Growth of Cu2S/CdS nano-layered photovoltaic junctions for solar cell applications

Layered Cu₂S/CdS photovoltaic p-n junctions were fabricated via a simple and reproducible route. CdS inner layer was grown on ITO substrate using chemical bath deposition process for different times. The utilized bath consisted of cadmium sulfate and thiourea with concentrations of 0.05 M and 0.07 M, respectively. CdS layer grown for 600 min was uniform with a thickness of about 500 nm. Moreover, band gap energy of the CdS inner layers was measured as 2.40-2.44 eV depending on the thickness of the layer. Cu₂S outer layer was formed over the CdS via ion exchange chemical route, in a bath consisting of copper chloride aqueous solution. EDS, XRD, and XPS were utilized to characterize the formation of cadmium sulfide, and copper sulfide phases during the fabrication steps of the p-n junctions. Nano-layered cell, each layer 200-250 nm in thickness was fabricated with an apparent band gap of 2.22 eV. SEM imaging of both inner and the outer layers confirmed the uniformity and homogeneity of the CdS and the Cu₂S layers.     

Effect of CdS modification on photoelectric properties of TiO2/PbS quantum dots bulk heterojunction

TiO₂/PbS(CdS) quantum dots (QDs) bulk heterojunction has been fabricated by successive ionic layer adsorption and reaction method via alternate deposition of PbS and CdS QDs. In comparison with TiO₂/PbS heterojunction, the incident photon to current conversion efficiency was increased almost 50% in the visible region. Meantime, the short-circuit current and open-circuit voltage were enhanced 200% and 35% respectively. The influence mechanism of CdS is related to reduction of trap state density at TiO₂/PbS interface and PbS QDs surface by the discussion of the dark current density–voltage curves, the transient photocurrent response curves and the electrochemical impedance spectra spectroscopy (EIS).     

The ionic Seebeck effect and heat of cation transfer in Cu2−δSe superionic conductors

The ionic Seebeck coefficients of Cu_2?δSe superionic conductors are measured in the temperature range 340–380°C. The data obtained are used to determine the heat of transfer Q _i of copper ions as a function of the degree of nonstoichiometry and the temperature. The heat of transfer of copper cations increases from 0.19 to 0.22 eV as the degree of nonstoichiometry δ increases from 0.015 to 0.050. It is noted that the heat of transfer Q _i tends to increase with an increase in the temperature. Assumptions regarding the specific features of the cation diffusion in the Cu_2?δSe superionic conductors are made from the observed closeness of the heat of transfer and the activation energy for ionic conduction.     

Positron annihilation study of helium clustering in alpha irradiated copper

Abstract

Helium clustering in alpha irradiated copper has been investigated by positron annihilation spectroscopy. Pure copper samples have been homogeneously helium implanted using a cyclotron, yielding helium concentrations of 100 appm and 400 appm. Post-implantation positron lifetime and Doppler broadened annihilation lineshape measurements have been carried out on these Cu samples as a function of isochronal annealing temperature. An annealing stage observed in the isochronal annealing curve viz., a marked reduction in the resolved lifetime τ₂ and an increase of its intensity I ₂, is explained as due to the formation of helium bubble embryos. At higher annealing temperatures, τ₂ corresponding to helium bubbles increases and saturates while its intensity I ₂ decreases, indicating an increase in the size of the bubble with a concomitant decrease in the bubble concentration. This stage is interpreted to be the bubble growth stage. From an analysis of positron lifetime parameters in the growth stage, helium stom density, bubble size and bubble concentration have been deduced at various annealing temperatures. The bubble characteristics are found to be affected by the helium dose. The present results on direct helium implanted Cu are compared with those of our earlier study on n-irradiated Cu-B, where helium was introduced using ¹⁰B(n, α)⁷ Li reaction.     

