Preparation of CuInSe2 thin films through metal organic chemical vapor deposition method by using di-μ-methylselenobis(dimethylindium) and bis(ethylisobutyrylacetato) copper(II) precursors

Highly polycrystalline copper indium diselenide (CuInSe₂) thin films on molybdenum substrate were successfully grown at 330 °C through two-stage metal organic chemical vapor deposition (MOCVD) method by using two precursors at relatively mild conditions. First, phase pure InSe thin film was prepared on molybdenum substrate by using a single-source precursor, di-μ-methylselenobis(dimethylindium). Second, on this InSe/Mo film, bis(ethylisobutyrylacetato) copper(II) designated as Cu(eiac)₂ was treated by MOCVD to produce CuInSe₂ films. The thickness and stoichiometry of the product films were found to be easily controlled in this method by adjusting the process conditions. Also, there were no appreciable amounts of carbon and oxygen impurities in the prepared copper indium diselenide films.     

CuInSe2 thin films by d.c. and pulse-plated electrodeposition

CuInSe₂ thin films were prepared by electrodeposition from aqueous solution, containing CuSO₄, InCl₃ and SeO₂ under d.c. step pulse-voltage on d.c., and pulse-plating conditions. The films were characterized by scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. The influence of deposition technique on film composition, morphology and structure were studied. Heat treatment of pulse-plated films under vacuum resulted in the formation of CuInSe₂ with single-phase chalcopyrite structure.     

X-ray diffraction and compositional studies of AgInS2 thin films obtained by spray pyrolysis

Silver indium sulfide (AgInS₂) thin films have been prepared by the spray pyrolysis technique using silver acetate, indium acetate, and N,N-dimethylthiourea as precursor compounds. Depending on the film preparation conditions, AgInS₂ thin films are obtained which could be candidates to be used in photovoltaic devices. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) compositional studies were done on films formed at different substrate temperatures (T _s) and Ag:In:S ratios in the starting solutions. When Ag:In:S ratios are 1:1:1, 1:0.25:2, and 1:1:2, XRD patterns of the thin films indicated that the crystallographic structure is mainly chalcopyrite AgInS₂. An additional phase, acanthite Ag₂S, appeared when the depositions where done at low T _s. EDS analysis showed that AgInS₂ films near stoichiometric composition were obtained by using an atomic ratio of Ag:In:S = 1:1:2 in the starting solution and T _s = 400 °C.     

Nickel diffusion in polycrystalline CuInSe2 thin films with a <112> fiber texture

Nickel diffusion in CuInSe₂ thin films was studied in the temperature range 430-520 °C. Thin films of copper indium diselenide (CuInSe₂) were prepared by selenization of CuInSe₂-Cu-In multilayered structure on glass substrate. A thin film of Nickel was deposited and annealed at different temperatures. Surface morphologies of the Ni diffused and undiffused CuInSe2 films were investigated using scanning electron microscope. The alteration of Nickel concentration in the CuInSe₂ thin film was measured by Energy Dispersive X-Ray Fluorescence (EDXRF) technique. These measurements were fitted to a complementary error function solution and the diffusion coefficients at four different temperatures were evaluated. The diffusion coefficients of Ni in CuInSe₂ films were estimated from concentration profiles at temperatures 430-520 °C as D = 1.86 × 10^− 7(cm²s^− 1)exp[− 0.68(eV)/kT].     

