Thin CuInS Research Articles

Influence of laser wavelength on the laser induced breakdown spectroscopy measurement of thin CuIn 1− xGaxSe2 solar cell films

Laser induced breakdown spectroscopy (LIBS) measurement of thin CuInxGa1−xSe2 (CIGS) films (1.2–1.9μm) with varying Ga to In ratios was carried out using the fundamental (1064nm) and second harmonic (532nm) wavelength Nd:YAG lasers (τ=5ns, spot diameter=150μm, top-hat profile) in air. The concentration ratios of Ga to In, xGa≡Ga/(Ga+In), of the CIGS samples ranged from 0.027 to 0.74 for which the band gap varied nearly proportionally to xGa from 0.96 to 1.42. It was found that the LIBS signal of 1064nm (1.17eV) wavelength laser was significantly influenced by xGa, whereas that of the 532nm (2.34eV) laser was consistent for all values of xGa. The observed dependency of the LIBS signal intensity on the laser wavelength was attributed to the large difference of photon energy of the two wavelengths that changed the absorption of incident laser energy by the film. The 532nm wavelength was found to be advantageous for multi-shot analysis that enabled depth profile analysis of the thin CIGS films and for improving measurement precision by averaging the multi-shot LIBS spectra.

Epitaxial and polycrystalline CuInS 2 thin films: A comparison of opto-electronic properties

Epitaxial and polycrystalline thin CuInS 2 (CIS) layers were grown by means of molecular beam epitaxy (MBE) on single crystalline silicon substrates of 4 inch diameter. Photoluminescence (PL) studies were performed to investigate the opto-electronic properties of these layers. For the epitaxial CIS, low-energy-hydrogen implantation leads to the passivation of deep defects and several donor–acceptor (DA) pair recombinations (from 1.034 eV to 1.439 eV) and two free-to-bound (FB) transitions (at 1.436 eV and 1.485 eV) become observable at low temperatures (5 to 100 K). Excitonic luminescence is completely absent for all investigated epitaxial CIS layers. This contrasts sharply with the PL of the polycrystalline films which is dominated by excitonic luminescence (1.527 eV). Also a donor-to-valence band transition at 1.465 eV (BF-1) and one donor–acceptor recombination at 1.435 eV (DA-1) were observed, while luminescence from deep levels is not present at all. Based on these data, a refined defect model for CuInS 2 with two donor and two acceptor states is presented. Under comparable growth conditions, the electronic quality of polycrystalline CIS is superior to epitaxially grown material.

Preparation and properties of CuInS 2 thin film prepared from electroplated precursor

Thin CuInS 2 films were prepared by sulfurization of Cu/In bi-layers. First, the precursor layer was electroplated onto the treated surface of Mo-coated glass. Observation of the cross-section prepared by focused ion beam (FIB) etching revealed that the void-free film was initially formed on the top surface of the precursor layer and continued to grow until the advancing front of the film reached the Mo layer. The nucleation of voids near the bottom of the CuInS 2 film followed. To determine whether the condition of the Cu/In alloy influences the CuInS 2 quality we investigated the Cu/In alloy state using FIB. We found that the annealed precursor of low Cu/In ratio (1.2) has several voids in the mid position in the layer compared with Cu-rich precursor (1.6). The cross-sectional view of the Cu-rich absorber layer is uniform compared with the low copper absorber layer. Thin film solar cells were fabricated using the CuInS 2 film (Cu/In ratio: 1.2) as an optical absorber layer. It was found that the optimization of a sulfurization period is important in order to improve the cell efficiency. We have not yet obtained good results with high Cu-rich absorber because of a blister problem. This blister was found before sulfurization. So, we are going to solve this blister problem before sulfurization.

Thin CuInS2 Films Prepared by MOMBE: Interface and Surface Properties

AbstractCuInS2 films were prepared on Si(111) by MOMBE using standard MBE Cu and In sources and Ditertbutyldisulfide (TBDS) as an organic sulfur precursor. The films were analyzed in situ by XPS, LEED and UPS. Deposition at 250°C yields chalcopyrite films [1] with admixtures of CuSi2 and CuIn alloys. Deposition at higher temperatures up to 550°C was used to clarify the feasibility of the process. High quality LEED diffraction patterns show epitaxial growth but CuSi2 precipitations are still observed for deposition on Si(111). A buffer layer of indiumsulfide showed no considerable effect on the interface morphology. The obtained LEED pattern are in accordance with the epitaxial relation Si{111}||CuInS2{112}. Even for temperatures as high as 550°C no incorporation of Carbon or residual hydrocarbons in the film or adsorbed at the surface were detected.