Nondestructive interface construction for CdS-buffered ZnO nanorod/Cu<Subscript>2</Subscript>O composite structure solar cells

In this work, ZnO nanorod/Cu₂O composite nanostructure solar cells were prepared using hydrothermal growth and electrodeposition. The CdS layer was added between ZnO and Cu₂O to suppress carrier reverse recombination. Nondestructive interface deposition methods were employed to prepare CdS and Cu₂O functional layers. The CdS layers were unconventionally deposited in non-alkaline solution, which can inhibit etching on the ZnO surface, and Cu₂O layers were electrodeposited in ZnO-buffered alkaline solution which can also inhibit etching on the ZnO surface. Finally, the performance of solar cells was improved by adding a highly resistive CdS intermediate layer between ZnO and Cu₂O layers. This work demonstrated the nondestructive interface approach of chemical solution deposition of functional layers on ZnO and possibilities for further improvements to the performance of Cu₂O-based nanostructure solar cells with the addition of an intermediated layer.     

Submicronic particles synthesis by a supercritical way

Abstract

The chemical transformation of metallic precursors in a supercritical fluid is a new route for obtaining nanometric homogeneous powders. In this paper we present a technique to produce metal, oxide or nitride submicronic particles, with a spherical morphology and mean diameters from a few microns to a few tens of nanometers. Metallic copper, oxides (Cu₂O, Fe₃O₄, Ga₂O₃) and nitrides (Cu₃N, Fe⁴N) have been prepared. This process consists in solubilizatiw and subsequent thermal decomposition of acetylacetonates of metals in a supercritical fluid, either a mixture of CO₂/C₂H₅OH or NH₃.     

EPR and Magnetic Susceptibility of Na2O–CuO–P2O5 Glasses

Abstract

(50?x/2)Na₂O–xCuO–(50?x/2)P₂O₅ glasses (x=1, 5, 15, or 30 mol%) have been prepared and characterized by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. The shape of the Cu²⁺ EPR spectrum depends on the Cu content, and the corresponding computer simulations suggest that the Cu²⁺ ions occupy two different sites in these glasses: one of them is preponderant at low Cu content and the other is preponderant at high content, in which the Cu²⁺–Cu²⁺ interactions are more important. From EPR parameters, it was found that for the site at low content, the covalency of copper ion bonding with the surrounding ligands is appreciable. The magnetic susceptibility data appear to follow the Curie–Weiss law (χ=C/(T?θ_p)) with negative paramagnetic Curie temperature θ_p indicating antiferromagnetic interactions between Cu²⁺ ions that are more significant in the samples with high Cu content, in agreement with EPR results.     

Fabrication of cuprous and cupric oxide thin films by heat treatment

Cuprous oxide (Cu₂O) and cupric oxide (CuO) thin films were prepared by thermal oxidation of copper films coated on indium tin oxide (ITO) glass and non-alkaline glass substrates. The formation of Cu₂O and CuO was controlled by varying oxidation conditions such as, oxygen partial pressure, heat treatment temperature, and oxidation time. The microstructure, crystal direction, and optical properties of copper oxide films were measured with X-ray diffraction, atomic force microscopy, and optical spectroscopy. The results indicated that the phase-pure Cu₂O and CuO films were produced in the oxidation process. Optical transmittance and reflectance spectra of Cu₂O and CuO clearly exhibited distinct characteristics related to their phases. The electrical properties indicated that these films formed ohmic contacts with Cu and ITO electrode materials. Multilayers of Cu₂O/CuO were fabricated by choosing the oxidation sequence. The experimental results in this paper suggest that the thermal oxidation method can be employed to fabricate device quality Cu₂O and CuO films that are up to 200–300 nm thick.     

HREM studies of structural defects in high-Tc superconductors of “123” type

Abstract

High resolution transmission electron microscopy (HREM) has been used to reveal directly the structure of the metal framework and its defects in YBa₂Cu₃O_7–δ and HoBa₂Cu₃O_7–δ high-Tc superconductors. Metal atoms are seen as dark spots with different contrast depending on the atomic scattering factors. The spots arising from the oxygen columns in the Cu(1) planes are distinguished as brighter regions. Twin boundaries were observed as well as different kinds of extrinsic planar faults studied through comparison between the experimental HREM images and the corresponding structural models which were constructed.     

Pressure dependence of high-Tc superconductors

Abstract

We recently developed a method to derive the charge carrier concentration 6 (holes per planar copper atom) under pressure from the measured T_c and H_c2. The different behaviour of YBa₂Cu₄O₈, CaLaBaCu₃)₇ and other compounds can be understood from the difference in ?δ/?p using a model where T_c is quadratically dependent upon δ and where δ is linearly dependent upon pressure, as observed experimentally.     

