Electrodeposited CuInSe2 Thin Films Research Articles

Composition Tuning of Single Step Electrodeposited CuInSe2 Thin Films Using Sodium Dodecyl Sulfate as Additive

CuInSe2 (CISe) thin films were electrodeposited on FTO substrates by single step deposition technique from an aqueous solution containing CuCl2, InCl3, HSeO3− ions and citric acid-sodium dodecyl sulfate (SDS) as the pH adjuster and additive, respectively. The effect of SDS concentration on the structural, composition, morphology and photo-electrochemical properties was characterized by SEM/EDAX, XRD, Raman and electrochemical (PEC) studies. The linear sweep voltammetry (LSV) and electrochemical impedance (EIS) results revealed that the addition of SDS limits the Cu-Se incubation time and enhances the diffusion controlled process which is considered to be the origin of the compositional and morphological tuning nature of the SDS in CISe deposition. The structural, compositional and PEC analysis revealed that for SDS concentration less the critical micelle concentration has almost no effect in controlling the Cu2Se secondary phase. The samples deposited in the presence of SDS (> 8 mM) exhibited better PEC properties due to the reduced Cu2Se phase. Further, the Mott–Schottky analysis of all the as-deposited thin films exhibited p-type conductivity.

Chemical bath composition effect on the properties of electrodeposited CuInSe2 thin films

Abstract Polycrystalline chalcopyrite CuInSe2 (CIS) thin films were deposited by electrodeposition technique onto ITO coated glass substrates. The used bath solution is formed by dissolution of CuCl2, InCl3, and SeO2 salts in de-ionized water, where the [Se]/[Cu + In] molar ratio is ranged from 0.4 to 1.3. The deposited films have been annealed at 300 °C for 30 min in argon atmosphere. The films structure and surface morphology characterizations were carried out respectively by means of X-ray diffraction method (XRD) and scanning electron microscope (SEM). XRD results indicate that CIS films having single phase chalcopyrite are obtained when the [Se]/[Cu + In] molar ratio is less than 1.3. While, for [Se]/[Cu + In] = 1.3, CuSe secondary phase is present together with CIS chalcopyrite phase. The crystallites were found to have a preferred orientation along (1 1 2) direction. The UV–visible optical transmittance measurements show that films absorption is due to allowed direct transition with a band gap ranged from 1.04 to 1.2 eV.

Continuous wave solid phase laser annealing of single-pot electrodeposited CuInSe2 thin films: Effects of Cu/In stoichiometry

CuInSe2 (CISe) is a prototype material for the I–III–VI chalcopyrites such as Cu(In,Ga)(S,Se)2 (CIGSSe) used as absorber layers in thin film photovoltaic cells. These thin film photovoltaic absorber layers are primarily synthesized by vacuum-based techniques in manufacturing. In this work, we investigate non-vacuum film synthesis by electrochemical deposition of CISe from a single bath followed by continuous wave laser annealing (CWLA) using a 1064 nm laser. We find that parameters exist for near-infrared CWLA which result in structural changes without melting and dewetting of the films. While Cu-poor samples show only about 40% reduction in the full width at half maximum (FWHM) of the respective x-ray diffraction (XRD) peaks, identically treated Cu-rich samples indicate a FWHM reduction of more than 70% in the XRD and Raman scattering data for irradiation at 50 W/cm2. This study demonstrates that an entirely solid-phase annealing path driven by intense illumination exists for chalopyrite phase formation and crystallization from electrodeposited CISe thin films.

Characterization of CuInSe2 thin films grown by photo-assisted electrodeposition

A photo-assisted one-step electrodeposition has been applied to help in forming smooth and dense CuInSe2 (CIS) films. The difference in surface morphology and crystalline quality between CIS films with and without photo-assistance has been investigated. In the photo-assisted electrodeposition process, a halogen lamp providing maximum light intensity at about 0.6μm–1.0μm was used as light source to be irradiated onto the surface of Mo-coated soda lime glass substrates. Electrodeposited CIS thin films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and Raman spectroscopy. SEM and AFM results show a smoother film with lower roughness by photo-assisted electrodeposition at lower deposition potential. From the XRD patterns, it was found that photo-assistance enhanced the crystalline quality, and the enhancement remained after annealing at 500°C for 120s. The analysis of Raman spectra indicated a reduction in secondary phases after applying photo-assistance. These results suggested effects of photo-assistance including activating surface diffusion and growing high-crystalline quality films with reduced defects during electrodeposition.

Growth and characterization of pulse electrodeposited CuInSe2 thin films

CuInSe2 thin films were grown on SnO2-coated glass substrates using the pulse electrodeposition (PED) technique. The CuInSe2 films were grown at different potentials using pulses of different frequencies ranging from 1 KHz to 1 MHz. The electrodeposited films were annealed in vacuum at 300°C, for 1 hr, to improve the crystallinity. The annealed films were characterized by x-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Analysis of x-rays (EDAX), and UV-VIS-NIR spectra. The results show that the electrodeposited CuInSe2 films have good stoichiometry and are single phase with an optical gap around 1 eV. SEM studies show that the films grown using pulses of frequency 1 KHz contain nanoparticles of size 50–60 nm, whereas those grown using pulses of frequency 100 KHz and 1 MHz contain micronsized particles.

