Electrochromic iridium oxide thin films were deposited by spray pyrolysis technique onto indium-doped tin oxide (ITO) coated glass substrates using iridium chloride as an aqueous solution.The influence of the substrate temperature, the deposition period of time and the solution molarity have been investigated as related to the film's electrochromic (EC) performance.The electrochromic properties of the films were investigated in a (0.5M H 2 SO 4 ) aqueous electrolytic solution using cyclic voltammetry (CV).The transmittance has been measured over the spectral wavelength range between 300 and 2400 nm.The substrate temperature (T sub ), the deposition period of time, the solution molarity and the colouration and bleaching potentials were optimized and found to be 400 o C, 10 min, 0.02 M, ±0.8 V, respectively.The films have acquired a maximum transmittance solar modulation ΔT s and a maximum visible modulation ΔTv at 630 nm optimal optical modulation.The iridium oxide thin films have demonstrated a pronounced anodic electrochromic behavior owing to Ir +4 Ir +3 intervalance charge transitions.

Heterojunctions of n-ZnSe/p-H2Pc have been fabricated by thermal evaporation technique of zinc selenide and metal-free phthalocyanine layers onto p-InP (100) single-crystal wafers. Rectifying properties have been obtained and capacitance-voltage behavior indicates an abrupt interface. The transverse current–voltage characteristics of H2Pc/InP, ZnSe/InP and ZnSe/H2Pc/InP junctions have been observed in the dark and under illumination. The ZnSe/H2Pc/InP junction exhibits a strong photovoltaic response with a power conversion efficiency of 1%. The photocarrier generated in H2Pc layer is separated by the steep incline of the potential near the H2Pc/ZnSe interface. Analysis of the dark J–V characteristics as a function of temperature indicates that the conduction mechanism in the forward direction has been explained by a tunneling process. The calculated activation energy of charge carriers is found to be 0.33 eV.

n-CdS/p-InP heterojunctions have been fabricated by deposition of n-CdS thin films using a spray pyrolysis technique onto p-type InP〈100〉. Current density–voltage and capacitance–voltage measurements were performed to determine the electrical properties of the structures. The forward current involves tunneling and is explained by a multi-tunneling capture-emission model. The reverse current is limited by the carrier generation process. The capacitance–voltage behavior indicates an abrupt interface with a main-band discontinuity of 0.76 eV occurs in the valence band. Effect of InP doping density on photovoltaic parameters has also been investigated at different light intensities. The devices exhibit a maximum power conversion efficiency (up to 12%) using an optimum doping density of 1×1015 cm−3.

Thin films of ZnO onto glass substrate at different substrate temperatures Ts, ranging from 180°C to 450°C, have been prepared using a spray pyrolysis process. X-ray diffraction showed that the films prepared at Ts greater than 300°C exhibit the hexagonal wurtzite structure with a preferential orientation along (002) direction. All electrical properties have been investigated for films at Ts=400°C. A relative permittivity of 9.8 is calculated from the capacitance measurements. Thermally generated electron concentration, n0=(2.8–6.7)×1010m−1, and trapping factor, θ=(8.02–18.22)×10−12 have been evaluated from the analysis of current–voltage characteristics at room temperature assuming a plausible value of carrier mobility, 1.8m2V−1s−1. The obtained values n0 and θ are correlated with the crystallite size.

Heterojunctions have been fabricated of p-type amorphous gallium arsenide (a-GaAs) thin films onto n-type silicon (n-Si) single crystals using thermal evaporation method. Current density-voltage and capacitance-voltage measurements have been performed to determine the electrical properties of the structures. Rectifying current involves tunneling and is explained by a multi-tunneling capture-emission model. The reverse current is limited by the carrier generation process. The capacitance-voltage behavior indicates an abrupt interface with a main-band discontinuity of 0.25 eV occurs in the valance band.

Lithia ceramics with three Li 2 O:Al 2 O 3 :SiO 2 molar ratios 1:1:6, 1:1:8 and 1:1:10 were prepared and vitrified. The samples obtained at optimum firing conditions were selected to study the effect of developed phases including porosity on their optical properties. Spectrophotometrical analysis and applying the CIE system for total transmission including scattering and spectral reflectance were adopted. Crystallinity was defined morphologically using scanning electron microscope (SEM). The data indicated that the structure parameters being minimum crystallite size, maximum microstrain and porosity are related to SiO 2 content. The spectral behavior depended on the nature of the glassy matrix which in turn is related to the phase compositions of the ceramic and its crystallite size. Tristimulus transmittance peak values were reduced in parallel with increases SiO 2 content. Relative brightness and chromaticity revealed similarities for bodies with larger crystallite size and minimal microstrain having the lowest and highest LAS molar ratios.

Thin films of CdS on glass substrates have been prepared by a thermal evaporation technique using a modified evaporation source under different preparation conditions. The structural features have been investigated using XRD. The current density–voltage characteristics have been investigated at room temperature with different thicknesses. The results showed ohmic conduction in the lower voltage range and space-charge limited conduction controlled by a single-discrete trapping level for a higher voltage section. Analyses of the results yielded important dependence of film thickness on both the thermally-generated electron concentration and the trapping factor. The optical parameters have been calculated. The dependence of the refractive index, n, and extinction coefficient, k, on the wavelength for a prepared sample is also reported.

