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.

Measurements of the temperature dependence of ohmic and space-charge-limited (SCL) currents on thin films of polycrystalline particles of cadmium telluride in Schottky-junction cells have been carried out in air ambient. These cells showed rectification where p-CdTe material was flanked between an ohmic contact (Au) and a blocking contact (Al). At low voltages, the dark current in the forward direction which corresponds to negative potential at the Al electrode varies exponentially with voltage. At higher voltages, two distinct regions of ohmic and SCL conduction limited by a discrete trapping level are determined. Traps with a density of 3.85×1022m−3 located at 0.58eV above the valence band edge have been observed. The thickness dependence in the square-law region has been found to confirm the d−3 law. Values of conversion efficiency as high as 11.3% and open-circuit voltage of 0.77V have been evaluated from the photo-measurements of J–V characteristic at input power density of 100mWcm−2. Space-charge concentrations and barrier heights have been estimated from the capacitance–voltage (C–V) measurements both in dark and under constant illumination. The linearity of the C−2–V dependence is associated with a homogenous distribution of the impurities inside the space-charge region.

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.

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 .

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.

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.

Current density-voltage characteristics were obtained from 2,6-diamino anthraquinone samples using ohmic aluminium electrodes. Results showed that at low voltage the conduction process was ohmic, while at high voltage space-charge-limited conduction controlled by a single dominant trap level was presented. Thickness dependence measurements proved that the trapping sites were located at a discrete energy level. The transition voltage, V(t), between ohmic and space-charge-limited conduction was approximately proportional to the square of the sample thickness and was found to be temperature independent. The temperature dependence of ohmic and space-charge-limited current densities have been investigated. The results were interpreted in terms of extrinsic nature of ohmic conduction. Traps with density almost-equal-to 2 x 10(24) m-3 located at 0.50 +/- 0.03 eV below the conduction band edge have been observed.

The kinetics of electron transfer reaction across a layer of tin oxide formed on tin electrodes were measured in borate buffer pH = 8. The effect of concentration of the redox system, Fe(CN) 3− 6 /Fe(CN) 4− 6 , on the rate of the process and also the effect of oxide thickness were measured by cathodic and anodic polarization curves. A reaction order of 0.7 with respect to the redox system was found. An exponential dependence of the exchange c.d, i 0 , on film thickness was interpreted on the basis of direct tunnelling through the oxide. Thick films formed at potentials within the O 2 -evolution range showed increase of i 0 as function of film thickness.

AbstractWährend das erste von jeweils 2 Halbstufenpotentialen bei der polarographischen Reduktion der Titelverbindungen (I) der Spaltung der Diazogruppe unter Bildung von (II) und den entsprechen‐ 40 den Anilinen zugeordnet wird (‐0. 1 8 bis +0.l4 V), gehört das 2.Halbstu‐fenpotential (‐0.78 bis +O.53 V) zur Reduktion von (II) zum Produkt (III).

The polarographic behaviour of a series of arylazothiohydantoin derivatives has been investigated at a dropping mercury electrode. Two waves were displayed. The first and predominant one is due to the reductive splitting of the azo-linkage by a 4e irreversible process. The second is assumed to be for the reduction of the CONHCO group in the resulting molecule. A mechanism for the electrode process covering a wide range of pH is proposed, discussed, and clarified via model compounds, identification of the resulting products of electrolysis, pKa determinations, and the interpretation of σ–E½ plots.

Die Korrosion von Eisen in 1N H 2 SO 4 wurde mit Hilfe von elektrochemischen Polarisationsmessungen untersucht. Der Einfluβ des Zusatzes von einigen anorganischen Salzen wurde ermittelt. K 2 Cr 2 O 7 steigerte die Korrosionsgeschwindigkeit, NH 4 CNS und KI wirkten als Inhibitoren. Thioharnstoff wirkte in Konzentrationsbereichen von 1–3×10 −3 Mol/l gleichfalls als Inhibitor. Aus den kathodischen Polarisationskurven wurde die Bedeckungsdichte der Oberfläche mit den Inhibitoren berechnet, und es wurden ferner Korrosionsmessungen bei Zusatz von Mischungen aus Thioharnstoff und anorganischen Salzen durchgeführt. Dabei wurde festgestellt, daβ K 2 Cr 2 O 7 , NH 4 CNS und KI die Inhibitionswirkung des Thioharnstoffs beeinflussen.