The Linear Sweep Voltammetric Study and Two-Step Electrodeposition of CuIn<sub> 0.95</sub> Se<sub>2.1</sub>Thin Film in a Citric Acid Electrolyte

Electrodeposition of CuInSe2 (CIS) thin films has been investigated by linear sweep voltammetry on F-doped tin oxide (FTO) glass in electrolytes containing citric acid. It is found that one-step electrodeposited CIS thin films have great deviation from the ideal stoichiometric ratio. After deposited a film at -900 mV (vs.SCE) for 20s on the FTO, the linear sweep voltammetry has showed that only one reduction current peak at -550 mV is remained, and the two-step electrodeposited CIS film showed a near- toichiometric ratio of 1:0.9:2.1.

Preparation and characterization of pulse-plating electrodeposited CuInSe2 thin films

CuInSe2 thin films were electrodeposited on an indium-tin-oxide glass substrate by a pulse-plating technique from an aqueous electrolyte solution, containing CuSO4, InCl3 and SeO2 with the pH adjusted to 1.5 at room temperature. The deposited and heat-treated films were characterized structurally using X-ray diffraction (XRD), scanning electron microscopy (SEM) and auger electron spectroscopy (AES) analysis. The optical and the electrical properties of the films were also examined. When the film was submitted to heat-treatment above 300 ‡C in air for 1 h, the sample showed a chalcopyrite structure and n-type conductivity with a carrier concentration of ~ 1017 cm−3 and a band-gap (direct allowed transition) energy of 0.99 eV.

Photovoltaic activity of electrodeposited p-CuInSe2/electrolyte junction

The photovoltaic activity of electrodeposited CuInSe2 thin films in an aqueous acidic solution has been determined by photoelectrochemical measurements. We used the model of Gärtner to extract values of effective optoelectronic parameters of the CuInSe2 films. These values suggest the presence of a high density of bulk or surface defects in the electrodeposited layers.

ChemInform Abstract: Effects of Thermal and Chemical Treatments on the Composition and Structure of Electrodeposited CuInSe2 Thin Films.

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Effects of Thermal and Chemical Treatments on the Composition and Structure of Electrodeposited CuInSe2 Thin Films

thin films within a wide composition range have been obtained by a one‐step electrodeposition method onto molybdenum substrates. These films were then submitted to different postdeposition treatments: annealing in argon atmosphere and/or chemical etching in a 0.5M solution. The as‐grown and treated samples were examined by x‐ray diffraction for determination of crystalline quality and by chemical analysis for composition. Annealing improves the crystallinity of electrodeposited films; the effective grain size increased as the annealing temperature increased. Chemical etching produces significant changes in the film composition, the aqueous solution dissolves secondary phases of copper selenides that have been detected in the samples. Depending on the sequence of annealing and chemical treatments, the resulting thin films exhibit different characteristics.

Preparation and Characterization of Electrodeposited CuInSe2 Thin Films

CuInSe2 thin films were prepared on SnO2-coated glass by electrodeposition from aqueous solution containing CuCl2, InCl3 and SeO2. The deposition was carried out by varying cathode potential. It was found that the Cu/In ratio which influences CuInSe2 characteristics greatly can be controlled by the cathode potential. Annealing of as-deposited films in N2 atmosphere at 350°C was found to result in the formation of CuInSe2 films having a chalcopyrite structure. With the use of these annealed CuInSe2 thin films, CdS/CuInSe2 thin-film solar cells were formed as a preliminary step and the conversion efficiency of 1.49% was obtained.

Investigations of the electrical properties of electrodeposited CuInSe2 thin films

The electrical properties of as-grown and heat-treated copper indium diselenide (CuInSe2) thin films electrochemically deposited were measured in the temperature range 30 to about 300 K. In general the films showed variable range hopping conduction mechanism, i.e., σ= (σ0 T−1/2) exp[ − (T0/T)1/4] with T0 between 4 × 102 and 6 × 103 K, at the lowest temperatures, and thermally activated conductivity, i.e., σ = σ0 exp( − Ea/kT) with Ea between 240 and 80 meV, over the temperature range close to the room temperature. The activation energy, Ea, decreased and the conductivity, σ, increased with the annealing treatment. The data of these annealed films are in agreement with the Meyer–Neldel rule. Grain boundary trapping models were considered in the analysis of the results.

Growth and characterization of electrodeposited CuInSe2 thin films from seleno-sulphate solution

Ternary CuInSe2 thin films were prepared by electrodeposition from a high pH seleno-sulphate solution. The films were characterized by EDAX, X-ray diffraction and SEM. EDAX analysis shows that the stoichiometry of the films can be controlled by independently varying (i) the deposition current density, and (ii) the electrolytic bath composition. The films deposited at J=1.1 mA cm2 with InCl3 (15.12 mM) content in the bath mixture and at J=0.8 mA cm-2 with InCl3 (18.6 mM) content have a stoichiometric chalcopyrite structure with c/a approximately=1.97. Electrical measurements show that deposited films are p-type and have a resistivity of about 5*103 Omega cm.

Study of the optical transitions in electrodeposited CuInSe2 thin films

Optical absorption coefficients of electrodeposited CuInSe2 thin films were determined from the measured transmittance and reflectance at normal incidence of light in the wavelength range 400 to 2000 nm. As-deposited CuInSe2 is found to be a direct-gap semiconductor with an allowed direct transition whose gap energy is Ega= 0.96 eV and a forbidden direct transition whose gap energy is Egf= 1.38 eV. After heat treatment of the films at 400 °C, a decrease in the optical absorption was observed at energies below 1.1 eV. Heat-treated films showed an allowed direct transition with E′ga=1.00 eV, close to the value for as-deposited samples, but in this last case the forbidden direct transition was not observed.