Plain Stainless Steel Research Articles

Cyclic Strain Accumulation of Plain Stainless Steel Pressurized Cylinders Subjected to Dynamic Bending Moment

Cyclic Strain Accumulation of Plain Stainless Steel Pressurized Cylinders Subjected to Dynamic Bending Moment

Thin film nanocrystalline silicon and nanostructured interfaces for multibandgap triple junction solar cells

AbstractWe present the main research aspects encountered during the development of thin film silicon‐based single and multijunction solar cells using hot‐wire chemical vapor deposition (HWCVD) of the active silicon layers. First of all, a significant current enhancement is obtained by using textured Ag/ZnO back contacts instead of plain stainless steel. The textured interface acts as a diffuse scattering mirror, due to which the optical path in the cell is lengthened. We studied the root‐mean‐square (RMS) roughness by 2D atomic force microscopy (AFM) and found that the morphology of the surfaces needs to be controlled to avoid cavities and shunting paths. A further drawback of such rough metallic surfaces is the parasitic absorption due to surface particle plasmons. Nevertheless, optimized back reflectors lead to an enhancement of the photocurrent of as much as 50%. The second large step forward is the use of multijunction (tandem) cells, in which at least one of the cells contains nanocrystalline silicon. This material behaves optically like 1.1 eV material and, used in the bottom cell, it forms a perfect combination with the 1.7 eV amorphous material in the top cell. Using silicon germanium (1.5 eV) in the middle cell, our triple junction cells have reached nearly 11% efficiency and they are stable within 3% relative. The difference between the best single junction and triple junction n‐i‐p cells obtained so far in our lab and the reported best cells with plasma‐enhanced chemical vapor deposition (PECVD) i‐layers can be mainly attributed to the differences in the rough substrates and to the use of rather thin i‐layers. Copyright © 2008 John Wiley & Sons, Ltd.

Nanostructured thin films for multiband-gap silicon triple junction solar cells

By implementing nanostructure in multiband-gap proto-Si/proto-SiGe/nc-Si:H triple junction n–i–p solar cells, a considerable improvement in performance has been achieved. The unalloyed active layers in the top and bottom cell of these triple junction cells are deposited by Hot-Wire CVD. A significant current enhancement is obtained by using textured Ag/ZnO back contacts instead of plain stainless steel. We studied the correlation between the integrated current density in the long-wavelength range (650–1000 nm) with the back reflector surface roughness and clarified that the rms roughness from 2D AFM images correlates well with the long-wavelength response of the cell when weighted with a Power Spectral Density function. For single junction 2-μm thick nc-Si:H n–i–p cells we improved the J sc from 15.2 mA/cm 2 for plain stainless steel to 23.4 mA/cm 2 using rough back reflector. We introduced profiling of the H 2 dilution during growth of the nc-Si:H layer to prevent a transition to amorphous growth. The efficiency for a single junction n–i–p cell reached 8.5%, the highest reported value for HWCVD cells of this kind. Moreover, these cells show to be totally stable under light-soaking tests. Combining the above techniques, an efficiency of 10.9% has been obtained for triple junction cells ( J sc = 8.35 mA/cm 2, V oc = 1.98 V, FF = 0.661). By using effective light trapping techniques and three different band-gap materials, the required thickness could be kept small (∼ 2.5 μm total).

Identification and control of metal transfer in pulsed GMAW using optical sensor

The aim of the present work was to design and develop an identification device for droplet detachments during pulsed GMAW and to assess the possibility of implementing a metal transfer control system. The developed identification device was based on a luminescence sensor and an electronic interface, capable of sensing the arc light flux. A basic control system for the pulse parameters was implemented using an A/D–D/A board for receiving signals from the sensor and sending instructions to an electronic power source and a trained neural network for the metal transfer recognition. Alternatively, the signal from the electronic interface could be directed to a microcomputer with a dedicated monitoring program. Automated pulsed welding was carried out on plain carbon steel, aluminium and stainless steel plates in the flat position. The metal transfers were recorded using a high speed camera and applying the shadowgraphy technique to validate the device performance. The results showed that the detachment device was efficient and consistent for aluminium (best results), stainless steel and low carbon welding. Moreover, the control system was capable of setting parameters that provided stable transfer at one drop per pulse rate, from welds starting at inadequate pulse parameter levels.