Enhancing the performance of electrodeposited CuInSe2 solar cells by suppressing secondary phases using sodium dodecyl sulfate

CuInSe₂ thin films were prepared on Mo-coated glass substrates using pulse electrodeposition with an aqueous solution containing sodium dodecyl sulfate (SDS) as an additive. The effect of SDS on the electrochemistry mechanism that inhibits secondary phases (Cu_xSe_y) was examined using cyclic voltammetry, which indicated that SDS can inhibit the reduction of Cu²⁺ and H₂SeO₃ and prohibit the formation of secondary phases. Scanning electron microscopy and atomic force microscopy revealed that the cracks and roughness of CuInSe₂ films decreased considerably after adding SDS into the electrolyte. The suppression of secondary phases was also observed using X-ray diffraction and Raman spectroscopy. The optical bandgap values of the CuInSe₂ films were measured using a UV–vis–NIR spectrophotometer; the bandgap values of the films deposited in the electrolyte with 0 and 1 mM SDS were approximately 0.96 and 1.05 eV, respectively. As expected, based on these differences, the CuInSe₂ solar cell with the Al/AZO/i-ZnO/CdS/CuInSe₂/Mo/glass structure derived from precursor film deposited in an electrolyte containing SDS demonstrated greater efficiency (η = 2.51 %) than that of the cell derived from precursor film deposited in an electrolyte without SDS (η = 0.63 %).     

Synthesis and Optical Properties of CuInSe2 Films

The growth of CuInSe₂ films via evaporation from a compound source is studied by x-ray diffraction and x-ray fluorescence analysis. It is shown that, on heating, CuInSe₂ dissociates into copper and indium selenides, which partially vaporize before film deposition. At the beginning of the deposition process, the source consists mainly of Cu₂Se, CuInSe₂, and In₂Se₃ in different ratios, depending on the source temperature. During deposition, two phases vaporize for the most part: CuInSe₂ and In₂Se₃ or Cu₂Se and CuInSe₂, depending on the source temperature. As a result, some of the selenium, a highly volatile component, is lost, and the grown films consist of Cu₂Se _x (x 1), Se-deficient CuInSe₂, and InSe. At a source temperature of 1040°C, the impurity phases vaporize at approximately equal rates, and the grown films consist of CuInSe₂ only. During continuous heating of the source, all the decomposition products are transferred to the substrate, and the film is very close in composition to the source. The chemical composition and structure of the films are determined, and their optical absorption spectra are measured near the fundamental edge at 290 K. The absorption data are used to evaluate the band-structure parameters of CuInSe₂. A technique is proposed for assessing the band structure of this compound.     

Structural,optical, and electrical properties of flash-evaporated copper indium diselenide thin films

Copper indium diselenide (CuInSe₂) compound was synthesized by reacting its elemental components, i.e., copper, indium, and selenium, in stoichiometric proportions (i.e., 1:1:2 with 5% excess selenium) in an evacuated quartz ampoule. Structural and compositional characterization of synthesized pulverized material confirms the polycrystalline nature of tetragonal phase and stoichiometry. CuInSe₂ thin films were deposited on soda lime glass substrates kept at different temperatures (300–573 K) using flash evaporation technique. The effect of substrate temperature on structural, morphological, optical, and electrical properties of CuInSe₂ thin films were investigated using X-ray diffraction analysis (XRD), atomic force microscopy (AFM), optical measurements (transmission and reflection), and Hall effect characterization techniques. XRD analysis revealed that CuInSe₂ thin films deposited above 473 K exhibit (112) preferred orientation of grains. Transmission and reflectance measurements analysis suggests that CuInSe₂ thin films deposited at different substrate temperatures have high absorption coefficient (~10⁴ cm⁻¹) and optical energy band gap in the range 0.93–1.02 eV. Results of electrical characterization showed that CuInSe₂ thin films deposited at different substrate temperatures have p-type conductivity and hole mobility value in the range 19–136 cm²/Vs. Variation of energy band gap and resistivity of CuInSe₂ thin films deposited at 523 K with thickness was also studied. The temperature dependence of electrical conductivity measurements showed that CuInSe₂ film deposited at 523 K has an activation energy of ~30 meV.     

