A p-Silicon/Zn-tetra pyridyl-porphyrin (ZnTPyP) heterojunctionwas fabricated by forming a ZnTPyP layer on a p-type Si single crystal substrate using a conventional thermal evaporation technique. Complex impedance measurements of the Al/p-Si/ZnTPyP/Au heterojunction were carried out at applied AC-voltage range from 0.2 V to 1 V, temperature range from 303 K to 353 K and over the frequency range from 100HZ to 2 MHz. Impedance spectra of the heterojunction under the standard illumination ranged from 0 to 40 mW/cm(2) were reported and analysed. (C) 2017 Elsevier B.V. All rights reserved.

Polyaniline-(PANI)-poly (methyl methacrylate) (PMMA) blend was used to fabricate the Schottky device: Al/ PANI-PMMA /Au. Current density-voltage (J-V) capacitance-voltage (C-V), and complex impedance measurements were used to evaluate the junction parameters of the devices. The photovoltaic parameters of the cells are estimated from the analysis of the current-voltage characteristics under illumination.

A composite of polyaniline (PANI) containing iron oxides (Fe3O4) with nanometer size was prepared by a chemical method. The electrical properties of (PANI-Fe3O4) sandwich structure using ohmic gold and blocking aluminium electrodes were studied. The current density - voltage (J-V) characteristics for the device resemble the typical dark current versus applied voltage characteristic for conventional Schottky diode. Electronic parameters have been calculated using J-V and capacitance-voltage (C-V) measurements.

The electrical and photoelectrical properties of oxygen doped films of nickel phthalocyanine photovoltaic cells have been studied using ohmic gold and blocking indium electrodes. DC conduction processes identified depend both on the polarity and on the electric field strength. Under forward bias (gold electrode positive), conductivity is ascribed to Schottky diode behaviour at lower fields and by space- charge-limited conductivity controlled by an exponential trap distribution at higher fields. Under reverse bias, the conduction process is interpreted in terms of an electrode-limited to a bulk limited transition. The photovoltaic parameters of the cells are evaluated from the current-voltage characteristics under illumination. Space charge concentrations and barrier heights are estimated from the capacitance-voltage measurements both in dark and under constant illumination. From the action spectra of the photocurrent it is concluded that the carrier generation process is wavelength independent.

Capacitance measurements of oxygen doped films of alpha or beta iron phthalocyanine particles dispersed in a binder polymer polycarbonate (MK), with mixed (Al, Au) electrodes are studied. The capacitance of the cells changes in accordance with the morphological forms. A complete study of the space charge density as a function of temperature is carried out. The results obtained are in accordance with the model proposed for the dopant, oxygen. The low conductivity of the iron phthalocyanine is due in large part to deep trap carriers presented in this phase.

The electrical and photoelectrical properties of photovoltaic cells, made by dispersing particles of copper phthalocyanine (CuPc) in a binder polymer (polycarbonate MK) and sandwiching between gold and indium electrodes, have been studied. A complete study of the current as a function of voltage and temperature is carried out. At low voltages, the current in the forward direction varies exponentially with voltage. At higher voltages, two separate regions of ohmic and space charge limited conduction (SCLC) are observed. The latter process is controlled by an exponential distribution of traps above the valence band edge Analysis of the results enables the. determination of the important trapping parameters. Reverse characteristics are interpreted in terms of both the Poole-Frenkel and Schottky effects. Barrier heights and widths are determined as a function of applied voltage. The photovoltaic parameters of the cells are determined from the analysis of the current -voltage characteristics under illumination. Trap density and Schottky barrier built in potential are estimated from capacitance-voltage measurements.

The dielectric constant and the dielectric loss of thin films of metal-free phthalocyanine dispersed in polycarbonate using ohmic gold electrodes are investigated in the frequency range 20-10(5) Hz and within the temperature range 300-388 K. The frequency dependence of the impedance spectra plotted in the complex plane shows semicircles. The Cole-Cole diagrams have been used to determine the molecular relaxation time, tau, The temperature dependence of tau is expressed by thermally activated process. The AC conductivity sigma(AC)(omega) is found to vary as omega(s) with the index s less than or equal to 1, indicating a dominant hopping process at low temperatures. From the temperature dependence of AC conductivity, free carrier conduction with mean activation energy of 0.33 eV is observed at higher temperatures. Capacitance and loss tangent are found to decrease with increasing frequency and increase with increasing temperature. Such characteristics are found to be in good qualitative agreement with existing equivalent circuit model assuming ohmic contacts. (C) 1999 Elsevier Science B.V. All rights reserved.