Hole doping by Li substitution and antiferromagnetism in YBa Cu O studied by neutron powder diffraction measurements

The magnetic structure of tetragonal insulating YBa₂Cu_3-xLi_xO_y has been studied as a function of x and y. The Néel temperature and the mean ordered magnetic moment on the Cu2 sites were determined by neutron powder diffraction measurements. The decrease of these two parameters as compared to YBa₂Cu₃O₆ is much stronger for lithium than for zinc substitution. The difference is quantitatively explained by the presence of holes created in the CuO₂ planes. These holes arise from the substitution of plane Cu²⁺ by Li⁺. We suggest an explanation why such holes are not seen for the same substitution of plane Cu²⁺ by Li⁺ in orthorhombic superconducting YBa₂Cu_3-xLi_xO _{7 - δ} . Received 31 October 2001 and Received in final form 6 March 2002 Published online 25 June 2002     

Silver-tracer diffusion in Cu2O

The diffusion of¹¹⁰Ag in Cu₂O has been measured by a serial-sectioning technique as a function of temperature (700–1132°C) and oxygen partial pressure (6 × 10^?6 ?8 × 10^?2 atm). The data are fit to the defect model for Cu₂O developed by the authors in the preceding paper. Silver ions have a larger impurity-vacancy binding free energy and/or a larger jump frequency for the singly charged cation vacancies relative to that for the neutral cation vacancies. The activation enthalpies for the diffusion of copper and silver ions in Cu₂O are nearly equal, but the absolute value of D¹_Ag is about three times larger than D¹_Cu even though the silver ion is 31% larger than the copper ion.     

Uracil-Appended Fluorescent Sensor for Cu2+ and Hg2+ Ions: Real-Life Utilities Including Recognition of Vitamin B2 (Riboflavin) in Milk Products and Invisible Ink Applications

A simple uracil-appended fluorescent sensor (1) has been developed by one pot reaction and characterized by using common spectroscopic methods such as UV-vis, Fluorescence, HRMS and FT-IR analyses. Upon addition of various metal ions to the CH₃CN solution of sensor 1, the fluorescence was quenched in the presence of Cu²⁺ / Hg²⁺ ions. The limit of detection for Cu²⁺ and Hg²⁺ was calculated to be 3.31 and 0.316 µM, respectively. Further, the sensor was applied for real-life applications in the determination of Vitamin B₂ (riboflavin) and its presence in milk products. With the incorporation of different sources of vitamin-B to acetonitrile solution of it, there was discernible fluorescence enhancement only in the presence of vitamin B₂. Also, it has been successfully applied for the detection of Vitamin B₂ (riboflavin) in milk and curd. Moreover, based on the fluorescent color changes, the sensor was utilized for invisible ink applications.

     

Preparation of Cu 2 O nanoparticles dispersed in NH 2 -terminated polyethyleneoxide matrix

Small Copper (I) oxide, Cu₂O, nanoparticles dispersed in diamine-terminated polyethyleneoxide (PEO-NH₂) matrix have been successfully prepared by vacuum evaporation of copper onto the molten PEO-NH₂. The obtained composite were characterized by TEM, electron diffraction, TG-DTA and FT-IR spectroscopy. The stable composite, in which the Cu₂O nanoparticles are stabilized through interaction between NH₂ chain end groups of PEO molecules and Cu₂O nanoparticles was obtained when the samples were heat-treated at 110 ^° C. The mean size of the Cu₂O nanoparticles increased from 2.5 to 3.5 nm in diameter upon increasing the amount of initial Cu deposition. The obtained composite material having a waxy texture was soluble in many solvents without aggregation and can be handled as a simple chemical compound for starting material in various applications. Received 29 November 2000     

Shift of the Fermi level during cointercalation of copper and iron into TiSe<Subscript>2</Subscript>

The influence of copper intercalation into the TiSe₂ compound on the Fermi energy has been investigated using two independent methods. The first method is based on the analysis of the amplitude of the deformation (induced by impurity intercalation and providing the formation of polarons) as a function of the binding energy of the band of polaron states. For this purpose, the Fe _x Cu _y TiSe₂ system has been synthesized for the first time by cointercalation of copper and iron into the TiSe₂ lattice and studied. The second method consists in measuring the electromotive force of an open-circuit electrochemical cell with respect to a metal reference electrode. Both methods lead to consistent results in the range of moderate copper contents. However, considerable discrepancies have been observed in the copper concentration range that corresponds to the beginning of filling of Cu/Ti hybrid states. These discrepancies are explained by the softening of the lattice due to an increase in the density of states at the Fermi level.     