Structural and optical characterization of CuInSe2 films deposited by hot wall vacuum evaporation method

Copper indium diselenide (CuInSe₂) compound was prepared by direct reaction of high-purity elemental copper, indium and selenium. CuInSe₂ thin films were deposited onto well-cleaned glass substrates by a hot wall deposition technique using quartz tubes of different lengths (0.05, 0.07, 0.09, 0.11 and 0.13 m). X-ray diffraction studies revealed that all the deposited films are polycrystalline in nature and exhibit chalcopyrite structure. The crystallites were found to have a preferred orientation along the (1 1 2) direction. Micro-structural parameters of the films such as grain size, dislocation density, tetragonal distortion and strain have been determined. The grain sizes in the films were in the range of 65-250 nm. As the tube length increases up to 0.11 m the grain size in the deposited films increases, but the strain decreases. The film deposited using the 0.13 m long tube has smaller grain size and more strain. CuInSe₂ thin films coated using a tube length of 0.11 m were found to be highly crystalline when compared to the films coated using other tube lengths; it has also been found that films possess the same composition (Cu/In=1.015) as that of the bulk. Scanning electron microscope analysis indicates that the films are polycrystalline in nature. Structural parameters of CuInSe₂ thin films deposited under higher substrate temperatures were also studied and the results are discussed. The optical absorption coefficient of CuInSe₂ thin films has been estimated as 10⁴ cm⁻¹ (around 1050 nm). The direct band gap of CuInSe₂ thin films was also determined to be between 1.018 and 0.998 eV.     

Correlation between sprayed CuInSe2 thin films properties and deposition temperature

Copper indium diselenide thin films were prepared by spray pyrolysis technique on glass substrates at different deposition temperatures ranging from 150 to 300 °C. XRD patterns of sprayed CuInSe₂ films showed that all films are polycrystalline with a chalcopyrite structure and a preferential orientation along the (112) direction. The chemical composition analysis showed that the Cu/In ratio increased with increasing the deposition temperature. The atomic force micrographs show that the elaborated films have a uniform surface morphology with a homogeneous distribution of crystallites. The electrical conductivity of the prepared films increased with increasing the deposition temperature. The energy band gap of prepared films decreased with increasing Cu/In ratio.     

Effect of triethanolamine and sodium dodecyl sulfate on the formation of CuInSe2 thin films by electrodeposition

In this paper, we describe the development of a bath comprising triethanolamine and sodium dodecyl sulfate for electrodeposition of CuInSe₂ thin films, by which long-term bath stability was found to be improved and near-stoichiometric CuInSe₂ films with smooth surface morphology were obtained. Scanning electron microscopy studies reveal a dramatic improvement of the crystalline quality of CuInSe₂ films with the addition of sodium dodecyl sulfate. X-ray diffraction results and Raman spectra confirm that the improvement of the film growth is attributed to the synergistic effect of triethanolamine and sodium dodecyl sulfate. The addition of anionic surfactant sodium dodecyl sulfate can significantly improve the adherence between the CuInSe₂ layer and the substrate.     

Structural analysis of CuInSe2 thin films prepared by selenization of Cu-In films

This study involves the characterization of thin films of copper indium diselenide (CuInSe₂) deposited on soda-lime glass substrates using a two-step process. In this technique electron-beam-evaporated Cu-In precursor layers were reacted with an atmosphere containing H₂Se gas. The morphological and structural aspects of the CuInSe₂ layers were studied (by scanning electron microscopy and X-ray diffraction) as a function of the Cu-In film morphology and the selenization temperature profile and exposure time. It was found that the Cu-In precursor morphology has a significant influence on the structural properties of the final CuInSe₂ film. Selenization of the Cu-In alloys (irrespective of the structure considered) directly at high temperature resulted in films with poor structural properties. However, a vast improvement in the adhesion properties and morphology of the CuInSe₂ films were observed when the Cu-In films were exposed to a reactive selenium atmosphere while ramping the temperature between 150 C and 400 C. Selenization of triple-layer structures (Cu/In/Cu and In/Cu/In) resulted in films with good structural properties and excellent compositional uniformity.     

