Molybdenum Coated Glass Substrates Research Articles

Structural, SEM and Nucleation Characterization of Electrochemically Synthesized CuInSe2 Thin Films

Near-stoichiometric CuInSe2 thin films were synthesized by one-step electrodeposition on molybdenum-coated glass substrates. Cyclic voltammetry measurements were firstly used to investigate the electrodeposition mechanisms. The electrochemical, structural, composition and nucleation properties of these films were investigated by cyclic voltammetry, scanning electron microscopy (SEM) and x-ray diffraction (XRD) using an energy dispersive x-ray spectrometer. Analysis of the nucleation mechanisms indicated that the electrodeposition of CuInSe2 from a single bath solution involved an instantaneous 3-D nucleation. An appropriate deposition-imposed potential range of −700 to −400 mV/SCE was determined, although the reduction peak of indium occurred around −960 mV/SCE. The most suitable deposition potential for film preparation was determined to be −500 mV/SCE. The XRD results showed that the films exhibit a polycrystalline tetragonal CuInSe2 phase with (112) orientation. The composition of the film deposited at −500 mV/SCE is very close to the stoichiometric ratio of 1:1:2 according to energy-dispersive x-ray spectroscopy measurements. We discuss the results obtained for the SEM and structural properties of the latter films, which were subjected to a post-annealing process under vacuum at temperatures of 300, 400 and 500°C for 30 min.

Thickness-dependent structural parameters of kesterite Cu2ZnSnSe4 thin films for solar cell absorbers

The influence of thickness on the structural parameters, off-stoichiometry and cation disorder in kesterite Cu2ZnSnSe4 films grown by flash deposition for solar cell absorbers is investigated employing X-ray diffraction, energy-dispersive X-ray and Raman spectroscopies. It is shown that the lattice parameters of Cu2ZnSnSe4 changed depending on film thickness: the 100 nm film turned out to be weakly stretched on the molybdenum-coated glass substrates, while, in the thicker films, the compressive deformation is defined. The causes of the changes in film structure are outlined. Raman spectra revealed secondary phases like Cu2SnSe3 detecting reduction of its fraction with an increment in thickness; also, the SnZn antisite defect fraction decreases. Simultaneously, the share of disordered kesterite phase associated with CuZn antisite defects rises with thickness. The obtained results can be useful for optimization of technological growth process.

Local growth of CuInSe2 micro solar cells for concentrator application

A procedure to fabricate CuInSe2 (CISe) micro-absorbers and solar cells for concentrator applications is presented. The micro-absorbers are developed from indium precursor islands, which are deposited on a molybdenum coated glass substrate (back contact), followed by deposition of copper on top and subsequent selenization as well as selective etching of copper selenides. In order to compare the properties of the locally grown absorbers to those of conventional large area CISe films, we systematically examine the compositional and morphological homogeneity of the micro absorbers and carry out photoluminescence measurements. Preliminary devices for micro-concentrator solar cell applications are fabricated by optimizing the copper to indium ratio and the size of the indium precursor islands. The resulting micro solar cells provide a characteristic I–V curve under standard illumination conditions (1 sun).

