Effect of bath temperature and annealing on the formation of CuInSe2

CuInSe₂ films of 2 μm thickness were electrodeposited potentiostatically, from aqueous solution containing thiocyanate as a complexing agent, on Mo substrates. For all the experiments, the potential of the potentiostatic deposition of the materials was chosen to be −1 V, whereas the bath temperature of electrolyte was varied from 20 to 80 °C. It was found that the electrodeposited CuInSe₂ was characterized by an amorphous layer and densely-packed nanometric grains with a good homogeneity. After vacuum annealing at 200 °C, glancing angle X-ray diffraction revealed the presence of the CuInSe₂ phase whereas annealing under selenium atmosphere lead to the growth of molybdenum selenide compound MoSe₂, in addition to a better crystallization of the copper indium diselenide compound. Scanning electron microscopic revealed that despite an increase in the grains dimensions, there was no significant change in the films surface morphology when the bath temperature was varied from 20 to 80 °C. At the same time, the composition of the electrodeposited Cu-In-Se layers becomes richer in copper. This increase in copper concentration is mainly compensated by a deficit in selenium atoms.     

Sub-micrometer thick CuInSe2 films for solar cells using sequential elemental evaporation

CuInSe₂ thin films were prepared using sequential vacuum evaporation of In, Se and Cu at moderately low substrate temperatures, avoiding any treatment using toxic H₂Se gas. The samples were annealed at 400 °C at a pressure of 10⁻⁵ mbar to form CuInSe₂. Structural, optical, electrical, compositional and morphological characterizations were carried out on these films. We could obtain highly stoichiometric film, using this simple method, without opting for co-evaporation or high substrate temperature for deposition.     

Preparation of Cu(In,Ga)(S,Se)2 thin films by sequential evaporation and annealing in sulfur atmosphere

Cu(In,Ga)(S,Se)₂ thin films with high Ga/III ratio (around 0.8) were prepared by sequential evaporation from CuGaSe₂, CuInSe₂, In₂Se₃ and Ga₂Se₃ compounds and then annealing in H₂S gas atmosphere. The annealing temperature was varied from 400 to 500 °C. These samples were characterized by means of XRF, EPMA, XRD and SEM. The S/(S+Se) mole ratio in the thin films increased with increase in the annealing temperature, keeping the Cu, In and Ga contents nearly constant. The open circuit voltage increased and the short circuit current density decreased with increase in the annealing temperature. The best solar cell using Cu(In,Ga)(S,Se)₂ thin film with Ga/(In+Ga)=0.79 and S/(S+Se)=0.11 annealed at 400 °C demonstrated V_oc=535 mV, I_sc=13.3 mA/cm², FF=0.61 and efficiency=4.34% without AR-coating.     

Fabrication of CuInSe2 films and solar cells by the sequential evaporation of In2Se3 and Cu2Se binary compounds

Cu₂Se/In_xSe(x≈1) double layers were prepared by sequentially evaporating In₂Se₃ and Cu₂Se binary compounds at room temperature on glass or Mo-coated glass substrates and CuInSe₂ films were formed by annealing them in a Se atmosphere at 550°C in the same vacuum chamber. The In_xSe thickness was fixed at 1 μm and the Cu₂Se thickness was varied from 0.2 to 0.5 μm. The CuInSe₂ films were single phase and the compositions were Cu-rich when the Cu₂Se thickness was above 0.35 μm. And then, a thin CuIn₃Se₅ layer was formed on the top of the CuInSe₂ film by co-evaporating In₂Se₃ and Se at 550°C. When the thickness of CuIn₃Se₅ layer was about 150 nm, the CuInSe₂ cell showed the active area efficiency of 5.4% with V_oc=286 mV, J_sc=36 mA/cm² and FF=0.52. As the CuIn₃Se₅ thickness increased further, the efficiency decreased.     

Investigation of the chalcogen interdiffusion in CuIn(TeSe)2 thin films

Graded thin films of CuInSe₂ on CuInTe₂ have been obtained by annealing of precursor structures containing Se and Te separated in depth. The depth profile of the phases in the film was investigated using X-ray diffraction with grazing incidence of the primary beam. Quasi-epitaxial growth of CuInSe₂ on a CuInTe₂ film next to the Mo back-electrode was observed after annealing at 450°C in vacuum. Annealing at higher temperature lead to chalcogen interdiffusion resulting in quaternary films. However, heat treatments of already reacted films did not result in any detectable interdiffusion. From these results the mechanisms governing the growth of films from precursors containing the chalcogens Se and Te separated in depth are discussed with respect to their application for thin film solar cells.     