Composition and Morphology of Electrodeposited CuInSe2 Precursor Films

CuInSe₂ (CIS) precursor films have been prepared by electrodeposition in aqueous solution. The electrodeposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) for structural, morphological and componential properties. The influence of deposition potential and Na-citrate concentration on composition and morphology of electrodeposited films was studied in detail. It is found that the film morphology is strongly influenced by deposition potential and Na-citrate concentration. Films with large and homogenous grain size and ratio of Cu/In approaching 1 were obtained at deposition potentials of -0.7 and -0.75 V vs the saturated calomel electrode (SCE) and Na-citrate concentration of 500 mmol/L. Chalcopyrite phase CuInSe₂ is contained in precursor films that have poor crystallinity.     

Growth and characterization of CuInSe2 thin films prepared by successive ionic layer adsorption and reaction method with different deposition temperatures

CuInSe₂ films were prepared at different deposition temperatures (T_D) by successive ionic layer adsorption and reaction method with chelating solutions. Influence of T_D on film growth, morphology, crystal structure, and band gap energy was investigated. Results showed that elevation of T_D mainly enhanced reaction kinetics and ionic diffusion velocity, resulting in fast growth rate of CuInSe₂ films, and maximum 20-30 nm/cycle depended upon T_D were acquired. Films with 60 dip-cycles could grow from 180 nm to 1000 nm by elevating T_D from 30 °C to 90 °C. Surface roughness of CuInSe₂ films was closely related to dip-cycle times and T_D. Accelerated growth rate by T_D could reduce the dip-cycle times for a required film thickness, which improved quality of film morphology.     

Production of CuInSe2 thin films by a sequential processes of evaporations and selenization

Thin films of copper indium diselenide (CuInSe₂) were prepared by selenization of CuInSe₂-Cu-In multilayered structure on glass substrate. The selenization procedure was carried out in a vapour of elemental selenium in a vacuum chamber. The obtained films were characterised by XRD and SEM measurements. The effects of substrate temperature on the structural, electrical and optical properties were studied. It was found that single phase CuInSe₂ thin films with significant adhesion to substrate can be produced by selenization of CuInSe₂-Cu-In multilayered structure at 450°C, when the first non single phase CuInSe₂ layer was deposited at substrate temperature of 400°C. The thin films were found to be direct band gap semiconductors with a band gap of 0.97 eV.     

Spray pyrolysis of CuInSe2 and related ternary semiconducting compounds

CuInSe₂ and related compounds and alloys, which are promising for solar cell applications, were produced in thin polycrystalline sphalerite structure layers by spray pyrolysis in both p- and n-type forms with various resistivities. Complete sphalerite structure solid solution is indicated for the entire four-component system CuGaS₂-CuInS₂-CuInSe₂-CuGaSe₂ which suggests the possibility of tailoring properties such as lattice parameter, energy gap and conductivity type to produce heterojunctions suitable for low cost solar cells by spray pyrolysis.     

Formation of rod-crystals on CuInSe2 thin films by SILAR method using CH3-(CH2)11-C6H4-SO3Na surfactant

The formation of rod-crystals was observed on CuInSe₂ thin films prepared by successive ionic layer adsorption and reaction (SILAR) method using sodium dodecylbenzene sulfonate (SDBS) as directing agent. Rod-crystals appeared on the surface of CuInSe₂ thin film when adding SDBS into cationic precursor solution. FESEM, EDS, XRD and HRTEM were used to characterize the rod-crystals. The length of rod-crystals has a proportional relationship with SDBS amounts in the given scope of 0.001-0.01 mol/L. The stoichiometry of rod was close to 1:1:2 of CuInSe₂, and rod growth of partially preferential orientation along [112] was observed. The growth of rod could be explained by steric hindrance effects of SDBS adsorbed on the inorganic deposit surface.     

