Phenoxazine and N-phenyl-1-naphtylamine-based enamines as hole-transporting glass-forming materials

New aromatic enamines were synthesized by condensation of the commercially available phenoxazine and N-phenyl-1-naphtylamine with 2,2-diphenylacetaldehyde or 2-phenylpropionaldehyde. The materials were examined by various techniques including differential scanning calorimetry, UV and fluorescence spectrometry, electron photoemission and time of flight techniques. The electron photoemission spectra of the layers of the amorphous materials showed the ionization potentials of 5.42–5.61 eV. Hole drift mobilities in the layers of 33–50% solid solutions of the derivatives in bisphenol Z polycarbonate range from 10⁻⁵ to 3.4 × 10⁻⁴ cm²/V s at high electric fields.     

Molecular glasses possessing a phenyl-1,2,3,4-tetrahydroquinoline moiety as hole transporting materials for electrophotography

The new hole transporting materials which comprise molecules consisting of two hydrazone branches linked with flexible thiobiphenyl or thiophenyl sulphide and two hydroxyl groups containing central bridge were synthesized and investigated. These transporting materials possessing phenyl-1,2,3,4-tetrahydroquinoline moieties are low molecular glasses and allow preparing stable to crystallization layers. The ionization potentials of these compounds are ca. 5.3 eV as determined by the electron photoemission method. These low molecular glasses can be used as hole transporting materials with or, in the case of a solid substrate, without binder polymer. The hole drift mobility of the newly synthesized compounds, measured by xerographic time of flight method, exceeds 10⁻⁵ cm²/V s at an electric field of 10⁶ V/cm.     

Aniline-based bis(enamines) as new amorphous molecular charge transport materials

A series of new aniline-based bis(enamines) has been synthesized. The full characterization of their structure is presented. The thermal, optical and photoelectrical properties of the newly synthesized enamines are discussed. The reported compounds constitute materials with high thermal stability with 5% weight loss temperatures exceeding 390 °C as characterised by thermogravimetric analysis. They form glasses with the glass transition temperatures ranging from 135 to 154 °C as established by differential scanning calorimetry. Photoelectric properties of the materials were examined by electron photoemission and time of flight technique. The electron photoemission spectra of the layers revealed the ionization potentials of 5.12–5.70 eV. Room temperature hole drift mobility of one newly synthesized derivative molecularly doped in bisphenol Z polycarbonate reached 10⁻⁵ cm² V⁻¹ s⁻¹ at high electric fields.     

Diphenylamino-substituted derivatives of 9-phenylcarbazole as glass-forming hole-transporting materials for solid state dye sensitized solar cells

The synthesis and properties of glass-forming diphenylamino-substituted derivatives of 9-phenylcarbazole with methoxy groups in the different position of diphenylamino moieties are reported. A comparative study on their thermal, optical, photoelectrical and electrochemical properties is presented. The synthesized compounds exhibit high thermal stability with 5% weight loss temperatures ranging from 344 to 475 °C. The derivatives absorb electromagnetic irradiation in the range of 225–425 nm with the band gaps of 2.94–3.08 eV. The ionization energies of the synthesized compounds range from 5.04 to 5.56 eV. The lowest ionization energies and band gaps are observed for compounds containing para methoxy-substituted phenyl rings of diphenylamino moieties and for disubstituted carbazole derivatives. Charge-transporting properties of the selected compounds were tested by time-of-flight technique. Hole drift mobilities in the amorphous layers of the materials reach 10⁻³ cm²/V s at high electric fields. The derivatives were tested as hole transport materials in solid-state dye sensitized solar cells and showed conversion efficiency up to 0.54%.     

Triindolylmethane-based high triplet energy glass-forming electroactive molecular materials

A series of new triindolylmethane-based compounds including those containing reactive functional groups were synthesized by the tandem addition–elimination–(Michael) addition reaction from 1H-indole and 1H-indole-3-carbaldehyde. The thermal, optical, photophysical and photoelectrical properties of the synthesized compounds were studied. The synthesized compounds exhibit moderate thermal stability with 5% weight loss temperatures ranging from 245 to 310 °C and form glasses with glass transition temperatures in the range of 98–123 °C. The ionization potentials of the synthesized compounds measured by the electron photoemission in air technique range from 5.67 to 5.80 eV. The solutions of the synthesized compounds show relatively high triplet energies in the range from 2.97 to 2.99 eV.     

