CuS Films Research Articles

Preparation of multinary thin films by mass spectrometer control

Chalcopyrite films of Cu(Ga, In)Se 2 are well known as highly efficient absorbers for thin film solar cells. In order to obtain multinary semiconducting films with optimized properties deposition conditions ( i.e. metal fluxes) have to be controlled precisely. This is especially important in the manufacture of large area devices. Films have been prepared by simultaneous thermal evaporation of the single elements in a high vacuum system. The fluxes of the metals are controlled by a quadrupole mass spectrometer with a cross-beam ion source. Reproducibility and precision have been improved in comparison with temperature-controlled crucibles. A special concentric source that can independently control two (or three) different species has been designed. Its application has demonstrated the possibility of producing large area films with high homogeneity in composition. The first monolithically integrated modules have been prepared with conversion efficiencies up to 6.7%.

Photovoltaic Properties of Cuprous Chalcogenide-Silicon Junctions

Cu2Te thin films were deposited on glass and n-type Si substrates by vacuum evaporation, and electrical and photovoltaic properties were investigated. Cu2Te thin films show p-type and low resistive conduction, and have carrier density of 1021 cm-3 and Hall mobility of 3–10 cm2/V·sec. Cu2Te–Si junctions have low photovoltaic properties, therefore Cu2Se film was deposited on Cu2Te layer making a structure of Cu2Se–Cu2Te–Si junctions. The maximum solar conversion efficiency of this structure was 9.2% under the sunlight of 83 mW/cm2.

Electroluminescence from Cu2S-ZnS: Mn, Cu, Cl Heterojunctions

Electroluminescence (EL) was observed in heterojunctions between Cu2S film and ZnS: Mn, Cu, Cl film prepared individually by two-step evaporation. In sandwich-type cells (Cu2S–ZnS: Mn, Cu, Cl–NESA), current-voltage, capacitance-voltage, brightness-voltage characteristics and oscillograms of the brightness waveform under excitation by full wave sinusoidal voltages were measured. The emitting portion in gap-type cells (Cu2S–ZnS: Mn, Cu, Cl–Cu2S) under dc excitation was observed by a microscope. From these results, EL from Cu2S–ZnS: Mn, Cu, Cl heterojunctions prepared by two-step evaporation seems to be just the same as EL from ZnS: Mn, Cu, Cl films prepared from the evaporant with excess Cu by one step evaporation.

Structure and electrical properties of thin films of copper selenide

Electron-diffraction and electron-microscope methods were used to investigate the structure of Cu2Se films of close to stoichiometric composition. It is shown that in polycrystalline and single-crystal films of thickness >400A at room temperature, the tetragonal modification is stable, which at temperatures above 400°K is transformed into the cubical modification. In thinner films d<400 A the cubical modification of copper selenide is stable at room temperature. A sharp peak is observed at 400°K on the temperature dependence of the resistance; this is connected with the phase transition. At room temperature, copper selenide is a degenerate p-type semiconductor with carrier concentration 5 · 1022–8 · 1020 cm−3, depending on the thickness of the film.

Development of superior colored finishes for copper and copper alloys

A multitude of attractive colors can be produced on copper and copper alloys by simply immersing the metal in selenious acid solution of controlled concentration and pH at room temperature. However, these colors, with certain exceptions which have been noted, are not stable in the atmosphere and must be protected by a layer of clear lacquer. The following overall reaction is proposed: 19Cu + 15 H 2SeO 3 + 5 H 2O = 10(CuSeO 3.2 H 2O) + 5 Cu 1·8Se. X-Ray diffraction and electron diffraction studies of the colored film indicated that it consists of Cu 1·8Se and CuSeO 3.2H 2O. However, the active coloring material is Cu 1·8Se. The thickness of the film was determined by an electrochemical method and found to vary between 100 Å and 700 Å. These values indicate that the colors are due to interference effects. It is particularly significant that comparable colors are provided by films of Cu 2Se, Cu 2S and Cu 2O. In the case of the selenide and oxide films, the film thickness is essentially the same for similar colors. Numerous compounds were studied as additives to the selenious acid solution, with a view to obtaining formulations yielding a wider range of uniform colors. As a result of this work, three formulations are recommended which yield specific brown colors which are essentially independent of immersion time, and which hold some promise for a durable statuary finish.

Effects of Deposition Time on the Chemical Bath-deposited CuS Thin Films

The chemical bath deposition technique was used to deposit thin films of coppersulphide onto indium tin oxide glass substrates. The bath composition included copperchloride which was the source of Cu2+ and sodium thiosulfate which supplied the S2- ions. Xraydiffraction and atomic force microscopy were used to investigate structural andmorphological characterization, respectively. The influence of deposition time was studiedto determine the optimum condition for deposition process. The deposited CuS films showedhexagonal structure. The number of peaks attributable to CuS increased as the depositiontime was increased to 16 hours based on XRD data. AFM images revealed that the chemicalbath-deposited films for 16 hours showed more homogeneous and uniform compared withother deposition times, and the highest absorbance value was obtained for the filmsdeposited at this period. The band gap energy decreased from 2.9 to 2.45 eV when thedeposition time was increased from 8 to 20 hours.Keywords: Chemical bath deposition, copper sulphide, thin films, solar cells.DOI: 10.3126/jncs.v25i0.3276Journal of Nepal Chemical Society Volume 25, 2010 pp 2-8