Current density-voltage characteristics have been obtained from thin films of cobalt phthalocyanine when sandwiched between ohmic gold contacts. Results showed ohmic conduction in the lower voltage range and space-charge limited conduction controlled by an exponential distribution of traps above the valance band edge for a higher voltage section. Analyses of the results yielded the following values: the hole mobility μ ≈ 4.4 × 10−6 m2 V−1 S−1, the room temperature hole concentration p ≈ 2.9 × 1014 m−3, concentration of traps per unit energy range at the valence band edge P ≈ 1.3 × 1043 J−1 m−3, the temperature parameter Tt of trapping distribution 1288 K, and the total trapping concentration Nt ≈ 2.3 × 1023 m−3. The dependence of capacitance C on temperature shows that C is temperature insensitive, below 300 K, above which there is a rapid increase with increasing temperature and finally at about 400 K, C saturates. Such characteristics were found to be in good qualitative agreement with the existing equivalent circuit models assuming ohmic contacts.

The electrical properties of oxygen doped thin films of cobalt phthalocyanine sandwich structures have been studied using ohmic gold and blocking aluminium electrodes. The current density-voltage characteristics under forward bias (gold electrode positive) were found to exhibit three different regions. At low voltages the devices (Al/CoPc/Au) showed Schottky diode behaviour. The model of Cheung and Cheung was used to derive diode parameters. At higher voltage regions the results showed ohmic conduction and above a threshold voltage a power-law dependence of current density on applied voltage was observed. The latter was ascribed to space-charge-limited conduction controlled by exponential distribution of traps above the valence band edge. The hole trapping parameters were evaluated. Under reverse bias, the conduction processes were interpreted in terms of both the Poole-Frenkel and Schottky effects. Barrier heights emphasise the importance of oxygen distribution in CoPc and the existence of interfacial oxide layers in the determination of the electrical characteristics of CoPc based devices.

The electrical conductivity of cobalt phthalocyanine thin film sandwich structures using ohmic gold and blocking aluminium electrodes has been measured both after exposure to oxygen for 30 days and after annealing at temperatures up to 423 K. Current density-voltage characteristics under forward bias (gold electrode positive) were found to be due to space-charge-limited conduction controlled by an exponential distribution of traps at lower voltage sections and by a discrete trap level at higher voltage regions. Under reverse bias, the conduction process was interpreted in terms of an electrode-limited to a bulk-limited transition, from Schottky emission to the Poole-Frenkel effect. The effect of annealing resulted in similar behaviour and was found to reduce current density due to oxygen desorption.

Current density-voltage characteristics have been obtained from thin films of nickel phthalocyanine particles dispersed in a polymer binder when sandwiched between ohmic gold contacts. Results showed ohmic conduction in the lower voltage range and space-charged limited conduction controlled by an exponential distribution of traps above the valence band edge for higher voltage sections. Analyses of the results yielded the following values: hole mobility, μ ≈ 1.0 × 10 5m2V1s−1; room temperature hole concentration, po ≈ 1.2 × 1014m−3; concentration of traps per unit energy range at the valence band edge, Po ≈ 2.2 × 1044 J−1m−3; temperature parameter of trapping distribution, T1 ≈ 820 K; total trapping concentration, Nu(e) ≈ 1.8 × 1024m−3.

Current density-voltage characteristics and thermally stimulated currents have been obtained from thin films of β-nickel phthalocyanine particles dispersed in a polymer binder, when sandwiched between ohmic gold and blocking aluminium electrodes. At low voltages, the current in the forward direction varies exponentially with voltage. At higher voltages, two separate regions of space-charge limited current conduction under forward bias were observed. Under reverse bias, the conduction process at low voltages is determined by Schottky emission over a potential barrier of approximate height, 0·89 eV and thickness 65 nm. At higher voltages, the Poole-Frenkel effect was observed. The activation energy of the hole trapping level determined from the thermally stimulated current measurements has an electric field dependence. The results are interpreted in terms of the Poole-Frenkel effect.