One-step electrodeposited CuInSe2 thin films studied by Raman spectroscopy

CuInSe₂ thin films one-step electrodeposited under different conditions were studied by MicroRaman spectroscopy to identify and quantify the individual phases present in the films.From the analysis of the Raman spectra, the main ternary phase (CuInSe₂) and elementary selenium Se⁰ were clearly identified. Specific chemical etches confirm the presence of elementary selenium Se⁰ and copper selenide binary phases Cu_xSe in selenium rich film.The amounts of these two phases were evaluated from X-ray Fluorescence measurements and confirmed using phase selective chemical treatments.     

Composition and structure of chemically deposited CulnSe2 thin films

The composition, morphology and crystallographic structure of CuInSe₂ films grown at 50°C and 90°C by the chemical method are discussed. Characterization includes EDS, X-ray and transmission electron diffraction and optical absorption spectroscopy. Nearly stoichiometric CuInSe₂ thin films are obtained with chalcopyrite structure and with thickness in the range 1–3 μm and the grain size in the range 0.2–1.5 μm, band gap near 0.9 eV and absorption coefficient α ≅ 10⁵ cm⁻¹.The effect of deposition mixture temperature on film orientation has been studied by X-ray and electron diffraction. Preferred orientation along [112] direction occurs at a deposition-mixture temperature of 90°C.     

Investigation of precursors concentration in spray solution on the optoelectronic properties of CuInSe2 thin films deposited by spray pyrolysis method

Copper indium selenide CuInSe₂(CISe) thin films were deposited by chemical spray pyrolysis (CSP) method of CuInS₂(CIS) and subsequent selenization process. To study the effects of solution concentration, we prepared different precursors solution of CIS including different amount of indium salts from 0.025 to 0.100 M with In/Cu 1.25 and S/In 4. These results propose that solution concentration is critical for inflecting the morphological, optical, electrical, and electrochemical characteristics of solution-processed CISe films and device performance. The studied morphological properties of deposited samples were homogenous, crack-free with large grains in indium salt concentrations more than 0.075 M. The deposited film thickness depends on the spray precursor concentration and increases for higher concentration. In addition with increasing of indium precursor concentration from 0.025 to 0.100 M in spray solution, the optical bandgap of deposited film decreases from 1.40 to 1.35 eV. Also the films mobility and carrier density were notably influenced by any change in the solution concentration. Electrical and electrochemical properties showed a decrease in carrier density from?~?10²⁰ to?~?10¹⁷ cm^?3 and the increase in mobility of order?~?10^–7 to?~?10^–2 cm²/V s, respectively, for 0.025 M, 0.100 M CISe films. All films exhibited p-type conductivity owing to different concentrations. However, it seems that the concentration of the ideal solution is 0.100 molars.

     

Investigation of chalcopyrite film growth at various temperatures: analyses from top to the bottom of the thin films

We reported a new method to investigate the phases and structures of thin film bottom parts. The films were polished by flapping papers to reach the bottoms. The surfaces and cross sections of thin films were observed by Scanning Electron Microscopy. Grazing Incidence X-ray Diffraction, Raman spectra and X-ray Photoelectron Spectroscopy (XPS) were used to investigate the phases, structures and chemical components of the surfaces and bottoms of thin films. By this method, we studied the growth processes of chalcopyrite films after the selenization at various temperatures from 270 to 600 °C. At 270 °C, a great amount of Cu–Se nodules formed at the surface, while (In,Ga)–Se stayed in the bottom. At 380 °C, a double layer structure was observed in the film. The top part was typical CuInSe₂ polycrystalline, while the bottom part contained complicated components, like CuInSe₂, Cu(In,Ga)₃Se₅, (In,Ga)Se. At 600 °C, a single layer was formed, which was composed of Cu(In,Ga)Se₂ phase. However, a higher Ga/(In+Ga) ratio was obtained towards the back contact. In addition, XPS indicated that the Mo/Cu(In,Ga)Se₂ interface was rich in Ga and Se.