Triple Junction n-i-p Solar Cells with Hot-Wire Deposited Protocrystalline and Microcrystalline Silicon

AbstractWe have implemented a number of methods to improve the performance of proto-Si/proto-SiGe/μc-Si:H triple junction n-i-p solar cells in which the top and bottom cell i-layers are deposited by Hot-Wire CVD. Firstly, a significant current enhancement is obtained by using textured Ag/ZnO back contacts developed in house instead of plain stainless steel. We studied the correlation between the integrated current density in the long wavelength range (650-1000 nm) with the back reflector surface roughness and clarified that the rms roughness from 2D AFM images correlates well with the long wavelength response of the cell when weighted with a Power Spectral Density function. For single junction 2-μm thick μc-Si:H n-i-p cells we improved the short circuit current density from the value of 15.2 mA/cm2 for plain stainless steel to 23.4 mA/cm2 for stainless steel coated with a textured Ag/ZnO back reflector.Secondly, we optimized the μc-Si:H n-type doped layer on this rough back reflector, the n/i interface, and in addition used a profiling scheme for the H2/SiH4 ratio during i-layer deposition. The H2 dilution during growth was stepwise increased in order to prevent a transition to amorphous growth. The efficiency that was reached for a single junction μc-Si:H n-i-p cell was 8.5%, which is the highest reported value for hot-wire deposited cells of this kind, whereas the deposition rate of 2.1 Å/s is about twice as high as in record cells of this type so far. Moreover, these cells show to be totally stable under light-soaking tests.Combining the above techniques, a rather thin triple junction cell (total silicon thickness 2.5 μm) has been obtained with an efficiency of 10.9%. Preliminary light-soaking tests show that this type of triple cells degrades by less than 4%.

Boiling Heat Transfer on Wire-Mesh-Wrapped Extended Tube Surfaces

This article discusses one of the most promising techniques for enhancing boiling heat transfer by wrapping a wire mesh around a plane surface. Experimental investigations have been carried out to study boiling heat transfer for a plain stainless steel tube and stainless steel tubes wrapped with different sizes of stainless steel wire mesh, for saturated distilled water at atmospheric pressure in cross-flow configurations. The mass flux was varied from 0 to 8.27 kg/(m2 s), and the tubes were heated resistively with a heat flux ranging from 12 to 55 kW/m2. The results show that the tubes wrapped with wire mesh provide better performance than the plain tube at low heat flux (up to 30 kW/m2), whereas at high heat flux, the order of their performance reverses. The increase in boiling heat transfer is due to the enhanced retention time of the bubbles over tube surface and the increase in turbulence created around the tube surface as a result of the wire-mesh wrapping. The effects of input parameters such as the heat flux and mass flux on the boiling heat transfer coefficient for plain and wire-mesh-wrapped tube surfaces were also investigated in the present work.

Hot-wire chemical vapor-deposited microcrystalline silicon in single and tandem n–i–p solar cells

This paper examines the potential of μc-Si deposited by hot-wire chemical vapor deposition (HWCVD) at a constant hydrogen dilution of 0.95, as absorber layer in n–i–p thin film solar cells. For a series of single junction cells onto plain stainless steel, the highest open circuit voltage (Voc) and Fill Factor (FF) were 0.54V and 0.72. From J–V measurements at reduced light intensities, the change of the AM1.5-normalized FF values with light intensity was found to depend on the μc-Si i-layer thickness. This is attributed to the thickness evolution of the i-layer crystallinity, which influences the cell properties, particularly for i-layers thinner than 2.0μm. For thicker layers the measurements clearly show drift-driven charge carrier collection. Tandem cells showed FF values as high as 0.77, which indicates the very high optoelectronic quality of the μc-Si material. A 2.0μm cell on a textured back reflector shows an efficiency of 7.8%.