Synthesis of new hole-transporting molecular glass with pendant carbazolyl moieties

The synthesis and properties of amorphous hole-transporting 4,4′-bis[11-carbazol-9-yl)-6,8,10-tri(carbazol-9-methyl)-3-hydroxy-5,7,9-trioxa-1-thia]thiobisbenzene with two end and six pendant carbazolyl moieties, separated from the main chain by CH₂ spacers, is reported. It was prepared by a multistep synthesis route from 1,6-di(carbazol-9-yl)-5-(carbazol-9-methyl)-4-oxa-2-hexanol glycidyl ether. Glass transition temperatures of intermediate and final products established by differential scanning calorimetry are reported. The hole drift mobility, measured by the time of flight technique, in this well defined molecular glass depends little on the strength of the electric field and exceeds 10⁻⁵ cm² V⁻¹ s⁻¹. The ionization potentials measured by electron photoemission method, light absorption and fluorescence spectra are closed to those reported for the other organic photoconductors containing electronically isolated carbazole moieties.     

Electrochemical methods coupled with impedance measurement for energy gap study: correlation between the energy states and charge transport properties

The energy states of poly(3-hexylthiophene) (P3HT) polymer films degraded using UV/ozone environment were studied by optical and electrochemical methods. Energy levels of highest occupied and lowest unoccupied molecular orbitals as well as localized states between them were estimated. Electrical properties of polymer films sandwiched between two metal electrodes were investigated for various trap energy distributions. Comparison of the energy states density evaluated by optical/electrochemical methods and estimated from the current-voltage characteristics was carried out to discuss suitability of space-charge limited electrical conduction models for semiconducting polymers.     

Space charge limited current–voltage characteristics of organic semiconductor diode fabricated at various gravity conditions

In this paper, temperature-dependent current–voltage (I–V) characteristics of poly-N-epoxipropyl carbazole (PEPC) are evaluated. The PEPC is doped with anthracene (An) and deposited on nickel (Ni) substrate with a centrifugal machine. The films are grown at room temperature but at varying gravity conditions, such as 1g, 123g, 277g and 1107g, where g is acceleration due to gravity. It is demonstrated that the space charge created by the trapped charges controls the device's characteristics. Thus, by employing trapped space charge limited current model, charge transport parameters are estimated and discussed as a function of ambient temperatures. It is learned that the trap factor, free carrier density, effective mobility and trap density are quasi-linear functions of temperatures. It is shown that devices fabricated at 277g exhibit superior electrical properties compared to 1g, 123g and 1107g devices. It has been demonstrated that an organic semiconductor device performance could be enhanced by optimizing its fabrication parameters.     

Cross-linkable aromatic amines as materials for insoluble hole-transporting layers in light-emitting devices

A series of cross-linkable aromatic amines has been synthesized by the multi-step synthetic rout. Full characterization of their structure by ¹H NMR-, IR- and mass spectrometry is presented. The synthesized materials were examined by various techniques including differential scanning calorimetry, thermogravimetry, UV and electron photoemission spectrometry. The electron photoemission spectra of the layers showed their ionisation potentials of 5.1–5.2 eV. One of the derivatives was used for the preparation of insoluble hole-transporting layers by photoinduced polymerization. The layers obtained were tested in multilayer light-emitting diodes. The device-containing hole-transporting layer of PEDOT/cross-linked network exhibited the best overall performance with a turn-on voltage of 5 V, a maximum photometric efficiency of 2.8 cd/A and a maximum brightness of ca. 5600 cd/m².     

Dual-plasma ion process for surface treatment of insulators

Surface treatment of insulator materials has growing needs recently. However, accumulation of charges on the insulator surface limits the applicability of plasma methods for the insulator processing. A radio-frequency-bias method is a good choice but it still has a problem coming from the oscillating sheath potential. In the present study, we are proposing the dual-plasma ion process, a new plasma process that enables for insulator samples to be treated by an energy-controlled, dc ion beam without surface charging. The concept and results of the proof-of-principle experiment are given.     

Effects of graphite on Zn-Sb alloys as anode materials for lithium-ion batteries

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TiO2-coated SnO2 hollow spheres as anode materials for lithium ion batteries

TiO2-coated SnO2(TCS) hollow spheres,which are new anode materials for lithium ion(Li-ion) batteries,were prepared and characterized with X-ray diffraction(XRD) ,scanning electron microscopy(SEM) ,transmission electron microscopy(TEM) ,cyclic voltammetry(CV) ,and galvanostatic charge/discharge tests.The results obtained from XRD,SEM,and TEM show that TiO2 can be uniformly coated on the surface of SnO2 hollow spheres with the assistance of anionic surfactant.The cyclic voltammograms indicate that both TiO2 a...