Optical, electrical and structural properties of indium-doped cadmium oxide films obtained by the sol-gel technique

Indium-doped cadmium oxide films were obtained by mixing cadmium oxide and indium oxide precursor solutions by the sol-gel technique. The indium atomic concentrations in solution (x) studied were 0, 2, 5 and 10 at%. The films were sintered at two different sintering temperatures (T_s) 350 and 450 °C, and after that annealed in a 96:4 N₂/H₂ gas mixture atmosphere at 350 °C. X-ray diffraction patterns showed that all films sintered at T_s=350 °C only consisted of cadmium oxide crystals. The films sintered at T_s=450 °C consisted of cadmium oxide crystals also; however, for the highest indium atomic concentration (10 at%) the formation of cadmium indate oxide crystals was evident. All films show high optical transmission (>85%) and an increase of the direct band gap value from 2.4 to 3.1 eV, as the indium atomic concentration in solution increases. The minimum resistivity value obtained was 6.3×10⁻⁴ Ω cm for the films with x=5 at%, T_s=450 °C and annealed at 350 °C.     

Study of phases formed during production of copper indium diselenide by reacting copper, indium and selenium layers

CuInSe₂ films were grown by reacting stacked layers of Cu, In and Se in an atmosphere of Se vapor. Incremental growth of the various phases was followed at different temperatures until a single phase CuInSe₂ film was formed. Conventional X-ray diffraction was used in identifying the different phases formed. Along with the knowledge of different phases formed at increasing reaction temperatures, it was concluded that CuInSe₂ is formed at temperatures as low as 235°C, although a single phase film is obtained only at higher temperatures (≈350°C).     

An investigation into effect of cationic precursor solutions on formation of CuInSe2 thin films by SILAR method

SILAR deposition of CuInSe₂ films was performed by using Cu²⁺–TEAH₃ (cupric chloride and triethanolamine) and In³⁺–CitNa (indium chloride and sodium citrate) chelating solutions with weak basic pH as well as Na₂SeSO₃ solution at 70 °C. A separate mode and a mixed one of cationic precursor solutions were adopted to investigate effects of the immersion programs on crystallization, composition and morphology of the deposited CuInSe₂ films. Chelating chemistry in two solution modes was deducted based on IR measurement. The XRD, XPS and SEM results showed that well-crystallized, smoothly and distinctly particular CuInSe₂ films could be obtained after annealing in Ar at 400 °C for 1 h by using the mixed cationic solution mode.     

TiO2 thin films - Influence of annealing temperature on structural, optical and photocatalytic properties

Nanostructured TiO₂ thin films were deposited on glass substrates by sol-gel dip coating technique. The structural, morphological and optical characterizations of the as deposited and annealed films were carried out using X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), and UV-vis transmittance spectroscopy. As-deposited films were amorphous, and the XRD studies showed that the formation of anatase phase was initiated at annealing temperature close to 400 °C. The grain size of the film annealed at 600 °C was about 20 nm. The lattice parameters for the films annealed at 600 °C were a = 3.7862 ? and c = 9.5172 ?, which is close to the reported values of anatase phase. Band gap of the as deposited film was estimated as 3.42 eV and was found to decrease with the annealing temperature. At 550 nm the refractive index of the films annealed at 600 °C was 2.11, which is low compared to a pore free anatase TiO₂. The room temperature electrical resistivity in the dark was of the order of 4.45 × 10⁶ ohm-cm. Photocatalytic activity of the TiO₂ films were studied by monitoring the degradation of aqueous methylene blue under UV light irradiation and was observed that films annealed above 400 °C had good photocatalytic activity which is explained as due to the structural and morphological properties of the films.     

