Spray Ion Layer Gas Reaction Research Articles

Preparation of Titania on Stainless Steel by the Spray-ILGAR Technique as Active Photocatalyst under UV Light Irradiation for the Decomposition of Acetaldehyde

One of the methods used to produce buffer layers for thin film solar cells is the Spray ion layer gas reaction (SPRAY-ILGAR). This method has exhibited astonishing efficiencies in the fabrication of homogenous compact metal chalcogenide films. The same approach can be applied in the preparation of photocatalyst on a substrate, in order to acquire a homogeneous and durable layer. In this work, the Spray-ILGAR technique has been utilized in the preparation of titania photocatalysts on stainless steel, which was carried out at Helmholtz-Zentrum Berlin for Materials and Energy, in Berlin, Germany. The characterizations and photocatalytic testing of the synthesized materials were then done at the Institute of Catalysis, Hokkaido University. The scanning electron microscopy (SEM) analysis showed that the titania was dispersed uniformly on top of the stainless steel, with a very durable and strong attachment. It was also found that the concentration of the titania on stainless steel can be easily varied by changing the concentration of the titania-precursor solution. Higher concentrations will result in a more compact and dense layer, while lowering the concentration of the precursor solution produces a less dense layer of TiO2. Apart from that, different temperatures did not change the distribution of the samples much. The photocatalytic activity of the synthesized materials was determined in terms of the photocatalytic decomposition of acetaldehyde under ultra violet (UV) light irradiation. The photocatalytic testing results proved that the samples can completely degrade acetaldehyde under UV irradiation. The heating temperature played a crucial role, as the sample prepared by with heating temperature of 550 °C, concentration of titania-precursor of 6.83 mM and a spraying time of 12 min showed the best results, requiring only 35 min to fully degrade 500 ppm of acetaldehyde.

Stoichiometry and local bond configuration of In2S3:Cl thin films by Rutherford backscattering spectrometry

In2S3 thin films deposited using chemical methods always contain residual elements from the precursors, which modify their properties. As buffer layers in solar cells, the residual elements in the In2S3 layer affect the performance of these devices. The stoichiometry of In2S3 thin films deposited by spray ion layer gas reaction (ILGAR) was studied as a function of the residual Cl from InCl3 precursor by varying the deposition parameters. The chemical formula was deduced from the elemental composition determined using Rutherford backscattering (RBS). Incomplete sulfurization of the precursor implies that residual Cl− remains bonded to the In3+ ions while some occupy interstitial and/or antisite positions in the In2S3 matrix. This results in thin films with different stoichiometry, described by the formula In4S6−xCl2x+2y. This changes the local bond configuration and geometry and underpins the influence of residual Cl on the physical properties of In2S3 thin films.

Formation of inorganic nanocomposites by filling TiO2 nanopores with indium and antimony sulfide precursor aerosols

Nanocomposites of nanoporous-TiO2/In2S3 and np-TiO2/Sb2S3 were formed by deposition of In2S3 or Sb2S3 using spray ion layer gas reaction technique from their precursor solutions onto nanoporous TiO2 substrates at temperatures of 150, 175 and 200°C. The least penetration of the precursor into np-TiO2 was achieved for np-TiO2/In2S3 nanocomposites from indium acetylacetonate salt. The deepest penetration was obtained for both np-TiO2/In2S3(Cl) and np-TiO2/Sb2S3 nanocomposites with effective diffusion coefficients of 3.3×10−3cm2/s and 3.2×10−3cm2/s, respectively. The transport of the precursors in np-TiO2 and the formation of different nanocomposites were described the regime of the Knudsen diffusion model.

Substitution of the CdS buffer layer in CIGS thin‐film solar cells

AbstractThis contribution provides an overview of current activities in the area of alternative buffer layers for Cu(In,Ga)(S,Se)2 (CIGS) thin‐film solar cells. Good cell and module results were achieved by replacing the standard Cds buffer with Zn(O,S), In2S3, (Zn,Sn)Oy or (Zn,Mg)O grown by various methods like chemical bath deposition (CBD), thermal evaporation, sputtering, atomic layer deposition, and spray ion layer gas reaction. The “dry” deposition methods like sputtering and thermal evaporation could be favorable in an industrial environment on glass substrates or application in a roll‐to‐roll coater. Significant progress was made within the last two years for various Cd‐free CIGS devices. We list current records for cells with alternative buffers, e. g. Zn(O,S)‐buffered champion cells with efficiencies between 18—20 % and In2S3‐buffered cells with 16—17 %. Both materials have the potential to substitute CdS with efficiencies approaching the 20 % mark already surpassed by CIGS cells with CBD CdS buffers.