Fabrication of Cu3BiS3 Photocathode for Photoelectrochemical Hydrogen Evolution

Hydrogen production from water using abundant solar light is now an important research subject from viewpoints of usage of renewable energy and environmental issues. Photoelectrochemical (PEC) water splitting utilizing semiconductor electrodes has been studied extensively as a potential means of converting solar energy into chemical energy in the form of H2. Chalcogenide compounds have emerged as a leading class of thin films for photocathodes due to their suitable band gap for solar energy absorption, high photo-absorption coefficients, and usability in the polycrystalline state. Although Cu-chalcogenide photocathodes such as CuInS2,CuGaSe2, CuGa3Se5,(Ag,Cu)GaSe2, and Cu(In,Ga)Se2, show excellent solar-to-hydrogen conversion efficiency, there are many difficulties in largescale production from the viewpoints of low throughput and material utilization because of the limited availably of elements (i.e., In, Ga and Se). It is therefore evident that more research is required to search for alternative inexpensive and earth-abundant materials. Cu3BiS3 is one of the promising chalcogenide compounds for a photovoltaic device due to its ability to absorb visible light (Eg ≈ 1.4–1.7 eV), a high absorption coefficient (>105 cm-1) compared to that of CuInSe2 and Cu2ZnSnS4, and p-type conductivity with a carrier concentration of ~ 2×1016 cm-3 . Moreover, it is made of cheap, non-toxic, earth-abundant elements and can be easily produced on a large scale. We fabricated a Cu3BiS3 thin film by a simple electrodeposition technique on a molybdenum-coated glass substrate to utilize it as a photocathode for PEC hydrogen evolution. The Cu3BiS3 film was composed of dense crystallites with thicknesses of ca. 0.65 μm, and the optical bandgap was estimated to be ca. 1.6 eV. Photoelectrochemical characterization revealed that the Cu3BiS3 film was a p-type semiconductor with a flat band potential of ca. +0.1 V (vs Ag/AgCl at pH 6), which is suitable for water reduction but cannot be used for water oxidation. Deposition of an In2S3 buffer layer, by which effective contact between p-type Cu3BiS3 and n-type In2S3 was formed, resulted in a significant increase in the photocurrent and a large shift of the photocurrent onset to the positive region. H2 evolution under AM 1.5G simulated solar light was demonstrated using the Pt-In2S3/Cu3BiS3 electrode combined with a Pt electrode under an applied bias (0 V vs. RHE).

Platinum and indium sulfide-modified Cu3BiS3photocathode for photoelectrochemical hydrogen evolution

Platinum-deposited In2S3/Cu3BiS3film as a photoelectrode was fabricated on a molybdenum-coated glass substrate for photoelectrochemical hydrogen evolution.

Growth and shape of indium islands on molybdenum at micro-roughened spots created by femtosecond laser pulses

Indium islands on molybdenum coated glass can be grown in ordered arrays by surface structuring using a femtosecond laser. The effect of varying the molybdenum coated glass substrate temperature and the indium deposition rate on island areal density, volume and geometry is investigated and evaluated in a physical vapor deposition (PVD) process. The joined impact of growth conditions and spacing of the femtosecond laser structured spots on the arrangement and morphology of indium islands is demonstrated. The results yield a deeper understanding of the island growth and its precise adjustment to industrial requirements, which is indispensable for a technological application of such structures at a high throughput, for instance as precursors for the preparation of Cu(In,Ga)Se2 micro concentrator solar cells.

Synthesis, annealing, characterization, and electronic properties of thin films of a quaternary semiconductor; copper zinc tin sulfide

ABSTRACTCopper zinc tin sulfide thin films were successfully prepared by spin coating on Molybdenum-coated glass substrates. The as-deposited thin films were annealed at 400°C, 450°C, and 500°C in an Argon atmosphere for 1 hr. X-ray diffraction studies revealed that the thin films present the kësterite phase. The band gap decreased with increasing annealing temperature. Schottky barrier-type structures were fabricated and showed a rectifying behavior. The estimated values of the barrier height, the built-in voltage, and the doping density were, respectively, ΦB = 0.71 eV, Na = 5 × 1018 cm−3, and Vbi = 0.33 V for annealed films.

Cu2ZnSnS4solar cells with a single spin-coated absorber layer prepared via a simple sol-gel route

Carbon-free Cu2ZnSnS4 (CZTS) thin films were prepared via a simple spin-coating process based on a sol–gel precursor of methoxyethanol solution with metal salts and thiourea, followed by post-sulfurization. The sol–gel precursor solution was deposited onto molybdenum-coated glass substrates. The sulfurization process was carried out using a conventional furnace at 525 °C for 60 min in a nitrogen atmosphere with sulfur powder. The structural, morphological and compositional properties of as-sulfurized thin films were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy and Auger electron spectroscopy. Only a single coating of the precursor solution was applied to obtain uniform Zn-rich and Cu-poor CZTS films thicker than 1 µm after post-annealing. The best solar cell fabricated with the as-prepared CZTS films of band gap energy ~1.37 eV showed a short-circuit current density of 10.15 mA/cm2, an open circuit voltage of 0.509 V, a fill factor of 33.72% and a conversion efficiency of 1.74%. Copyright © 2015 John Wiley & Sons, Ltd.