Publisher Summary The electrical and photovoltaic properties of α-ZnPc thin films in Schottky junction cells have been carried out in air ambient. These cells showed rectification when α-ZnPc material was flanked between ohmic gold and blocking indium electrodes. The current density–voltage characteristics under forward bias are found to exhibit two distinct regions of ohmic and space-charge-limited conduction (SCLC). The square power dependence in SCLC indicated that current conduction is limited by a by a discrete trapping level above the valence band edge. Optimum values of power conversion efficiency ŋ of 5.5% and quantum efficiency φ of 42.5% for input light at low power density of 0.6 mWcm–2 have been obtained for monochromatic irradiation at 633 nm. The decrease in ŋ with increasing the intensity is attributed to a space charge limitation due to nonlinear resistance. Schottky-barrier parameters of the cell in the dark and under different monochromatic light intensities have been determined from the capacitance–voltagc measurements. Light intensity increased significantly the space charge density, which is a major concern as a possible limiting factor for the performance of organic photovoltaic cells.

Heterojunction cells of p-MgPc/n-Si have been fabricated by thermal evaporation of MgPc thin films onto Si〈100〉 single crystal wafers. The devices exhibit strong photovoltaic characteristics with an open–circuit voltage of 0.35 V, a short–circuit current of 3.57 mA and a power conversion efficiency of 1.05%. These parameters have been estimated at room temperature and under a monochromatic illumination of 633 nm with an input power density of 50 mW/cm2. The activation energy of the charge carriers of 0.32 eV and the cell series resistance of 2 kΩ have been evaluated from the measurements of the dark I–V characteristics. A free–carrier concentration of 2.2×1016 cm−3 and a barrier width of 75 nm have been estimated from C–V measurements. The temperature dependence of photocurrent, at constant illumination, has been also investigated.

Schottky-barrier cells of the type (Al/p-NiPc/Au) are fabricated by successive vacuum depositions of p-NiPc thin films and aluminium fingers onto an ohmic gold electrode. The electrical conductivity has been measured both after exposure to oxygen for 10 days and after annealing at temperature up to 423K. These cells showed high rectification in the oxygen-doped process. Current density–voltage characteristics under forward bias (aluminium electrode negative) are found to be due to space-charge-limited conduction controlled by a discrete trap level at lower voltage sections and by an exponential distribution of traps at higher voltage regions. Under reverse bias, the conduction processes are interpreted in terms of a transition from electrode-limited Schottky emission to the bulk-limited Poole–Frenkel effect. The effect of annealing showed similar behaviour and resulted in lowering the current density due to oxygen desorption. The linearity of the C−2–V dependence for oxygen-doped devices is associated with a homogenous distribution of the impurities inside the space-charge region and also provided evidence of uniform doping.

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.

Heterojunction cells of p-MgPc/n-Si have been fabricated by thermal evaporation of MgPc thin films onto Si(100) single crystal wafers. The devices exhibit strong photovoltaic characteristics with an open - circuit voltage of 0.35 V, a short - circuit current of 3.57 mA, a quantum efficiency of 14.72 % and a power conversion efficiency of 1.05 %. These parameters have been estimated at room temperature and under a monochromatic illumination of 633 nm with an input power density of 50 mWcm(-2). The activation energy of the charge carriers of 0.32 eV and the cell series resistance of 2k? have been evaluated from the measurements of the dark I-V characteristics. The temperature dependence of photocurrent, at constant illumination, have been also investigated.

The one-dimensional hydrodynamic theory proposed by Tate [1.21 is considered as a standard reference for describing the penetration of long rods into semi-infinite metallic targets.In this paper, a modified analytical approach using Tate's theory has been developed, wherein the penetration process is considered to consist of three phases: hydrodynamic, deformation and rigid.These phases are related to the situations of the rod front during target penetration.For each rod phase, the target penetration is described consisting of two stages: erosion and deformation.The plastic wave theory is used with the equations of motion to predict the sequence of penetration stages that associate with each rod penetration phase and represent the complete penetration process.In addition, the strength factors for both rod and target materials, respectively, are assumed not to vary during their erosion.The governing equations of the analytical approach are programmed using FORTRAN.The input data consist of rod impact velocity, length, diameter, density and Brinell hardness number as well as target density.Young's modulus and Brinell hardness number.The present results are concerned with the predictions of the produced hole diameter and penetration depth in semi-infinite targets due to their impact by long rods with high velocities.The predicted results are compared with the experimental results of other investigators: good agreement is obtained.Moreover, the program is used to discuss the influence of the different penetration parameters on penetration depth and produced hole diameter.