Self-Assembled, Stabilizer-Free ZnS Nanodot Films Using Spray-Based Approaches

A direct self-assembly of high-quality, uncoated ZnS nanodots on a given substrate was obtained using two techniques: the sequential and cyclic spray ion layer gas reaction (spray-ILGAR) as well as the simultaneous and continuous spray chemical vapor deposition (spray-CVD). The spray-ILGAR nanodots are homogeneous in size (3–6 nm), regular in shape, and uniform in composition, while the spray-CVD nanodots are larger and irregular in shape with inclusions of ZnO. By employing these two spray-based techniques, the synthesis of nanodots directly assembled on the substrate surface can be realized in a controlled manner, covering a certain range of compositions, tunable sizes, and controllable interparticle distances. In situ mass spectrometry was implemented in the real-time process in order to achieve better understanding of the intrinsic chemistry involved. We systematically study the influence of the process parameters on the formation of the nanodots and compare the morphology, composition, and property of the obtained nanodots. Based on these investigations, the underlying mechanism that controls the special growth of the nanodots in spray-ILGAR and spray-CVD processes is proposed. It can account for the similarities and differences of these two kinds of nanodots. A passivation/point contact bilayer, composed of the spray-based ZnS nanodots covered by a homogeneous ILGAR In2S3 layer, is used as the buffer in the chalcopyrite solar cells, resulting in the cell performance improvement compared to the pure ILGAR In2S3 buffer.

Deposition of very thin uniform indium sulfide layers over metallic nano-rods by the Spray-Ion Layer Gas Reaction method

Very thin and uniform layers of indium sulfide were deposited on nickel nano-rods using the sequential and cyclical Spray-ILGAR® (Ion Layer Gas Reaction) technique. Substrates were fabricated by electrodeposition of Ni within the pores of polycarbonate membranes and subsequent chemical dissolution of the template. With respect to the depositions on flat substrates, experimental conditions were modified and optimized for the present geometry. Our results show that nano-rods up to a length of 10μm were covered uniformly along their full length and with an almost constant film growth rate, thus allowing a good control of the coating thickness; the effect of the deposition temperature was also investigated. However, for high numbers of process steps, i.e. thickness, the films became uneven and crusty, especially at higher temperature, mainly owing to the simultaneous side reaction of the metallic Ni forming nickel sulfide at the surface of the rods. However, such a problem occurs only in the case of reactive nano-rod materials, such as less noble metals. It could be strongly reduced by doubling the spray step duration and thereby sealing the metallic surface before the process step of the sulfurization. Thus, quite smooth, about 100nm thick coatings could be obtained.

Role of chlorine in In2S3 for band alignment at nanoporous-TiO2/In2S3 interfaces

Coatings of Cl-free and Cl-containing In2S3 (In2S3:Cl) layers were prepared by spray ion layer gas reaction on nanoporous TiO2 (np-TiO2). Charge separation in FTO/np-TiO2/In2S3:Cl, FTO/In2S3:Cl, FTO/np-TiO2/In2S3:acac, and FTO/In2S3:acac systems has been investigated by modulated surface photovoltage spectroscopy (SPV). The exponential defect tails below the band gap of In2S3 were reduced for In2S3:Cl. The analysis of the SPV spectra allowed to distinguish different mechanisms of charge separation and to deduce the conduction band offsets (about 0.3 eV and 0.05 eV for np-TiO2/In2S3:Cl and np-TiO2/In2S3:acac, respectively) in correlation with photoelectron measurements.