Quality CuInSe2 and Cu(In,Ga)Se2 thin films processed by single-step electrochemical deposition techniques

Ternary CuInSe2 and quaternary Cu(In,Ga)Se2 chalcopyrite semiconductor films with potential applications as solar absorbers were deposited by single-step electrochemical deposition (ECD) on molybdenum coated glass substrates. The films have been structurally characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy dispersive x-ray analysis (EDAX), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Chalcopyrite phase formation was confirmed already in as-deposited films. The crystal structure of the films was further improved by thermal treatment. Element interdiffusion at the chalcopyrite/Mo/glass interface has been prevented by retaining moderate temperatures of deposition (70 °C) and subsequent annealing (300 °C). The SEM/EDAX analysis revealed the presence of CuxSe secondary phases on the surface of ternary films and almost stoichiometric growth of quaternary deposited on top of ternary films. The XRD and Raman analysis confirmed the high quality assessment of the films being almost equal to that of chalcopyrite selenide layers grown by physical vapor deposition at high temperatures (550–750 °C). The surface sensitive XPS analysis confirmed the absence of other impurities in the ECD processed films except from oxygen and carbon adsorbents by sample exposure to atmospheric air.

On the properties of Cu2ZnSn(S,Se)4 thin films prepared by selenization of binary precursors using rapid thermal processing

Cu2ZnSn(S,Se)4 thin films were grown on molybdenum coated glass substrates by selenization of stacked precursor layers of zinc, tin disulfide and copper sulfide. Selenization was performed using a rapid thermal processor at maximum temperatures in the range of 400 °C to 550 °C and at heating rates of 1 °C /s and 2 °C /s. The compositional, morphological and structural characterization of the films was carried out using energy dispersive x-ray spectroscopy, scanning electron microscopy, x-ray diffraction and Raman spectroscopy. X-ray diffraction and Raman scattering analysis suggests the formation of Cu2ZnSn(S,Se)4 only at lower temperatures, whereas Cu2ZnSnSe4 was formed at higher temperatures regardless of the heating rate used. Compositional analysis revealed that the films were Zn-poor and Sn-rich. However, the samples approach a near stoichiometric composition due to the loss of tin at a selenization temperature and heating rate of 550 °C and 2 °C /s, respectively. Large grains with an average lateral dimension of 4.5 μm were observed for films prepared at these conditions which are very desirable for an absorber for solar cells.

Locally resolved investigation of wedged Cu(In,Ga)Se 2 films prepared by physical vapor deposition using hard X-ray photoelectron and X-ray fluorescence spectroscopy

We have investigated a specially grown Cu(In,Ga)Se2 (CIGSe) absorber, which was deposited by co-evaporation of Cu, In, Ga, and Se using a modified three stage process. Prior to the growth, the molybdenum-coated glass substrate was covered by a bent shroud made from tantalum (Ta), leading to a wedged absorber structure with a width of about 2 mm where the film thickness varies from 0 to 2 μm. In this region of interest the thickness dependency of morphology, concentration ratios and electronic properties was studied with secondary electron microscopy (SEM), X-ray fluorescence (XRF) and hard X-ray photoelectron spectroscopy (HAXPES), probing the CIGSe sample along the thickness gradient. The evidence of the thickness gradient itself was proven with SEM measurements in cross section geometry. By using XRF it was found that with decreasing film thickness the Cu concentration decreases significantly. This finding was also verified by HAXPES measurements. Furthermore, an enrichment of Ga towards the Mo back contact was found using the same technique. Besides these results the formation of a molybdenum selenide (MoSe) phase was observed on the fully covered part of the Mo coated substrate indicating a high mobility of Se on Mo under the given temperature conditions of the modified three stage deposition process.

Flash-lamp annealing of ZnO-layers on copper–indium–gallium–sulphide layers: A spectroscopic ellipsometry study

Polycrystalline copper–indium–(gallium)–sulphide (CI(G)Su) absorbers were analysed by spectroscopic ellipsometry (SE) with special emphasis on the optical band gap energy. Rough CI(G)Su absorber films grown by reactive magnetron sputtering were peeled off from molybdenum coated glass substrates. The smooth back side of CI(G)Su absorbers was suited for the SE analysis. Furthermore, these samples were covered with a thin zinc oxide (ZnO) layer and heat-treated with a commercial xenon flash lamp annealing system (FLA) as well as by thermal annealing in an argon atmosphere. The effect of zinc on CI(G)Su absorber films was studied by secondary ion mass spectrometry depth profiling as well as by SE analysis. The optical modelling of spectral Stokes parameters was performed by using a multilayer approach over a spectral range from 1.5 to 4.3eV. Spectral absorption coefficients were calculated in every process stage, i.e. (i) peeled samples, (ii) ZnO deposition, (iii) FLA treatment and (iv) etching of the ZnO. Special emphasis was given to the shift of the optical band gap due to the various treatments. While the SE analysis was quite sensitive to the change of optical band gaps due to a varying gallium content in the CI(G)Su absorber layers, a significant shift of the optical band gap due to increasing zinc content was not detectable.