Effects of Na incorporation in CuInS2thin films

The incorporation of the doping element Na as well as the impact of this element on the structural, morphological and optical properties of evaporated CuInS 2 films on Corning 7059 glass substrates is studied. The element Na was evaporated from a thermal evaporation source. The amount of the Na source was determined to be 0–1 at.% compared with CuInS 2 source. The substrate temperature was maintained at 200 °C. The effects of Na on films properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical transmittance and reflectance spectra. SEM observation revealed the increase of the surface crystallinity and an enhancement of surface grain size with Na doping. The optical properties of the CuInS 2 :Na films revealed direct optical transitions which were attributed to the fundamental edge. The optical band gaps of the thin CuInS 2 :Na films decrease linearly with increasing the Na concentration. An unstable N type conductivity was firstly determined after what the layers are converted to P -type conductivity.

X-Ray, kinetic and optical properties of thin CuInS 2 films

In this paper we present the copper indium disulfide thin films production technology by spraying with further pyrolysis, and the results of the investigation of X-ray, kinetic and optical properties of manufactured films at 300 K. It was shown that the conductivity type and specific resistance values depend on chemical elements that dominate in the solution (indium or copper). The band gap value for CuInS 2 films, measured by absorption spectra analysis was within the range of 1.3–1.5 eV, depending on molar composition of components, temperature and type of substrate. It was shown that if the anisotropy and non-parabolicity of the hole dispersion law in D 12 2d crystals are left without consideration, it will lead to significant errors in determination of semiconductor material parameters with chalcopyrite structure.

Fabrication of CuInSe 2 films and solar cells by the sequential evaporation of In 2Se 3 and Cu 2Se binary compounds

Cu 2Se/In x Se( x≈1) double layers were prepared by sequentially evaporating In 2Se 3 and Cu 2Se binary compounds at room temperature on glass or Mo-coated glass substrates and CuInSe 2 films were formed by annealing them in a Se atmosphere at 550°C in the same vacuum chamber. The In x Se thickness was fixed at 1 μm and the Cu 2Se thickness was varied from 0.2 to 0.5 μm. The CuInSe 2 films were single phase and the compositions were Cu-rich when the Cu 2Se thickness was above 0.35 μm. And then, a thin CuIn 3Se 5 layer was formed on the top of the CuInSe 2 film by co-evaporating In 2Se 3 and Se at 550°C. When the thickness of CuIn 3Se 5 layer was about 150 nm, the CuInSe 2 cell showed the active area efficiency of 5.4% with V oc=286 mV, J sc=36 mA/cm 2 and FF=0.52. As the CuIn 3Se 5 thickness increased further, the efficiency decreased.

High-efficiency CIGS solar cells with modified CIGS surface

CIGS films were treated in In–S aqueous solution for high-efficiency CIGS solar cells. The In–S aqueous solution contained InCl 3 and CH 3CSNH 2 (thioacetamide). The In–S treatment modified the CIGS surface favorably for high-efficiency CIGS solar cells as evidenced by the increase in V oc, J sc and FF. The In–S treatment formed thin CuInS 2 layer on the CIGS surface which contributes to the high efficiency and stable performance of the CIGS solar cell. The best cell showed an efficiency of 17.6% ( V oc=0.649 V, J sc=36.1 mA/cm 2 and FF=75.1%) without any annealing and light soaking before I– V measurement.

Effect of CuIn 3Se 5 layer thickness on CuInSe 2 thin films and devices

CuInSe 2 thin films were prepared by a three-stage sequential co-evaporation of In–Se, Cu–Se, and In–Se elements for photovoltaic application. After growing CuInSe 2 films, the film surface was converted to an ordered vacancy compound (CuIn 3Se 5). The presence of a CuIn 3Se 5 layer on the CuInSe 2 surface was confirmed by XRD and AES. By the formation of the CuIn 3Se 5 phase on the CuInSe 2 surface, the absorption edge was shifted from 1200 Å to a shorter wavelength. On the CIS films, an In 2Se 3 buffer layer instead of the commonly known CdS layer was employed and deposited in the same evaporator without breaking the vacuum system. The ITO/ZnO/In 2Se 3/CuInSe 2 cells with a thin CuIn 3Se 5 layer at the In 2Se 3/CuInSe 2 interface yielded a solar efficiency of 8.46% with an active area of 0.2 cm 2 which is considered high efficiency regarding no Ga in the CIS absorber layer.