Spray-ILGAR ZnS nanodots/In2S3 as defect passivation/point contact bilayer buffer for Cu(In,Ga)(S,Se)2 solar cells

The sequential and cyclic spray ion layer gas reaction (spray-ILGAR) technique allows the deposition of metal chalcogenide films controllable from monodispersed nanodots to homogeneous compact layer. With access to this technique, a structured buffer layer for Cu(In,Ga)(S,Se)2 cells, named “defect passivation/point contact bilayer buffer” is introduced at the heterogeneous interfaces to replace the conventional toxic CdS buffeProd. Type: FTPr material and to improve the pure In2S3 buffer. Here, the spray-ILGAR ZnS nanodots serve as a passivation layer with a reduced interface recombination, while the compact spray-ILGAR In2S3 film on top and in-between the nanodots acts as point contact layer for the charge carrier transport. The optimal ZnS dot density and In2S3 thickness are determined and discussed in detail. As yet, the solar cell efficiency with ZnS/In2S3 buffer layer can be improved by about 1.5% absolutely as compared to a pure In2S3 buffered cell. Apart from the electronic properties of the absorber/buffer interface, also the chemical and diffusion processes during junction formation, which may influence the properties of the completed solar cell, are investigated and discussed.

Surface photovoltage spectroscopy on Cu(In,Ga)(S,Se)2/ZnS‐nanodot/In2S3 systems

ABSTRACTSingle layers and combined layer systems with Cu(In,Ga)(S,Se)2, ZnS‐nanodot (nd) and In2S3 layers were investigated by surface photovoltage spectroscopy in the Kelvin‐probe arrangement and compared with the open‐circuit voltage (VOC) of solar cells. The In2S3 and ZnS‐nd layers were prepared by the spray ion layer gas reaction (ILGAR) technique from Indium chloride (InCl3), Indium acetylacetonate (In(acac)3) and Zinc acetylacetonate, respectively. The surface photovoltage signals of Cu(In,Ga)(S,Se)2 were larger for the Cu(In,Ga)(S,Se)2/ZnS‐nd/In2S3 than for the Cu(In,Ga)(S,Se)2/In2S3 layer system showing that a ZnS‐nd layer additionally passivated the Cu(In,Ga)(S,Se)2 surface. ILGAR In2S3 deposition from InCl3 precursor solution led to a modification of surface defects of ZnS‐nd and to generation of defect states below the band gap of Cu(In,Ga)(S,Se)2, which has not been observed for deposition from Indium acetylacetonate precursor. Defect generation during ILGAR In2S3 deposition with InCl3 precursor resulted in a lower VOC of Cu(In,Ga)(S,Se)2/ZnS‐nd/In2S3/ZnO : Al solar cells. Copyright © 2012 John Wiley & Sons, Ltd.

The reaction mechanism of the spray Ion Layer Gas Reaction process to deposit In 2S 3 thin films

The spray Ion Layer Gas Reaction (ILGAR) is a well-established, patented and commercial process used primarily to deposit In 2S 3 as buffer layers in thin film solar cells. In this paper we investigate the growth mechanism of the spray In 2S 3 ILGAR process by characterising the intermediate growth stages of films, following the growth mechanism with a quartz crystal microbalance and tracking the gaseous side-and-intermediate products during film growth, using a mass spectrometer. A basic growth mechanism model is then proposed based on an aerosol assisted chemical vapour deposition of an In(O x,Cl y,(OH) z) film, as the first stage process, followed by the conversion of the intermediate film using H 2S gas to In 2S 3.

The spray-ILGAR ® (ion layer gas reaction) method for the deposition of thin semiconductor layers: Process and applications for thin film solar cells

The spray Ion Layer Gas Reaction (ILGAR) process starts with ultrasonic nebulisation of the precursor solution, e.g. InCl 3/ethanol for our successful buffer material In 2S 3. In an aerosol assisted chemical vapour deposition (AACVD) type reaction an In(O,OH,Cl) film is deposited on a heated substrate and is subsequently converted to In 2S 3 by H 2S gas. The cycle of these steps is repeated until the required layer thickness is obtained. The robust and reproducible process allows a wide control of composition and morphology. Results of this “spray-ILGAR” method with respect to process, material properties and its application depositing the buffer layer in chalcopyrite solar cells are reviewed. New aspects such as the investigation of the complex chemical mechanism by mass spectrometry, the process acceleration by the addition of H 2S gas to the aerosol, the controlled deposition of ZnS nano-dot films and finally the latest achievements in process up-scaling are also included. Solar cells based on industrial Cu(In,Ga)(S,Se) 2 absorbers (Avancis GmbH) with a Spray-ILGAR In 2S 3 buffer reached 14.7% efficiency (certified) and 15.3% with a ZnS/In 2S 3 bi-layer buffer comparable to reference cells using standard CdS buffer layers deposited by chemical bath deposition (CBD). The quasi-dry, vacuum-free ILGAR method for In 2S 3 buffer layers is well suited for industrial in-line production and is capable of not only replacing the standard buffer material (the toxic CdS) but also the often slow CBD process. A tape coater for 10 cm wide steel tape was constructed. It was shown that In 2S 3 layers could be produced with an indium yield better than 30% and a linear production speed of 1m/min. A roll-to-roll pilot production line for electrochemically deposited Cu(In,Ga)Se 2 with ILGAR buffer is running in industry (CIS-Solartechnik, Hamburg). A 30x30 cm 2 prototype of an ILGAR in-line coater developed by Singulus and Helmholtz Zentrum Berlin is currently being optimised. First 30×30 cm 2 encapsulated modules achieved efficiencies up to 13.0% (CdS buffered reference 13.3%).