The dielectric constant and the dielectric loss of potassium acetylacetonate, K(acac), are measured as a function of both temperature and frequency. A peak value is obtained at the a critical temperature T(c) = 313 K. X-ray analysis revealed that at T(c), K(acac) undergoes phase transition from orthorhombic to triclinic structure. The Cole-Cole diagrams have been used to determine the molecular relaxation time-tau. The temperature dependence of tau is expressed by thermally activated process. The impedance spectra in the frequency range from 50 Hz to 500 kHz plotted in the complex plane show semicircles. The conduction mechanism, below T(c), is predominantly operating at the surface. Above T(c), the conduction is proceeding in the bulk material with contribution from the surface.

The dielectric properties of cobalt phthalocyanine are investigated in the frequency range 50-5 x 10(5) Hz and within the temperature range 293-363 K. The frequency dependence of the AC impedance could be expressed by the complex plane of the complex impedance. Analysis of the AC conductivity reveals semiconducting features based predominantly on the hopping mechanism. The relaxation time, derived from the experimental results, shows a thermally activated process.

Low-frequency oscillographic capacitance measurements are employed to characterize Schottky barrier cells made with either oxygen-doped alpha-iron phthalocyanine or beta-iron phthalocyanine dispersed in a polymer binder.The alpha-phase cell shows a Schottky barrier capacitance down to 165 K. The capacitance-voltage relationships measured at various temperatures are explained by a two-site model for the dopant, oxygen. The beta-phase cell, on the other hand, shows Schottky barrier capacitance at room temperature which upon cooling down changes to geometrical capacitance. The results of this study show that the space-charge density is comparable in both cells. The low conductivity of the beta-phase cell is attributed to deep trap carriers present in this phase.

Electrical and photoelectrical measurements are made on thin films of β-cobalt phthalocyanine particles in Schottky junction cells. The results of current density-voltage characteristics in dark at constant temperature are interpreted in terms of a space charge limited mechanism dominated by an exponential distribution of trapping levels. An analysis of the results enables the determination of the Fermi temperature of the trap distribution. The dependence of the photovoltaic parameters on pigment loading and polymer binder are investigated. Typical polymeric binders used throughout this study are polyvinylacetate (PVA) and polycarbonate (MK). The results show that the polymer has a strong effect on photocurrent generation efficiency in phthalocyanine composite type photovoltaic cell; polymers having a polar group seem desirable for improving the performance. An dünnen β-Kobalt-Phthalozyaninpartikelschichten in Schottky-übergangszellen werden elektrische und photoelektrische Messungen durchgeführt. Die Ergebnisse der Stromdichte-Spannungscharakteristik im Dunkeln bei konstanter Temperatur werden mit einem Mechanismus der Raumladungsbegrenzung, der durch eine exponentielle Verteilung der Trapniveaus beherrscht wird, interpretiert. Eine Analyse der Ergebnisse ermöglicht, die Fermitemperatur der Trapverteilung zu bestimmen. Die Abhängigkeit der Photospannungsparameter von der Pigmentbeladung und dem Polymerbinder wird untersucht. Typische polymere Binder, die durchweg für die Untersuchung benutzt werden, sind Polyvinylazetat (PVA) und Polykarbonat (MK). Die Ergebnisse zeigen, daß das Polymer einen großen Einfluß auf den Photostromgenerationswirkungsgrad in Phthalozyanin-Photospannungszellen hat; Polymere mit einer polaren Gruppe scheinen für eine Verbesserung der Leistungsparameter geeignet.

The influence of chloroacetic acid amide (AC) on the temperature-dependence of the electrical conductivity (σ), thermal expansion (αij) and specific heat ((Cp) of triglycine sulphate crystals was studied in the phase transition range (Tc=49°). The addition of isostructural AC increased the electrical conductivity, decreased the thermal expansion and changed theCp peak. The mechanism is discussed on a thermodynamic basis.

Stress relaxation was carried out on single crystals of copper and aluminium in the temperature range 78–500 K. An empirical formula for stress relaxation data is proposed to fit the experimental stress relaxation curves. The internal stress σi was determined and shown to be 0.9σ0 where σ0 is the applied stress at the beginning of the relaxation process.

AbstractThe parameters of a spherical surface barrier with refraction for the particles sputtered from Cu single crystals are computer calculated. Use is made of the method of straightforward simulation of the surface atom ejection in the field of the near‐surface block of atoms. The interactions of the atoms are described by a Morse potential.