High Quality Hot-wire Microcrystalline Silicon for Efficient Single and Multijunction N-i-p Solar Cells

AbstractIn this paper, the potential of hot-wire chemical vapor-deposited (HWCVD) microcrystalline silicon (μc-Si) for use in solar cells is explored. Incorporation of the material in the current-limiting bottom cell of two tandem cells on plain stainless steel resulted in FF values as high as 0.77, which is much higher than the highest single junction FF. A combination of experiments, calculations and computer simulations was employed to identify causes for the observed high tandem cell FF values. Both the light intensity and the spectral composition of the bottom cell illumination in a tandem were found to contribute to an increase of the bottom cell FF. The fact that the operational voltage of a tandem cell is higher than that of the current-limiting subcell, was calculated to lead to a tandem FF that can be far higher than that of the limiting cell. Com-puter simulations with the AMPS computer code show that the current mismatch in a tandem cell reduces the recombination in the current-limiting cell, possibly by slightly enhancing the internal field of that cell. Use of a 1.5 μm ìc-Si:H hot-wire deposited absorber layer in a single junction cell on a textured back reflector yielded a Voc, FF and Jsc of 0.543 V, 0.656 and 23.60 mA/cm2, respectively, which combine to an 8.4 % record efficiency for μc-Si single junction n-i-p cells with a hot-wire intrinsic layer.

The erosion–corrosion behaviour of high velocity oxy-fuel (HVOF) thermally sprayed inconel-625 coatings on different metallic surfaces

The minimization of cost and the enhancement of reliability of rotating and stationary fluid machinery equipment that are subjected to highly erosive and corrosive environments is mandatory in the oil and gas production industries. This can be achieved by minimizing the material damage resulting from the combination of solid particle impingement and corrosion. The high velocity oxy-fuel (HVOF) process is one method of producing metallic coatings to protect metallic surfaces from high temperature, wear, and corrosive environments. Stainless steel components coated with Inconel-625 are very common in the oil/gas industry. In this study, the erosion–corrosion characteristics of HVOF thermally sprayed Inconel-625 powder coatings were evaluated when applied on three different metallic surfaces: (a) plain stainless steel (SS), (b) spot-welded stainless steel (SW-SS), and (c) a composite surface of stainless steel and carbon steel welded together (C-SS-CS). These coated surfaces were tested in a jet impingement rig under two fluid conditions: (i) free from added solids, (ii) containing 1% silica sand. Weight loss measurements were used to provide a measure of the amount of material loss that each coated surface experienced, and the influence of time during impingement testing was taken into consideration. The surface morphology and the elemental composition of the coating before and after the erosion–corrosion test were examined using the SEM and EDS techniques. The results indicated that the coating over both spot-welded and plain stainless steel surfaces exhibited a similar degree of weight loss. However, the coating on the composite surface experienced a greater degree of weight loss. Microscopic observations of the fracture surfaces showed that the metal removal of the tested surface was concentrated around the unmelted and the semi-melted particles of the deposit.

Tandem and triple junction silicon thin film solar cells with intrinsic layers prepared by hot-wire CVD

Hot-wire CVD (HWCVD) can be applied for the deposition of various types of silicon films. At Utrecht University intrinsic layers of high optoelectronic quality have been successfully used as the absorber layers in thin film solar cells. This paper presents results for a proto-Si/μc-Si cell and a proto-Si/μc-Si/μc-Si triple junction cell with its μc–μc middle-bottom tandem cell, all deposited in nip configuration onto plain stainless steel. The proto-Si/μc-Si tandem had a good V oc of 1.38 V and a high FF of 0.75. Its efficiency of 7.3% was, considering the absence of a back reflector, adequate. The μc–μc tandem cell had a good V oc of 1.04 V and a very high FF of 0.77. Since both tandem cells were current-limited by the bottom cell, the high FF-values indicate that our μc-Si material is of very high quality. The triple cell had a lower FF of 0.69 and its V oc of 1.77 V was lower than the sum of the middle–bottom tandem and the top cell. Filtered light-IV measurements on the μc–μc tandem cell indicated that the losses in FF and V oc observed for the triple cell are, at least partly, a result of the optical absorption by the proto-Si top cell.