Thin films of CuInSe2 prepared by RF sputtering from various compositional powder targets

CuInSe₂ thin films were prepared in the temperature range of 300–500°C by RF sputtering from powder targets, which were previously synthesized by reacting Cu, In, and Se in various ratios. The peaks from X-ray diffraction analyses were assigned to the planes of the CuInSe₂ chalcopyrite structure. The full width at half maximum of the (112) diffraction peak decreased with an increase in Cu/In ratio in the thin films. The photoelectron energies of the prepared thin films agreed with those reported for single crystalline CuInSe₂ from X-ray photoelectron spectroscopy measurements. The electronic conduction type and optical properties were found to change according to the Cu/In ratio in the thin films.     

Three-stage growth of Cu–In–Se polycrystalline thin films by chemical spray pyrolysis

Structural, optical and electrical properties of polycrystalline Cu–In–Se films, such as CuInSe₂ and ordered vacancy compounds (OVC), prepared by three-stage process of sequential chemical spray pyrolysis (CSP) of In–Se (first stage), Cu–Se (second stage) and In–Se (third stage) solutions have been studied in terms of substrate temperature at the second stage (T_S2). The films grown at T_S2420 °C exhibited larger grains in comparison with the Cu–In–Se films grown by the usual CSP method. Optical gap energy was approximately 1.06 eV for 360 °CT_S2420 °C, but increased dramatically from 1.06 to 1.35 eV when the T_S2 rose from 420 to 500 °C. Conductivity type was p-type for T_S2<420 °C, but n-type for T_S2>420 °C.     

Characterization of co-sputtered Cu-In alloy precursors for CuInSe2 thin films fabrication by close-spaced selenization

Sputtering technique for Cu–In precursor films fabrication using different Cu and In layer sequences have been widely investigated for CuInSe₂ production. But the CuInSe₂ films fabricated from these precursors using H₂Se or Se vapour selenization mostly exhibited poor microstructural properties. The co-sputtering technique for producing Cu–In alloy films and selenization within a close-spaced graphite box resulting in quality CuInSe₂ films was developed. All films were analysed using SEM, EDX, XRD and four-point probe measurements. Alloy films with a broad range of compositions were fabricated and XRD showed mainly In, CuIn₂ and Cu₁₁In₉ phases which were found to vary in intensities as the composition changes. Different morphological properties were displayed as the alloy composition changes. The selenized CuInSe₂ films exhibited different microstructural properties. Very In-rich films yielded the ODC compound with small crystal sizes whilst slightly In-rich or Cu-rich alloys yielded single phase CuInSe₂ films with dense crystals and sizes of about 5 μm. Film resistivities varied from 10⁻²–10⁸ Ω cm. The films had compositions with Cu/In of 0.40–2.3 and Se/(Cu+In) of 0.74–1.35. All CuInSe₂ films with the exception of very Cu-rich ones contained high amount of Se (>50%).     

Growth, structural and optical properties of copper indium diselenide thin films deposited by thermal evaporation method

Copper indium diselenide (CuInSe₂) compound was synthesized by reacting its constituent’s elements copper, indium and selenium in near stoichiometric proportions (i.e. 1:1:2 with 5% excess selenium) in an evacuated quartz ampoule. Synthesized pulverized compound material was used as an evaporant material to deposit thin films of CuInSe₂ onto organically cleaned sodalime glass substrates, held at different temperatures (300-573 K), by means of single source thermal evaporation method. The phase structure and the composition of chemical constituents present in the synthesized compound and thin films have been investigated using X-ray diffraction and energy dispersive X-ray analysis, respectively. The investigations show that CuInSe₂ thin films grown above 423 K are single phase, having preferred orientation of grains along the (112) direction, and having near stoichiometric composition of elements. The surface morphology of CuInSe₂ films, deposited at different substrate temperatures, has been studied using the atomic force microscopy to estimate its surface roughness. An analysis of the transmission spectra of CuInSe₂ films, recorded in the wavelength range of 500-1500 nm, revealed that the optical absorption coefficient and the energy band gap for CuInSe₂ films, deposited at different substrate temperatures, are ∼10⁴ cm⁻¹ and 1.01-1.06 eV, respectively. The transmission spectrum was analyzed using iterative method to calculate the refractive index and the extinction coefficient of CuInSe₂ thin film deposited at 523 K. The Hall effect measurements and the temperature dependence of the electrical conductivity of CuInSe₂ thin films, deposited at different substrate temperatures, revealed that the films had electrical resistivity in the range of 0.15-20 ohm cm, and the activation energy 82-42 meV, both being influenced by the substrate temperature.     

