Copper Indium Diselenide Thin Films Research Articles

Empirical investigation of the energy payback time for photovoltaic modules

Energy payback time is the energy analog to financial payback, defined as the time necessary for a photovoltaic panel to generate the energy equivalent to that used to produce it. This research contributes to the growing literature on net benefits of renewable energy systems by conducting an empirical investigation of as-manufactured photovoltaic modules, evaluating both established and emerging products. Crystalline silicon modules achieve an energy break-even in 3 to 4 years. At the current R&D pilot production rate (8% of capacity) the energy payback time for thin film copper indium diselenide modules is between 9 and 12 years, and in full production is ∼2 years. Over their lifetime, these solar panels generate 7 to 14 times the energy required to produce them. Energy content findings for the major materials and process steps are presented, and important implications for current research efforts and future prospects are discussed.

Pulsed excimer laser ablated copper indium diselenide thin films

CuInSe 2 thin films of thickness in the range of 0.45–1.8 μm were deposited on glass, Pt coated Si and Mo substrates by pulsed laser ablation at 150°C. Rapid thermal annealing (RTA) at a high heating rate was employed and its effect on crystallinity of the films was investigated. X-ray diffraction patterns of the RTA films, exhibited a highly preferred orientation along the (112) plane establishing the chalcopyrite structure. The composition of the as-grown and RTA films maintained the required stoichiometry ratios uniformly over a reasonable area. The EDAX composition analysis revealed that the films annealed at 500°C for 20 s were slightly indium rich, which consequently led the films to exhibit an n-type conductivity. However, RTA processing of the as-grown films at a higher temperature under controlled soaking time transformed the films to exhibit a p-type conductivity.

Electrochemical synthesis of CuInSe 2 for thin film devices

We have been investigating the materials properties and electrical characteristics of Schottky barriers on electrochemically deposited thin film copper indium diselenide (CIS). Electrochemical deposition is a simple and inexpensive technique of producing thin-film CIS. Stoichiometric control of the as-deposited films is provided by the deposition potential. Native defects, arising from stoichiometric deviations, have allowed the production of both p- and n-type CIS thin films from a single aqueous solution. We have compared the crystallinity, composition and electrical characteristics of as-deposited films to similar films annealed in an Argon atmosphere. The crystallinity showed a significant improvement with annealing. Current versus voltage measurements were used to verify the rectifying behavior of the Schottky barriers and determine their barrier heights. A decrease in the barrier height with increasing carrier density was observed. The capacitance versus voltage dependence of Al Schottky contacts was used to determine the carrier densities in the films. Carrier densities were found to increase with deviation from stoichiometry and decrease with annealing temperature.

Electrodeposited CdS on CIS pn junctions

We have been investigating the electrochemical deposition of thin films and junctions of cadmium sulfide (CdS) and copper indium diselenide (CIS). We show that it is possible to fabricate pn junctions based on n-type CdS and p-type CIS entirely by electrodeposition. CIS is considered to be one of the best absorber materials for use in polycrystalline thin-film photovoltaic solar cells. CdS provides a closely lattice-matched window layer for CIS. Electrodeposition is a simple and inexpensive method for producing thin-film CdS and CIS. We have produced both p- and n-type CIS thin films, as well as a CdS on CIS pn junction via electrodeposition. Elemental analysis of the CdS and CIS thin films was performed using X-ray photoelectron spectroscopy and energy dispersive spectroscopy. Optical band gaps were determined for these films using optical transmission spectroscopy. Carrier densities of the CIS films as a function of their deposition voltage were determined from capacitance vs. voltage measurements using Al Schottky barriers. Current vs. voltage characteristics were measured for the Al on CIS Schottky barriers and for the CdS on CIS pn junction.

Charge-carrier transport mechanism in copper indium di-selenide thin films

Thin films of copper indium di-selenide have been grown onto glass substrates by a stacked elemental layer (SEL) deposition technique in vacuum. The elemental composition of the films was ascertained by proton-induced x-ray emission (PIXE) spectroscopy. The electrical dc conductivity and the Hall coefficient of the films have been measured in the temperature range of -130 to +127 °C. The mode of transport of the charge carriers has been analysed. It is found that a multiple scattering effect is operative in the transport process.

Influence of heat treatment on the electrophysical properties of thin films of copper-indium diselenide

An investigation of the structural, electrical, optical, and thermophysical properties is carried out on thin polycrystalline films of the ternary semiconductor CuInSe2, which is potentially useful for fabricating solar cells. The thin films were obtained by thermal evaporation of CuInSe2 and Se powder from two independent sources and by high-vacuum deposition in a closed cell (quasiequilibrium deposition). The influence of annealing in air on the parameters of the thin films is analyzed, and the dynamics of variation in the properties of the films are investigated as a function of the annealing time. Temperature dependences of the electrical conductivity, mobility, and thermal conductivity of CuInSe2 thin films are given together with the spectral dependence of the short-circuit photocurrent of a photosensitive Au-CuInSe2-Au structure.