Preparation of microcrystalline silicon nip solar cells and amorphous–microcrystalline nipnip tandem solar cells entirely by hot-wire CVD

Recently, we reported on all-microcrystalline nip solar cells with all silicon layers prepared by hot-wire chemical vapour deposition (HWCVD), achieving initial and stable conversion efficiencies of η = 5.4% ( V oc = 485 mV, j sc = 16.5 mA cm − 2, FF = 67.9%) for an i-layer thickness of 1.5 μm on simple stainless steel substrates [M. Kupich, D. Grunsky, P. Kumar, B. Schroeder, Sol. Energy Mater. Sol. Cells 81 (2004) 141] [1]. These nip solar cells were found to be absolutely stable against light induced degradation. Furthermore, these microcrystalline nip structures were successfully incorporated for the first time into all-hot-wire amorphous–microcrystalline nipnip tandem solar cells. Initial conversion efficiencies up to η = 7.0% on plain stainless steel substrates were obtained. These tandem structures showed only small SWE-like degradation. Further improvement of the solar cell performance, especially by the use of highly reflecting substrates with improved light trapping, is part of the ongoing work. First solar cells prepared on textured etched Ag/ZnO substrates provided by the IPV Juelich [O. Kluth, O. Vetterl, R. Carius, F. Finger, S. Wieder, B. Rech, H. Wagner, Mater. Res. Soc. Symp. Proc. 557 (1999) 731] [2] show increased initial efficiencies of η = 5.6% for microcrystalline single junction nip solar cells and η = 7.9% for “micromorph” nipnip tandem solar cells, due to higher current densities achievable by the enhanced light trapping.

HVOF coating of welded surfaces: Fatigue and corrosion behaviour of stainless steel coated with Inconel-625 alloy

A variety of metallic coatings, produced via the high velocity oxygen fuel (HVOF) process, are available to protect metallic surfaces from high temperature, wear and corrosive environments. Investigation into corrosion and fatigue properties of HVOF coatings is important as they affect the parameters of coated surfaces in their practical applications. In this study, the fatigue behaviour of welded and plain stainless steel surfaces thermally coated with HVOF sprayed Inconel-625 alloy was evaluated under three conditions: (a) surface as-coated, (b) surface as-coated and subjected to aqueous static corrosion for 2 weeks and (c) surface as-coated and subjected to aqueous static corrosion for 4 weeks. The surface morphology and the elemental composition of the coating before and after the fatigue–corrosion test were examined using SEM and EDS techniques. The results indicated that the welded-coated specimen under the three different conditions exhibited a similar fatigue life compared to the plain-coated specimen. However, there was a considerable reduction in the fatigue strength of the coating when subjected to 4 weeks aqueous corrosion medium. Microscopic observations of the fracture surfaces showed that the fatigue cracks were formed at both the interface between coating and substrate, and within the coating itself.

A dataset of steam condensation over a double enhanced tube bundle under vacuum

Low pressure steam condensation on a double enhanced copper nickel tube bundle under loaded conditions. Energy balance indicates the accuracy of the dataset to within 10%. Checks on shell side measurements indicate they are of good quality. A comparison is made with the Nusselt model on plain copper tubes and with data from previous plain stainless steel tubes. Previous research on steam condensation indicates the tube side resistance is usually dominant. However, on the double enhanced tube bundle, the condensate film resistance is controlling. There is no marked improvement by the double enhanced tubes while using water as the process fluid. It is postulated that high surface tension fluids, such as water, cause fin inundation (thicker condensate film) and negates any heat transfer enhancement.

Protocrystalline Silicon at High Rate from Undiluted Silane

ABSTRACTHot Wire Chemical Vapor Deposition (HWCVD) is shown to be a fast method for the deposition of protocrystalline silicon films from undiluted silane. Intrinsic silicon-hydrogen films (2 μm thick) have been deposited by HWCVD on plain stainless steel as well as on stainless steel precoated with a n-type doped microcrystalline silicon layer. In X-ray diffraction experiments, the linewidths of the first sharp peak (FSP) were 5.59 ± 0.09 degrees and 5.29 ± 0.11 degrees, respectively, indicating improved medium-range order and a template effect due to the μc-Si:H n-layer. For thinner layers (0.7 μm thick), the linewidths of the FSP were 5.29 ± 0.09 degrees and 5.10 ± 0.09 degrees. These FSPs are as narrow as for optimized i-layers made by H2-diluted plasma deposition, however, at a much higher deposition rate (1 nm/s), at moderate temperature (250°C), and without the use of H2 dilution. In accompanying transmission electron micro-graphs, the layers show a significant concentration of elongated small voids in the growth direction that are not interconnected. Small Angle X-ray Scattering (SAXS) results are consistent with these observations. We suspect that the void nature allows the bulk of the film to be more ordered. The utilization of such layers in n-i- p solar cells on plain stainless steel leads to cells with a remarkably good stability, showing a decrease of the fill factor of less than 10 % during 1500 h of light soaking.