Four fritted glaze formulae were prepared using soda feldspar replacing potash one. Surface and interface of the applied glazes were followed through scanning electron microscopy and diffuse reflectance. The latter parameters were converted to the CIE system to get brightness. Pores formation in the interface were traced and related to composition. Degrees of crystallinity were assessed by measuring X-ray line broadening and were supplemented by group coordination traced by infrared analysis. It was found that the introduction of soda in frits reduced bubble formation and improved aesthetic components. Crystallite sizes varied with acidity of the glaze and the strain induced by glassy portions was followed The coordination of Al, B and Zr ions were verified. The extent and interrelation of these findings with calculated chemical composition and structural characteristics of the glazes were highlighted. Rapid rate of cooling reduced crystallite size, increased strain level and affected coordination sites of the ions.

Electrical and photoelectrical measurements are made at different temperatures on heterojunction photovoltaic cells fabricated by vacuum deposition of n-ZnSe thin films onto p-Si single crystals. A complete study of the current as a function of voltage and temperature is carried out in order to gain fundamental information on trap depth, trap distribution and position of the Fermi level. The results are consistent with space-charge-limited conduction due to an exponentially decreasing distribution of traps. At low voltages, the dark current in the forward direction varies exponentially with voltage. Under reverse bias, the conduction process is interpreted in terms of a transition from electrode-limited Schottky emission to the bulk-limited Poole - Frenkel effect. The values of thermal activation energy for photoconduction and effective density of conducting states are determined and found to be 0.22 eV and , respectively. These values are estimated from the dependence of photocurrent on temperature at constant illumination with an input power density of 50 mW .

The dielectric constant and the dielectric loss of polycarbonate are investigated in the frequency range 30-105 Hz and at temperature from 297 to 365 K. The frequency dependence of the impedance spectra plotted in the complex plane shows semicircles. The system could be represented by an equivalent circuit of a bulk resistance in series with a parallel surface resistance-capacitance combination. The Cole-Cole diagrams have been used to determine the molecular relaxation time τ. The temperature dependence of τ is expressed by a thermally activated process. Analysis of the AC conductivity reveals semiconducting features based predominantly on a hopping mechanism.

Heterojunction cells of n-CdS0.5Se0.5/p-InP, fabricated by vacuum deposition of CdS0.5Se0.5 thin films into InP single crystals, show a conversion efficiency as high as 5% and an open circuit voltage of 0.78 V under illumination by light with a power density of 50 mW m−2 The CdS0.5Se0.5 films, nominally 400 nm thick, have resistivities of the order of 10−1 Ω cm, so that the film makes a good electrical contact between the junction and the front aluminium electrode. Measurements of J–V and C–V characteristics also have been evaluated to identify the mechanisms of barrier formation and current flow. At low voltages, the current in the forward direction varies exponentially with the voltage. At higher voltages, two distinct regions of ohmic and space-charge-limited conduction under forward bias are observed. The linearity of the C−2- V dependence is associated with a homogenous distribution of the impurities inside the space-charge region. Under a reverse bias, the conduction process at low voltage is determined by Schottky emission over a potential barrier of approximate height 0.88 eV and thickness 98 nm. At higher voltage levels, the Poole-Frenkel effect is observed.

A detailed study of current as a function of voltage at different temperatures, coupled with that of the dependence of current on sample thickness at a given voltage and temperature has been made in the C-direction of beta-cobalt phthalocyanine (beta-CoPc) single crystals using gold electrodes.Results show that at low voltages the conduction process is ohmic, while at high voltages space-charge-limited conduction is present. Traps with a density of 5.2 x 10(25) m(-3) located at 0.34 eV above the valence band edge have been observed. The voltage at which the transition from ohmic to space-charge-limited behaviour takes place has been found to be independent of the temperature. The results are interpreted in terms of the extrinsic nature; of ohmic conduction in beta-CoPc single crystals, The thickness dependence in the square-law region has been found to confirm the L(-3) law.

For monoporosa rapid fired tiles, eight fritted glaze formulae were designed to have soda feldspar in place of potash. Various ratios of frit/Kaolin and ZnO/ZrSiO4 were also tried. The properties of surface and interface of glazes were characterized through measuring their diffuse reflectance and pore development by scanning electron microscopy. Results were interpreted in terms of crystallite size and strain calculated from Xray line broadening. The cation coordination assessed by infrared analysis along with composition enlightened the glaze network structure. Detailed structural analyses aimed for future environmental studies. It was found that the reduced bubble formation in frits and hence elimination of pinholes and surface toughness in the glaze were related to high acidic glaze. The variation of ZnO and/or ZrSiO4 affected reflection and chromaticity as well as the size and shape of the pores developed in the interface. Results of stresses produced in the opacifier grains related to thermal expansion data of the glaze.

The electrical properties of In/β-CuPc-PVAc/Au (where CuPc is copper phthalocyanine and PVAc is polyvinyl-acetate) devices in the dark and under illumination have been studied. The temperature dependence of the photocurrent was attributed to a high trap density. Electron traps located at 0.25 eV below the conduction band have been observed. Schottky barrier parameters of the cell in the dark and under different monochromatic light intensities have been determined by a low frequency differential capacitance method. Light intensity increased significantly the space change density, which is a major concern as a possible limiting factor for the performance of organic solar cells.