Growth of CuIn 3Se 5 layer on CuInSe 2 films and its effect on the photovoltaic properties of In 2Se 3/CuInSe 2 solar cells

The growth of CuIn 3Se 5 layer on bulk CuInSe 2 films has been studied for the fabrication of CuInSe 2 solar cells, using the three-stage process which involved the sequential evaporation of In–Se, Cu–Se, and In–Se elemental sources. After growing CuInSe 2 films, the film surface was converted to a defect chalcopyrite (CuIn 3Se 5) compound. The X-ray diffraction and AES depth analysis indicated the formation of the CuIn 3Se 5 phase on the CuInSe 2 surface. By the formation of the CuIn 3Se 5 phase, the absorption edge was shifted from 1200 to 1000 nm wavelength and the binding energies of Cu, In, and Se were shifted to higher energies. The current–voltage curves of In 2Se 3/CuInSe 2 cells fabricated with a thick CuIn 3Se 5 layer on a CuInSe 2 film displayed a kink effect which was possibly caused by the increase of series resistance and light absorption in the CuIn 3Se 5 layer instead of the junction region. The cells with a thin CuIn 3Se 5 layer at the In 2Se 3/CuInSe 2 interface yielded solar efficiency of 8.46% with an active area of 0.2 cm 2.

Optical transitions in thin CuIn(Te,Se)2 films near the fundamental absorption edge

Values for the direct valence to conduction band transition energies and corresponding values for the crystal–field and spin–orbit interaction energies for CuIn(Te,Se)2 (CITS) thin films have been extracted from the absorption data and related to compositional variations.

Energy transitions in CuIn(Te,Se)2 chalcopyrite films near the fundamental absorption edge

The structure of the fundamental absorption edge in thin CuIn(Te,Se)2 chalcopyrite films has been studied. Identifications are made of the energy transitions due to the splitting of the valence band by the tetragonal crystal field and the spin-orbit interaction. The concentration dependences of these transitions are determined

In-Situ Investigation of Cu-In-Se Reactions by Thin Film Calorimetry

AbstractStudies of the reaction path during annealing of Cu-In-Se thin films for solar cell absorbers have been limited up to now to ex-situ analyses of the phase composition by X-Ray Diffraction (XRD) after processing by a specific temperature-time program. As an indirect method, the application of ex-situ XRD is not sufficient for the determination of reaction temperatures and reaction times for setting up a general model of CIS-formation.We show in this paper that the use of a calorimetric method (Thin Film Calorimetry, TFC) offers the advantage of a direct (in-situ) observation of thin film reactions. Special care is taken to use film thicknesses of practical interest for industrial application (1.5 – 3 μm). In a first step we show results of binary reactions in the Cu-In, In-Se and Cu-Se systems. Their knowledge is necessary for understanding the processes involved in the ternary CIS-layers. It turned out that thin Cu-In and Cu-Se films react already at room temperature and behave as predicted by the bulk equilibrium phase diagrams during heating. In-Se thin films show prominent exothermic reactions starting with the melting of In. The first phase to be formed is generally In2Se which is then converted to more Se-rich compounds. In ternary Cu-In-Se films (Cu/In = 1.00) we observe transitions of the Cu-Se-system which can be attributed to the decomposition of CuSe2 and CuSe. Consequences for the model of improved CIS-growth by a Cu-Se flux agent are discussed.

Energy-gap variations in thin laser-deposited Cu(In, Ga) Se 2 films

Thin CuIn x Ga 1 − x Se 2 (0 ≤ x ≤ 1) (CIGS) films were produced by Nd:YAG-laser deposition onto glass substrates. The absorption coefficients and fundamental transition energies of highly oriented CIGS thin films were determined using interferential reflectivity and transmission in the range 400–1700 nm. The energy gaps observed in thin laser-deposited CIGS films near and above the fundamental absorption edge exhibit a nonlinear composition dependence.