High-pressure properties of high-TC superconductor samples produced by hot isostatic pressing

Abstract

The electrical resistance of dense YBa₂Cu₃O_x and YBa₂Cu₄O_y produced by hot isostatic pressing has been measured vs. T and p. At 295 K we find d (ln R)/dp ? -0.12 and -0.09 GPa^?1, respectively, with no systematic dependence on initial density. For 1-2-4, dT_C/dp ? 5.1 K/GPa, which is ten times that of 1-2-3.     

Ab initio study of heterojunction discontinuities in the ZnO/Cu2O system

Solar cells based on transparent conductive oxides such as ZnO/Cu₂O constitute a very advanced way to build high-performance cells. In this work, we are interested in the characterization of the interface through nanoscale modeling based on ab initio approaches (density functional theory, local density approximation, and pseudopotential). This work aims to build a supercell containing a heterojunction ZnO/Cu₂O and study the structural properties and the discontinuity of the valence band (band offset) from a semiconducting to another phase. We build a zinc oxide in the wurtzite structure along [0001] on which we place the copper oxide in the hexagonal (CdI₂-type) structure. We choose the method of Van de Walle and Martin to calculate the energy offset. This approach fits well the density functional theory. Our calculation of the band offset gives a value that corresponds to other experimental and theoretical values.     

Dufour effect in superionic copper selenide

The Dufour effect has been observed in the superionic conductor copper selenide, Cu_2−x Se. This effect is the opposite of the Soret thermal diffusion effect which was previously only observed in gaseous and liquid systems. Fiz. Tverd. Tela (St. Petersburg) 40, 242–244 (February 1998)     

High pressure raman study of Y-124

In this work, a micro-Raman study under high hydrostatic pressure (up to ～5.5 GPa) has been carried on YBa₂Cu₄O₈ and Y(Ba, Sr)₂Cu₄O₈ single crystals at room temperature. In both samples, seven strong modes, of A_g symmetry, and one weak, of B_3g symmetry, have been observed and examined in connection with previously published results concerning YBa₂Cu₄O₈. With the Sr substitution for Ba, the ambient pressure measurements show an upward shift in energy for all modes, except those that involve vibrations of the plane and apex oxygen atoms. With increasing hydrostatic pressure all phonons shift to higher energies. Anomalous nonlinear pressure behaviour has been observed for three phonons, which is correlated with the pressure dependence of T _c of these compounds.     

Optical characterization of thin thermal oxide films on copper by ellipsometry

A complete optical characterization in the visible region of thin copper oxide films has been performed by ellipsometry. Copper oxide films of various thicknesses were grown on thick copper films by low temperature thermal oxidation at 125 °C in air for different time intervals. The thickness and optical constants of the copper oxide films were determined in the visible region by ellipsometric measurements. It was found that a linear time law is valid for the oxide growth in air at 125 °C. The spectral behaviour of the optical constants and the value of the band gap in the oxide films determined by ellipsometry in this study are in agreement with the behaviour of those of Cu₂O, which have been obtained elsewhere through reflectance and transmittance methods. The band gap of copper oxide, determined from the spectral behaviour of the absorption coefficient was about 2 eV, which is the generally accepted value for Cu₂O. It was therefore concluded that the oxide composition of the surface film grown on copper is in the form of Cu₂O (cuprous oxide). It was also shown that the reflectance spectra of the copper oxide–copper structures exhibit behaviour expected from a single layer antireflection coating of Cu₂O on Cu. Received: 19 July 2001 / Accepted: 27 July 2001 / Published online: 17 October 2001