Formation of CuInS2–carbon multilayers in the spray ILGAR process

AbstractIn this paper, the incorporation of carbon into CuInS2 (CIS) thin films is described as observed in spray ion layer gas reaction (ILGAR) deposition of such thin films. It is shown that this carbon incorporation leads to the formation of a CIS–carbon multilayer stack. Its growth mechanism is explained by the interaction of the copper and indium precursor compounds used in the deposition process.

Spatially resolved characterization of chemical species and crystal structures in CuInS2 and CuGax Sey thin films using Raman microscopy

AbstractThis study demonstrates the potential of Raman microscopy in the analysis of thin film cross‐sections. Raman maps of the photovoltaic material CuInS2 (CIS), which was prepared by the spray ion layer gas reaction method, revealed the spatial distribution of two different CIS modifications – chalcopyrite‐type and CuAu I‐type CIS – as well as contaminants and segregates with a lateral resolution of approx. 400 nm. Additionally, the chemical heterogeneity of a CuGaSe2/CuGa3Se5 bi‐layer stack was clearly resolved. Raman microscopy provides a convenient way to simultaneously probe the chemical and structural properties of a sample. Based on Raman spectra, chemical species and even different crystal structures of inorganic compounds can be identified. Knowledge of the distribution of different phases and contaminants in thin films is crucial for further improvements of the coating process. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO-nanorod arrays for solar cells with extremely thin sulfidic absorber

Solar cells with an extremely thin sulfidic absorber have been prepared by spray ion layer gas reaction (ILGAR) of In 2S 3 on ZnO-nanorod arrays. As transparent hole conductor, CuSCN was deposited on the coated ZnO nanorods by impregnation. Surface photovoltage spectroscopy was applied to characterize states contributing to excess carrier generation and charge separation. The charge-selective contact is formed at the In 2S 3/CuSCN interface region the states of which also contribute significantly to the photocurrent. The influence of annealing temperature and annealing time of the In 2S 3/CuSCN contact region on the open-circuit potential ( V OC), short-circuit current ( I SC) and fill factor (FF) was studied in detail. For solar cells based on ZnO-nanorod arrays (rod length 1.5 μm), efficiency of 2.8% is obtained at AM1.5.

Properties of Spray ILGAR CuInS 2 thin films

CuInS 2 thin films were prepared by using the recently presented Spray Ion Layer Gas Reaction (Spray ILGAR). Originally designed for buffer layer deposition this process has now been significantly modified in order to deposit absorber layers for thin film solar cells with thicknesses in the micrometer range. Several post deposition treatments are applied to these films. In this report the CuInS 2 films are characterized regarding structure, bulk and surface composition. X-Ray Diffraction (XRD), X-Ray Fluorescence Spectroscopy (XRF), X-Ray Photoemission Spectroscopy (XPS), and Elastic Recoil Detection Analysis (ERDA) were employed to compare the composition of these films to reference CuInS 2 films, which were prepared by Rapid Thermal Processing (RTP). It is shown that in terms of composition and surface chemistry the ILGAR films are very similar to device grade reference samples.

Deposition of In2S3 on Cu(In,Ga)(S,Se)2 thin film solar cell absorbers by spray ion layer gas reaction: Evidence of strong interfacial diffusion

Recently, Cd-free Cu(In,Ga)(S,Se)2-based “CIGSSe” thin film solar cells with a nominal In2S3 buffer layer deposited by the spray ion layer gas reaction technique resulted in photovoltaic performances comparable to that of CdS buffered references. In the past it was argued that diffusion processes across the In2S3∕CIGSSe interface play a significant role for the device quality. Investigating the interface formation by using x-ray photoelectron spectroscopy, the authors were able to confirm a strong interfacial diffusion involving Cu and Na from the CIGSSe.