Thin CuInS 2 films by three-source molecular beam deposition

We report the growth of thin CuInS 2 films by the evaporation of the elements on (100)Si and glass substrates. For the metals commercially available Knudsen effusion cells were used, while for the sulphur a new three-stage cracker cell has been developed. The polycrystalline films are characterized by Rutherford backscattering spectroscopy, X-ray diffraction, and scanning tunnelling microscopy. The effects of substrate and annealing temperatures and deposition rates on composition, crystalline order, grain size and surface morphology are investigated. The conditions for the growth of stoichiometric and planar CuInS 2 thin films of good crystal quality are determined.

Etude des propriétés optiques des couches minces de CuInS2 et d'In-S " Airless spray "

In this work we have studied the optical properties of the thin CuInS 2 and In-S layers prepared by airless spray P.S.A.. The study of the optical properties from the ellipsometric measure realized in the interval energy of incident photons [1.5-4] eV, has showed that the refraction index n, and the extinction coefficient k l vary in the interval [1.8-2.3] and [0.45-0.80] respectively. The absorption coefficient a of the thin CuInS 2 layers realized for different ratios x of the concentrations in the spray solution (x=[CuI]/[InIII]) is high with values varied between (5×10 4 and 18×10 4 cm -1 ). The direct gap energy of the thin CuInS 2 layers of the order of 1.38 eV. In the same way, we study the spectrum variation of n l (λ) and k l (λ) of the thin In-S layers, realized for two values of ratio y of the concentration in the spray solution (y=[In 3+ ]/[S -2 ]) shows that for the value of y=0.6 (material β-In 2 S 3 ) the refraction index is higher than that of teh thin layer obtained for the value of y=0.75 (material In 6 S 7 ) [1], and that the extinction coefficient is lower than that of In 6 S 7 . For In-S thin layers, α is also high with values varing between 2×10 4 and 12×10 4 cm -1 . The direct band gap of materials β-In 6 S 7 and In 6 S 7 are 2.22 eV and 1.94 eV respectively. The heat treatment under vacuum at 573 K during two hours improves the optical quality of the thin p type CuInS 2 layers

Caractérisations structurale et morphologique des couches minces de CuInS2 et d'In-S "airless spray"

We have prepared CuInS 2 thin layers by airless spray S.P.A. in order to use them as an absorber in a photovoltaic cell. The X-ray diffraction analysis has showed that these layers are well crystallized with a privileged (112) principal orientation for a ratio of the concentrations in the pulverized solution x=[Cu I ]/[In III ]=1.1. After heat treatment under vacuum the crystallization have been clearly improved. The structural analysis of the thin CuInS 2 layers have revealed that secondary phases of In 2 S 3 and In 6 S 7 are present. Thus we have realized by the same technique thin In-S layers whose structural and morphological properties have been studied. This analysis has showed that the In-S layers are well crystallized for a ratio y=[In 3+ ]/[S 2- ]=0.6 in the spray solution. The In-S layers are essentially formed by a β-In 2 S 3 material, although the In 6 S 7 phase appears to the detriment of β-In 2 S 3 phase for y=0.75

Development of CuInS 2 solar cell material by PAC: bulk phases, thin films, and nuclear reaction doping

Perturbed angular correlations (PAC) of γ-rays using 111In nuclear probes are utilized for the material development of CuInS 2. Three applications are presented which are a suitable tool to contribute to this complex: i) Using metallic In containing 111In as one of the starting materials, single- and multiphase bulk samples were grown from the melt and studied by PAC, which leads to a complete data set of PAC signatures for all In-containing phases of the Cu-In-S system that are stable at room temperature, as well as to the phase relations of CuInS 2. ii) The preparation of thin films containing 111In is controlled by PAC observing the phase formation. In first experiments, a thin Cu-In film was sulphurized, and the evaporation of sulphur out of the InS compound was studied, iii) The method of nuclear reaction doping offers the possibility to incorporate 111In afterwards in CuInS 2 thin films and bulk samples earlier produced for other purposes.

Preparation of thin CuInS 2 films via a two-stage process

Thin CuInS 2 films were made via a two-stage process. In the first step CuIn films are prepared by molecular beam deposition which are converted into CuInS 2 films in the second step by a subsequent anneal in a sulphur-containing atmosphere. In this way polycrystalline CuInS 2 films are obtained which show only the zinc blende phase. The optimum conditions for single-phase CuInS 2 formation and the influence of deviations from the ideal composition are discussed.