Electrodeposited CuInSe2 Thin Film Junctions

ABSTRACTWe have investigated thin films and junctions based on copper indium diselenide (CIS) which have been grown by electrochemical deposition. CIS is a leading candidate for use in polycrystalline thin film photovoltaic solar cells. Electrodeposition is a cost-effective method for producing thin-film CIS. We have produced both p and n type CIS thin films from the same aqueous solution by simply varying the deposition potential. A CIS pn junction was deposited using a step-function potential. Stoichiometry of the single layer films was determined by energy dispersive spectroscopy. Carrier densities of these films increased with deviation from stoichiometry, as determined by the capacitance versus voltage dependence of Schottky contacts. Optical bandgaps for the single layer films as determined by transmission spectrocopy were also found to increase with deviation from stoichiometry. Rectifying current versus voltage characteristics were demonstrated for the Schottky barriers and for the pn junction.

Reproducibility studies on thin-film copper indium diselenide prepared from copper indium oxide

Thin-film copper indium diselenide was prepared by selenization of copper indium oxide deposited by spray pyrolysis of an aqueous solution containing copper and indium salts. The degree of reproducibility in thickness, composition and electrical parameters was found to be good. The electrical parameters could be controlled and tuned for photovoltaic applications reproducibly by means of this cost-efficient fabrication technique.

Growth and Characterization of Copper Indium Diselenide Thin Films by Molecular Beam Deposition

AbstractCuInSe2 thin films grown on Corning 7059 glass substrates were prepared by molecular beam deposition method with various Cu/In ratios in order to study the relationship between composition and material properties. Under a fixed copper beam flux intensity and overpressure selenium environments, the composition of films was modulated by changing the indium beam flux: intensity to obtain Cu-rich or In-rich films. The X-ray diffraction patterns show that the epitaxy films grown onto glass substrates are the polycrystalline structure. The grain size of polycrystalline films indicate that the surface morphology of the films are varied as a function of Cu/In ratio.

Thin-film copper indium diselenide prepared by selenization of copper indium oxide formed by spray pyrolysis

Thin-film copper indium diselenide (CIS) was prepared by a process which involves two steps: (a) the formation of copper indium oxide by spray pyrolysis of an aqueous solution, and (b) subsequent reaction of the oxide with selenium vapour to form CIS. This technique provided oxide and selenide films with good purity and uniformity. During the oxide film formation two film growth mechanisms could be observed. The deposition efficiency of the spray pyrolysis step was rather high and dependent on the spray parameters, and a slight preference for Cu was observed. Conversion of the oxide film to the selenide caused an increase in film thickness and a further loss of indium. The resulting specular CIS films were soft and adhered well to the substrate. Conductivity and carrier type and density could be varied by control of the composition of the film.

Copper indium diselenide single-crystal and thin-film infrared sensors

Copper indium diselenide (CIS) and copper indium gallium diselenide (CIGS) are now well established as exceptionally efficient semiconductors with potential applications in the fields of solar cells, infrared radiation monitors and fibre optic infrared detectors. CIGS can be doped both p- and n-type and has a direct band gap which can be varied between 1.02 eV and 1.68 eV. Single-crystal CIS infrared detectors were produced on p-type substrates. The devices displayed photosensitivity significantly superior to that of silicon in the infrared at wavelengths up to 1.3 μm. Thin films were deposited by pulsed laser ablation of polycrystalline CIS targets using a XeCl excimer laser. The electrical and photo response of the thin film devices, while inferior to that from single crystals, indicated that laser ablated thin-film CIS sensors have potential for use as infrared detectors.

Solar cells with improved efficiency based on electrodeposited copper indium diselenide thin films

Solar cells based on CuInSe2 (CIS) thin films prepared as described in the previous contribution have been prepared and characterized. The light and dark current–voltage curves and spectral responses are presented, showing that annealing in a selenium atmosphere makes it possible to fabricate ZnO/CdS/CIS solar cells with improved efficiencies. CIS is of particular interest because its optical properties are well matched to the solar spectrum.

Electrochemical preparation and characterization of copper indium diselenide thin films

Thin polycrystalline CuInSe 2 films were cathodically deposited on titanium and SnO 2 coated glass at potentials ranging from −350 mV to −750 mV vs SCE from aqueous sulphate bath using citric acid as complexing agent. The films were annealed at 425°C in an argon atmosphere and characterised by X-ray diffraction and EPMA. From the XRD analysis the structure of the film was found to be tetragonal. The composition of the as deposited film was found to be 1:1:2 by EPMA. From the optical studies the band gap was found to be 1.02 eV. All the as deposited films were found to be p-type. On post heat treatment at 425°C the films deposited at or above −650 mV changed to n-type whereas below −650 mV p-type films only were obtained.