientation modes.

Structure and electronic properties of polythiophene and poly(3‐alkylthiophene) films electropolymerized on indium tin oxide (ITO) glass at elevated potentials

AbstractHomogeneous and flexible films of polythiophene are known to be difficult to obtain electrochemically on indium tin oxide (ITO) glass electrodes using normal 1,6–1,7 V applied voltage. The situation is greatly improved by using higher voltage. 0,1–10 μm thick films of polythiophene (PT) and various poly(3‐alkylthiophene)s (P3AT's) (alkyl = methyl (P3MT), hexyl (P3HT) and octyl (P3OT)) were electropolymerized on ITO‐covered glass anodes under an applied voltage of 8 V vs. an Ag/AgCl reference electrode. In this paper we report upon the properties of these films compared to their chemically and at low‐voltage electrochemically polymerized equivalents. Generally, the films have all the properties known for PT and P3AT's. Characteristics such as thermo‐ and solvatochromism, conductivity and electronic band structure as studied by ultraviolet photoemission spectroscopy and optical absorption were comparable to the properties shown by the reference samples. However, the structure of high‐voltage films differs considerably from those reported for chemically polymerized samples. The high‐voltage films contain a higher amorphous fraction, and the polymer is more cross‐linked and branched.

A boron-nitrogen conducting polymer

A boron-nitrogen polymer has been synthesized from both the electrochemical and the chemical polymerization of the monomer borazine, B 3N 3H 6. Electrochemical oxidation has been carried out in an electrolyte of LiAsF 6 and CuCl 2 dissolved in nitrobenzene. Polymerization to produce thin films on an indium tin oxide (ITO) conducting glass anode occurs when a potential greater than 6.5V is passed between the ITO electrode and a platinum counterelectrode. Conductivities for the p-doped film of ∼10 S cm −1 were readily obtained. Chemical oxidation of borazine using a Lewis Acid catalyst was carried out at room temperature to produce a pristine, white insulating polyborazine powder. Infrared spectra indicate B-H, N-H and B-N ring stretches as expected for polyborazine. In addition to the new electronic materials properties, undoped polyborazine is a precursor to the important ceramic boron nitride.

Novel conducting Langmuir-Blodgett films based on 2-octyloxy-5, 6,11,12-tetrathiotetracene-preparation methods and physical properties

Novel electrically-conducting Langmuir-Blodgett (LB) films containing the new donor compound 2- n-octyloxy-5,6,11,12-tetrathiotetracene ( 1) are described. In order to prepare conducting films, several oxidation (doping) methods were applied: (a) exposure of LB films of 1 to iodine vapour; (b) immersion of LB films in aqeous KI 3 solution; (c) anodic oxidation of LB films deposited onto indium tin oxide (ITO) glass; (d) spreading of 1 on an aqueous KI 3 solution followed by LB-type deposition; (e) spreading of 1 on an aqueous electrolyte solution followed by LB-type deposition onto a live ITO glass anode. Optical, electrical and structural studies of the oxidized LB films indicate that the physical properties are strongly dependent on the preparation method applied. Conductivity values vary between 10 −4 and 10 −2 S cm −1. The structures vary between well ordered and high disordered.

Time resolution of a large area planar spark counter

A planar spark counter of size 1.0 m × 0.1 m has been developed and tested. The constituent elements are a semiconductive glass anode and a window float-cast glass cathode coated by vacuum-deposited copper. The distance between electrodes is 200 μm. A single counter time resolution of 61 ps was achieved with cosmic rays.

The electrophoresis of thin film CdS/Cu 2S solar cells

The preparation of pinhole-free thin film CdS solar cells by evaporation has always been a problem. Electrophoresis from a CdS sol offers an alternative technique. Provided the particle size is small enough, pinhole-free films 1–2 μm thick can be prepared on large-area substrates. Here we report on electrophoretic deposition on metal, ion-plated plastic and conducting semiconductor oxide on glass anodes. Solar cells were fabricated by adding a Cu 2S layer by evaporation or by the well-known copper ion dip technique. Efficiencies up to 5% were achieved without an antireflection coating. Large-area films of CdS were fabricated and a 125 cm length of stainless steel foil was coated continuously to demonstrate that scaling up to mass production is feasible. The resistivity of the films was too high and never fell below 10 3 Ω cm. More work is needed on the annealing and doping of the films to see whether this resistance can be lowered by one or two orders of magnitude so that efficient large-area solar cells can be produced.

The modernization and improvement of the BNL short separators

Two high voltage separators (10 and 15 cm gaps) have been designed, constructed, and tested for use in the new LESB II experimental beam line. Both separators have been tested to 800 kV (limited by power supply capability). The 10 cm gap separator is of the conventional heated glass-cathode, steel-anode design. The 15 cm gap separator has a glass cathode and glass anode. This separator has been conditioned above 780 kV in hard vacuum (10 −6 torr range). In order to attain and reliably maintain the high voltages necessary for testing the separator, the power supplies, cable terminations, feedthroughs, high voltage bushings, standoffs, and surge resistors have all been modified. These modifications and the final test results are discussed in detail.