Synthesized and Characterization of Cu<sub>2</sub>ZnSnS<sub>4</sub> (CZTS) Thin Films Deposited by Electrodeposition Method

Cu2ZnSnS4(CZTS) thin films was potentiostatically deposited on molybdenum coated glass substrates using the electrochemical deposition method As-deposited and annealed in furnace, The polycrystalline CZTS thin films with tetragonal crystal structure have been studied from structural analysis results , XRD and Raman spectroscopy results show these thin films exhibit a strong preferential orientation along the (112), The energy gap of Cu2ZnSnS4 was estimated to be 1.8 eV via ultravioletvisible (UVvis) absorption spectrum of Cu2ZnSnS4 which suggests that CZTS films Can be useful as an absorber layer in thin film solar cells.

Homogeneous electrochemical deposition of in on a Cu-covered Mo substrate for fabrication of efficient solar cells with a CuInS2 photoabsorber

Electrochemical deposition of indium (In) on a copper-covered molybdenum-coated glass substrate from several acidic InCl3 solutions was studied for fabrication of CuInS2-based solar cells. When In was deposited using a simple acidic InCl3 solution at −0.80V (vs. Ag/AgCl), island-shaped growth was observed, whereas a homogeneous In film was obtained from InCl3 solution containing citric acid and sodium citrate at −0.98V (vs. Ag/AgCl). Electrochemical and structural analyses revealed that the citric acid additive had a function for smoothing the surface of the In deposit. The mixing with sodium citrate induced appreciable inhibition of H2 evolution during the In deposition, leading to high current efficiency of >90%. The CuInS2 film derived from the homogeneous In had a uniform thickness with a smooth surface, while the CuInS2 film obtained from the island-shaped In deposit showed a large variation in thickness with recessed areas. The CuInS2 film derived from the homogeneous In was showed better photoelectrochemical response than that of the film fabricated from the island-shaped In. As expected from these differences, the solar cell with an Al:ZnO/CdS/CuInS2/Mo structure derived from the homogeneous In film showed the best conversion efficiency of 7.8% with relatively high reproducibility.

Optical properties of high quality Cu2ZnSnSe4 thin films

Cu2ZnSnSe4 thin films, fabricated on bare or molybdenum coated glass substrates by magnetron sputtering and selenisation, were studied by a range of techniques. Photoluminescence spectra reveal an excitonic peak and two phonon replicas of a donor-acceptor pair (DAP) recombination. Its acceptor and donor ionisation energies are 27 and 7 meV, respectively. This demonstrates that high-quality Cu2ZnSnSe4 thin films can be fabricated. An experimental value for the longitudinal optical phonon energy of 28 meV was estimated. The band gap energy of 1.01 eV at room temperature was determined using optical absorption spectra.

Electrodeposited Cu-In-Ga-Se Precursor Layers

Cu-In-Se (CIS) and Cu-In-Ga-Se (CIGS) thin films have been prepared by the electrodeposition technique on molybdenum-coated glass substrates. In this process, electrodeposited precursor films are prepared at varying deposition bath temperatures, deposition currents, electrolyte concentrations, and deposition times. The films are annealed at about 550ºC in Se for 15 minutes and also by rapid thermal processing in flowing argon gas. The as-deposited and annealed films are characterized by inductively coupled plasma spectrometry and x-ray diffraction analysis.

