Jacques Vedel

One step electrodeposition of CuInSe2: Improved structural, electronic, and photovoltaic properties by annealing under high selenium pressure

Films of Cu–In–Se alloys can be electrodeposited in a wide range of controlled composition. Annealing treatments under Se pressure transform these precursor films in large grain CuInSe2 films with improved electronic properties. These modifications are shown to depend on the Se pressure imposed during the treatment allowing a certain tailoring of the electronic properties of the films. The properties of electrodeposited/selenized films are presented as obtained from luminescence measurements, Hall effect, and photoelectrochemical characterization. An efficiency of 6.5% (total area, without antireflecting coating) is reported for the best CuInSe2/CdS/ZnO solar cell. An analysis of the device is also presented where limitations by interface recombination are shown to be the dominant loss mechanism.

Formation of copper indium diselenide by electrodeposition

The electrodeposition of copper indium diselenide has been studied in the presence of an excess of In(III) ions by voltammetric methods, X-ray diffraction analysis and chemical analysis of the deposits. It is shown that the presence of In(III) in the solution favours the reduction of Se(IV) to Se(II-) via the formation of CuInSe2. Two indium codeposition processes are observed. The first involves the formation of CuInSe2 + Cu2Se or CuInSe2 + In2Se3, depending on the ratio α of the Se(IV) flux to the CU(II) flux. It corresponds to an easier reduction of CuSe into Cu2Se and Se(II-). The second codeposition process results in a mixture of Cu + CuInSe2. It corresponds to an easier reduction of Cu2Se into Cu and Se(II-). The phases obtained under various conditions of potential and flux ratio are given.

Cathodic Deposition of Copper Selenide Films on Tin Oxide in Sulfate Solutions

The reactions accompanying the electrodeposition of binary copper selenium compounds from cupric sulfate and selenious acid solutions were studied by voltammetry. The deposits were chemically analyzed and the formed phases were identified by X-ray diffractometry. The deposit composition is determined by the fluxes of the Cu(II) and Se(IV) species arriving at the electrode in a relatively narrow potential range, from [minus]0.5 to [minus]0.8 V vs. MSE. For the more negative values of potential, only Cu[sub 2]Se is obtained as a solid but nonadherent compound. If there is a selenium excess, it is reduced to soluble selenide species. A model gives the distribution of the formed products as a function of the solution concentration and applied potential.

Investigation of the influence of the electrodeposition potential on the optical, photoelectrochemical and structural properties of as-deposited CdTe

Abstract The electrodeposition of cadmium telluride on cadmium sulphide deposited from a chemical bath is investigated with the aim of improving the structural and optical properties of the CdTe layers for solar cell applications. The CdTe layers are characterized by X-ray diffraction spectroscopy, optical transmission measurements and photoelectrochemical measurements. The influence of the electrodeposition potential on the conductivity type of the deposited CdTe is demonstrated. Spectral response measurements are used as an analytical method to study the optoelectronic properties of CdTe. Thickness-dependent spectral responses reflect a change of doping type for electrodeposition potentials more positive than +5 mV vs. the deposition potential of elemental cadmium. A front- and back-side illumination technique is used to determine the position of the active junction which varies between a n-CdS/p-CdTe and a n-CdTe|electrolyte junction. The width of the space charge layers and the doping concentrations are determined by using the Gartner equation for fitting the quantum efficiency vs. absorption coefficient plots.

Electrodeposition of indium selenide In2Se3

Indium selenide has been prepared by electrodeposition from indium sulphate and selenious acid solutions at 22 and 82°C. The deposits were analysed chemically and the films were characterised by anodic stripping, X-ray diffractometry and optical measurements. The reactions occurring during the process were studied. The formation of In2Se3 occurs via a reduction of Se(IV) into Se(-II), which then reacts with the In3+ ions to give In2Se3. Deposits prepared at 82°C have a better crystallinity than those obtained at 22°C. Optical characterisation of the electrodeposited In2Se3 gives a band gap energy of 1.58 eV. Voltammograms under illumination with the deposits as electrode material show a strong anodic photocurrent characteristic of an n-type semiconductor. Annealing at 390°C under an argon atmosphere increases the photocurrent.