The structural and material properties of CuInSe2 and Cu(In,Ga)Se2 prepared by selenization of stacks of metal and compound precursors by Se vapor for solar cell applications

CuInSe₂ films and related alloys were prepared by thermal evaporation of Cu, InSe and GaSe compounds instead of elemental sources. Band-gap tailoring in Cu(In,Ga)Se₂-based solar cells is an interesting path to improve their performance. In order to get comparable results, solar cells with Ga/(In+Ga) ratios x=0 and 0.3 were prepared, all with a simple two-step sequential evaporation process. The morphology of the resulting films grown at 550 °C was characterized by the presence of large facetted chalcopyrite grains, which are typical for device quality material. It is important to note that absorber films with elemental gallium resulted in a significant decrease in the average grain size of the film. The X-ray diffraction (XRD) diffraction pattern of single-phase Cu(In,Ga)Se₂ films depicts diffraction peaks shifting to higher 2θ values compared to that of pure CuInSe₂. The photoluminiscence (PL) spectrum of Cu(In,Ga)Se₂ thin films also depicts the presence of the peak at higher energy that is attributed to the incorporation of gallium into the chalcopyrite lattice. As the band gap of CIGS increases with gallium content, desirable effects of producing higher open-circuit voltage and low current density devices were achieved. A corresponding increase in device efficiency with gallium content caused by a higher fill factor was observed. The best results show passive area efficiencies of up to 10.2% and open-circuit voltage (V_oc) up to 519 mV at a minimum band gap of 1.18 eV.     

Effect of selenization pressure on CuInSe2 thin films selenized using co-sputtered Cu-In precursors

CuInSe₂ thin films were formed from the selenization of co-sputtered Cu–In alloy layers. These layers consisted of only two phases, CuIn₂ and Cu₁₁In₉, over broad Cu–In composition ratio. The concentration of Cu₁₁In₉ phase increased by varying the composition from In-rich to Cu-rich. The composition of co-sputtered Cu–In alloy layers was linearly dependent on the sputtering power of Cu and In targets. The metallic layers were selenized either at a low pressure of 10 mTorr or at 1 atm Ar. A small number of Cu–Se and In–Se compounds were observed during the early stage of selenization and single-phase CuInSe₂ was more easily formed in vacuum than at 1 atm Ar. Therefore, CuInSe₂ films selenized in vacuum showed smoother surface and denser microstructure than those selenized at 1 atm. The results showed that CuInSe₂ films selenized in vacuum had good properties suitable for a solar cell.     

Ba0.5Sr0.5Co0.8Fe0.2O3 − δ + LaCoO3 composite cathode for Sm0.2Ce0.8O1.9-electrolyte based intermediate-temperature solid-oxide fuel cells

A novel Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ + LaCoO₃ (BSCF + LC) composite oxide was investigated for the potential application as a cathode for intermediate-temperature solid-oxide fuel cells based on a Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte. The LC oxide was added to BSCF cathode in order to improve its electrical conductivity. X-ray diffraction examination demonstrated that the solid-state reaction between LC and BSCF phases occurred at temperatures above 950 °C and formed the final product with the composition: La_0.316Ba_0.342Sr_0.342Co_0.863Fe_0.137O_3 − δ at 1100 °C. The inter-diffusion between BSCF and LC was identified by the environmental scanning electron microscopy and energy dispersive X-ray examination. The electrical conductivity of the BSCF + LC composite oxide increased with increasing calcination temperature, and reached a maximum value of ∼300 S cm⁻¹ at a calcination temperature of 1050 °C, while the electrical conductivity of the pure BSCF was only ∼40 S cm⁻¹. The improved conductivity resulted in attractive cathode performance. An area-specific resistance as low as 0.21 Ω cm² was achieved at 600 °C for the BSCF (70 vol.%) + LC (30 vol.%) composite cathode calcined at 950 °C for 5 h. Peak power densities as high as ∼700 mW cm⁻² at 650 °C and ∼525 mW cm⁻² at 600 °C were reached for the thin-film fuel cells with the optimized cathode composition and calcination temperatures.     