Indium sulfide buffer/CIGSSe interface engineering: Improved cell performance by the addition of zinc sulfide

Indium sulfide buffer layers deposited by the spray-ion layer gas reaction (Spray-ILGAR) technique are a viable alternative to the traditional cadmium sulfide buffer layer in thin film solar cells. In the present work we report on the results of manipulating the absorber/buffer interface between the chalcopyrite Cu(In,Ga)(S,Se) 2 absorber (CIGSSe) and the indium sulfide buffer. It is shown that the deposition of a small amount of zinc sulfide at the absorber/buffer interface can be used to increase the open circuit voltage. A small but significant increase of 20 mV (up to 580 mV), as compared to the pure indium sulfide buffered cells is possible leading to an increase in the overall efficiency.

Indium sulfide thin films deposited by the spray ion layer gas reaction technique

The Spray Ion Layer Gas Reaction (Spray-ILGAR) technique is a new variation on the ILGAR technique used to prepare chalcogenide thin films. High quality indium sulfide thin films were produced by Spray-ILGAR with an indirect bandgap of 2.2 eV and a high suitability for use as buffer layers in chalcopyrite solar cells. The process involves the cyclical spray deposition of an indium containing precursor layer followed by its conversion to sulfide using hydrogen sulfide gas. Analysis of the deposition reveals that the indium chloride based precursor is transported via the vapour phase from the spray droplets to the substrate surface.

Solar Cells prepared with Spray-ILGAR Indium Sulfide buffer layers on Cu(In,Ga)Se2 Absorbers

AbstractIndium sulfide buffer layers deposited by the Spray-Ion Layer Gas Reaction (Spray-ILGAR) technique have recently been used with Cu(In,Ga)(S,Se)2 absorbers giving cells with an efficiency equal to the cadmium sulfide references. In this paper we show the first results from cells prepared with Cu(In,Ga)Se2 absorbers (sulfur free). These cells reach an efficiency of 13.1% which remains slightly below the efficiency of the cadmium sulfide reference. However, temperature dependant current-voltage measurements reveal that the activation energy of the dominant recombination mechanism remains unchanged from the cadmium sulfide buffered cells indicating that recombination remains within the space charge region.

Spray-Ion Layer Gas Reaction (ILGAR)a Novel Low-Cost Process for the Deposition of Chalcopyrite Layers up to the Micrometer Range for Photovoltaic Applications

A novel variant of the ion layer gas reaction (ILGAR) process is described. Up to now, only layers with a maximum thickness of about 100 nm could be deposited by ILGAR in a reasonable time. Replacing of dipping by spraying on a warm substrate accelerated the application of the precursor solution (e.g., metal chloride in water) by a factor of at least 100. For multinary products, all precursors are applied either simultaneously as a mixed solution or sequentially. In intervals, the spraying is stopped and the reaction gas H 2 S is allowed to flow over the substrate. A special, yet simple setup is shown, which allows also a recycling of unconverted precursor. In about an hour time, a micrometer thick layer of mixed or stacked CuS/In 2 S 3 /(Ga 2 S 3 ) (from CuCl 2 , InCl 3 and in some cases GaCl 3 , respectively) is deposited. The latter is converted to CuInS 2 (CIS) or Cu(In,Ga)S 2 (CIGS) by annealing in H 2 S/Ar at 550 °C. The thermodynamically stable product distribution for this process is calculated. The influence of the process parameters, substrate temperature during precursor deposition, annealing temperature, CuCl 2 /InCl 3 ratio and gallium addition, is studied. The layers are used as absorbers in chalcopyrite thin film solar devices. The grain size necessary for this purpose is already sufficient (ca. 0.5-0.7 μm diameter). First solar cells based on spray-ILGAR-CIS and -CIGS have been prepared and compared. The efficiency has already reached 3.4%. An unusual layer morphology is obtained when the substrate temperature is too high (> 90 °C). In this case, the layer consists of ideal hollow spheres with a hole in them. An explanation for this phenomenon is given.