Electrodeposition and Characterization of CulnSe2 Thin Films

Copper indium diselenide (CuInSe{sub 2}) presents a bandgap energy 0.95 < E{sub g} < 1.04 eV and a light absorption coefficient very well suited to the photovoltaic conversion of solar energy. Investigations have been done to prepare this material by electrodeposition in order to find a process that decreases the total cost of the devices. The codeposition process of the Cu-In-Se system has been studied. Electrodeposited films were prepared and analyzed for their chemical composition before and after annealing treatment. The whole composition of the films depends on the diffusion flux ratios of the species arriving at the surface of the electrode. With an excess of In(III) in the solution, the ratio of the Se(IV) and the Cu(II) fluxes is the key parameter setting the composition. Lower concentrations of In(III) involve the deposition of elemental selenium. In this case, the electrodeposition process is limited by the diffusion of the three species. An estimation of the diffusion fluxes is possible in order to predict the chemical composition of the films.

Epitaxial electrodeposition of CdTe films on InP from aqueous solutions: Role of a chemically deposited CdS intermediate layer

Epitaxial (111) CdTe films have been grown on (1 1 1) InP single crystals by one step electrodeposition in aqueous acidic solution, at a temperature of 85 °C, and a growth rate of about 0.7 μm h−1. Reflexion high‐energy electron diffraction and five‐circle x‐ray diffraction techniques have been used to characterize the interface structure and epitaxial quality. The epitaxy of CdTe (fcc a=6.49 A) takes place with a direct continuation of the InP lattice (fcc a=5.87 A), with no rotation of the respective crystallographic directions. The epitaxy is markedly improved when the InP substrate is covered with a thin film (20–30 nm) of epitaxial CdS grown by chemical bath deposition which acts as an interfacial buffer layer.

Electrodeposition of copper-selenium binaries in a citric acid medium

The electrodeposition of copper selenides from Cu(II) and Se(IV) solutions in citric acid was studied using voltammetry, chemical analysis and X-ray diffraction analysis. It is shown that at potentials less negative than an edge value, the composition of the deposit is determined by the diffusion fluxes of the solutes. According to various solution compositions, copper selenides (Cu2Se, Cu3Se2 and CuSe and their mixtures) are obtained. The edge potential corresponds to the reduction of the “higher” copper selenides (Cu3Se2 and CuSe) in Cu2Se. At more negative potentials, the copper(II) solute is reduced as Cu2Se and the excess of selenium(IV) as H2Se. In that case, the cuprous selenide does not adhere to the electrode.

Cathodic Codeposition of Cadmium Telluride on Conducting Glass

Films of cadmium telluride up to 5 μm thick were electrodeposited on glass plates covered with a conductive tin oxide layer sensitized by forming a thin layer of tin through cathodic prereduction. Castaings probe analysis indicates that the stoichiometric ratio Cd/Te is close to unity in a narrow potential deposition range

Photoelectrochemical study of p-type copper indium diselenide thin films for photovoltaic applications

Abstract A photoelectrochemical study of the behaviour of p-type thin films of CuInSe2 (CIS) in acqueous acidic solutions is presented showing that the liquid junction can be efficiently used for the characterization of as-grown layers. Standard films have doping levels in the range of 1016 cm−3 and their spectral responses present high quantum efficiencies (∼ 0.9). The films have a poor photoresponse in electrolyte without added redox species, which has been attributed to slow interfacial kinetics for the reduction of protons. The deposition on the surface of metal islands that catalyze the hydrogen evolution (Pd, Pt) greatly enhances the photoresponse allowing the transfer towards the solution of the internal photocurrent via the hydrogen evolution. With the addition of Eu3+ ions in solution, the transfer of photocurrent is achieved on bare surfaces allowing the complete characterization of the layer without surface treatment. Changes of the band edge position (i.e. barrier height changes) with the illumination were observed. They are associated with losses of about 0.5 V on the predicted open circuit voltage. The similitude with the behaviour of solid state cells is underlined.