Preparation and Properties of CdTe Films on Mo/Glass Substrates

AbstractShort-bandgap group II-VI compound cadmium telluride is widely used for the infrared optics, radiation detectors, and solar cells where p-type CdTe is needed. p-type conductivity of CdTe is mainly caused by the chlorine-based A-centers, and in part, by the less stable copper-oxygen complexes. As a rule, CdTe films are recrystallized by the help of a cadmium chloride flux that saturates CdTe with chlorine. In chlorine-saturated CdTe A-centers are converted to isoelectronic complexes that cause resistivity increasement of CdTe up to 9 orders of magnitude. Excess copper and oxygen or group I elements as sodium also deteriorate the p-type conductivity of CdTe like excess chlorine. p-type conductivity of CdTe can be restored e.g. by the vacuum annealing which removes excess chlorine from the film. Unfortunately, treatment that betters p-type conductivity of the CdTe film degrades the junction of the superstrate configuration cells. In this work we investigate possibilities to prepare p-type CdTe films on the molybdenum coated glass substrates. Samples were prepared by the vacuum evaporation and dynamic recrystallization of 6N purity CdTe on the top of Mo-coated glass substrates. Then samples were recrystallized with cadmium chloride flux under tellurium vapour pressure. Results of the test studies on the structure and electronic parameters of samples are presented and discussed.

Thin films formed by selenization of CuIn xB 1−x precursors in Se vapor

Previous attempts in producing light absorbing materials with bandgaps near the 1.37 eV efficiency optimum have included the partial substitution of gallium or aluminum for indium in the CIS system. The most efficient of these solar cells to date have had absorber layers with bandgaps<1.2 eV. It is logical that an even smaller substitutional atom, boron, should lead to a wider bandgap with a smaller degree of atomic substitution. In this study, copper–indium–boron precursor films are sputtered onto molybdenum coated glass substrates and post-selenized. In the selenized films, although X-ray diffraction (XRD) measurements confirm that a CIS phase is present, Auger electron spectroscopy (AES) results indicate that boron is no longer homogeneously dispersed throughout the film as it was in the case of the unselenized precursor.

CdTe Films on Mo/Glass Substrates: Preparation and Properties

AbstractShort-bandgap group II-VI compound cadmium telluride is widely used for the infrared optics, radiation detectors, and solar cells where p-type CdTe is needed. p-type conductivity of CdTe is mainly caused by the chlorine-based A-centers, and in part, by the less stable copperoxygen complexes. As a rule, CdTe films are recrystallized by the help of a cadmium chloride flux that saturates CdTe with chlorine. In chlorine-saturated CdTe A-centers are converted to isoelectronic complexes that cause resistivity increasement of CdTe up to 9 orders of magnitude. Excess copper and oxygen or group I elements as sodium also deteriorate the p-type conductivity of CdTe like excess chlorine. p-type conductivity of CdTe can be restored e.g. by the vacuum annealing which removes excess chlorine from the film. Unfortunately, treatment that betters ptype conductivity of the CdTe film degrades the junction of the superstrate configuration cells. In this work we investigate possibilities to prepare p-type CdTe films on the molybdenum coated glass substrates. Samples were prepared by the vacuum evaporation and dynamic recrystallization of 6N purity CdTe on the top of Mo-coated glass substrates. Then samples were recrystallized with cadmium chloride flux under tellurium vapour pressure. Results of the test studies on the structure and electronic parameters of samples are presented and discussed.

Composition and growth procedure-dependent properties of electrodeposited CuInSe 2 thin films

CuInSe 2 thin films were deposited on molybdenum-coated glass substrates by electrodeposition. Deposition was carried out with a variety of electrochemical bath compositions. The quality of the deposits depends very much on the source materials as well as the concentration of the same in the electrolyte. The deposition potential was varied from −0.4 to −0.75 V vs. SCE. The pH of the solution was adjusted to 1.5–2 using diluted sulphuric acid. Chloride salts containing bath yield good surface morphology, but there is always excess of the metallic content in the deposited films. Different growth procedures, like initial metallic layers of copper or indium, layers of copper selenide or indium selenide before the actual deposition of ternary chalcopyrite layers were attempted. Fabrication pathway, morphological and compositional changes due to the different precursor route has been analysed. The quality of the deposits prepared by one-step electrodeposition is better than the deposits with a two-stage process. The deposited films were characterized with XRD, SEM–EDAX, UV–visible spectroscopy and I– V characteristics. The deposited films were annealed in air as well as in nitrogen atmosphere. The influence of annealing temperature, environment and annealing time on the properties of the films are evaluated. Attempts were made to fabricate solar cell structure from the deposited absorber films. The structure of Mo/CuInSe 2/CdS/ZnO/Ni was characterized with surface, optical and electrical studies.