A superstrate solar cell based on In2(Se,S)3 and CuIn(Se,S)2 thin films fabricated by electrodeposition combined with annealing

Stacked thin films composed of In₂(Se,S)₃ and CuIn(Se,S)₂ layers were grown on a fluorine-doped tin oxide (FTO)-coated glass substrate using electrodeposition of the corresponding selenide (In₂Se₃ and CuInSe₂) precursors followed by annealing in H₂S flow (5% in Ar). Structural characterizations of both layers revealed that the resulting film quality strongly depended on annealing conditions of both CuIn(Se,S)₂ and In₂(Se,S)₃ layers: a compact and uniform film was obtained by annealing both layers at 400 °C. Performance of Au/CuIn(Se,S)₂/In₂(Se,S)₃/FTO superstrate-type solar cells also followed these structural characteristics, i.e., a preliminary conversion efficiency of 2.9% was obtained on the device based on 400 °C-annealed In₂(Se,S)₃ and CuIn(Se,S)₂ layers.     

Synthesis and characterization of nanosized LiNiVO4 electrode material

Inverse spinel LiNiVO₄ thin films were prepared by rf-sputtering, fallowed by films annealed at 300, 450 and 600 °C for 2 h to induce the crystallization of the films. The films were characterized by X-ray diffraction, Rutherford backscattering spectroscopy, nuclear reaction analysis, Auger electron spectroscopy, atomic force microscopy and scanning electron microscope techniques. The Anodic electrochemical performance films have been cycled in the range of 0.02–3.0 V, at room temperature, at a current density 75 μA cm⁻². Galvanostatic cycling and cyclic voltammetry results shows characteristic cycling curves with respect to annealing temperature. The films annealed at 450 °C showed best electrochemical performance and excellent capacity retention during cycling was observed due to its nanosized morphology.     

Preparation and study of structural and optical properties of CSVT deposited CuInSe2 thin films

A simple close-spaced vapour transport (CSVT) system has been designed and fabricated. Copper indium diselenide (CuInSe₂) thin films of wide range of thickness (4000–60000 Å) have been prepared using the fabricated CSVT system at source temperatures 713, 758 and 843 K. A detailed study on the deposition temperature has been made and the temperature profile along with the reaction kinetics is reported. The composition of the chemical constituents of the films has been determined by energy dispersive X-ray analysis. The structural characterization of the as-deposited CuInSe₂ films of various thicknesses has been carried out by X-ray diffraction method. The diffractogram revealed that the CuInSe₂ films are polycrystalline in nature with chalcopyrite structure. The structural parameters such as lattice constants, axial ratio, tetragonal distortion, crystallite size, dislocation density and strain have been evaluated and the results are discussed. The surface morphology of the as-deposited CuInSe₂ thin films has been studied using scanning electron microscope. The transmittance characteristics of the CuInSe₂ films have been studied using double beam spectrophotometer in the wavelength range 4000–15000 Å and the optical constants n and k are evaluated. The absorption coefficient has been found to be very high and is of the order of 10⁵–10⁶ m⁻¹. CuInSe₂ films are found to have a direct allowed transition and the optical band gap is found to be in the range 0.85–1.05 eV.     

Effects of substrate temperature on the structural and electrical properties of Cu(In,Ga)Se2 thin films

Polycrystalline Cu(In,Ga)Se₂ (CIGS) thin films were deposited onto soda-lime glass substrates using the three-stage process at the substrate temperature (T_sub) varying from 350 to 550 °C. The effect of T_sub on the structural and electrical properties of CIGS films has been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Hall effect measurement. We found that the surface roughness, constituent phases, film morphologies, resistivity (ρ) and carrier concentration (N_P) of as-grown CIGS films indicated different change trends with increase in T_sub. The higher T_sub gives smooth surface, large grain size and single-phase CIGS films. The values of N_P and ρ have two demarcated regions at T_sub of 380 and 450 °C. At lower T_sub of 380 °C, larger N_P and lower ρ were dominated by the existence of secondary-phase Cu_xSe with lower resistivity. In the case of 450 °C, the obvious changes in N_P and ρ can be attributed to the sufficient Na incorporation diffused from the glass substrate. Finally, the correlation of cell parameters with T_sub was analyzed.