Present status of micro- and polycrystalline silicon solar cells made by hot-wire chemical vapor deposition

Considerable effort is presently put into the development of thin film microcrystalline silicon, because it has a larger long-wavelength response than amorphous silicon, while at the same time it is essentially stable. In this review, the latest achievements in this field as obtained by hot-wire chemical vapor deposition (HWCVD) technology are presented and illustrated by the performance of silicon thin film devices. Since microcrystalline silicon has an indirect band gap, the absorption coefficient is low. Nevertheless, using light trapping geometries, the required thickness can be kept below 2 μm. In spite of this small thickness long deposition times are still required and therefore the achievement of higher deposition rates is important for production. Alternatively, multijunction cells, including amorphous components made at a higher deposition rate, can lead to lower costs while improving the overall efficiency. By doubling the catalytic surface in HWCVD, we have recently achieved a deposition rate of 7 nm/s for polycrystalline silicon. As these layers tend to be more porous, a new optimum in the gas-phase reaction chemistry was found in a regime of reduced filament temperature and higher hydrogen dilution. This has led to polycrystalline n–i–p type cells made at more than twice the deposition rate while reproducing the cell efficiency. If the crystallinity is relaxed, allowing an increase of the amorphous volume fraction, microcrystalline silicon (rather than polycrystalline silicon) is obtained. In this mode, the layers more readily possess the compactness that is required to prevent post-oxidation. We present the world's first HWCVD multibandgap triple junction cell with an efficiency of 9.1% on plain stainless steel and show the future potential of this technology.

Silver Containing Stainless Steel as a New Outlook to Abate Bacterial Adhesion and Microbiologically Influenced Corrosion

Biofouling and microbiologically influenced corrosion (MIC) are alarming processes of material deterioration. The scenario originates from the attachment of microorganisms as quickly as a material is immersed in a non-sterile environment. Stainless steels, in spite of their wide use in different industries and as appliances and implant materials, do not possess inherent antibacterial properties. To make stainless steel antibacterial and thus to mitigate MIC and bacterial infection was the purpose of this study. AISI type 304 stainless steels containing silver as an alloying element and silver coated are tested for the antibacterial efficacy as well as MIC resistance keeping plain stainless steel as control. Experimental coupons were exposed to a dilute nutrient medium containing Pseudomonas sp., isolated from a corrosive ground water environment. Coupons were exposed for varying duration (maximum 6 days), and bacterial adhesion was monitored by using epifluorescence microscope and quantified with the help of image processing software. In another experiment, free corrosion potential of these materials was monitored for 60 days. The area of bacterial adhesion was found to be significantly lesser in case of silver containing coupons compared to control. Silver alloyed coupons showed better antibacterial effect than the silver-coated coupons. Free corrosion potential showed ennoblement in the case of control coupons, while silver alloyed and silver coated coupons showed substantially lesser fluctuation. SEM observation showed pitting corrosion by 30 days in control coupons, whilst, pits were near nil on silver alloyed and very less on silver coated coupons. The results, thus suggest that silver containing stainless steels possess antibacterial properties and are resistant to MIC as compared to 304 SS. Furthermore, a field study, where the coupons were exposed to a freshwater pond showed that coupons containing silver possessed significant resistance to microfouling build-up until a period of 30 days, suggesting the possibility of using these materials in freshwater environments where microfouling is a persistent problem. As an attempt to investigate the actual damage the silver caused in the bacterium, cell walls and intracellular changes were observed under a transmission electron microscope (TEM).

Advances in solar cells made with hot wire chemical vapor deposition (HWCVD): superior films and devices at low equipment cost

This paper reviews the history of hot wire chemical vapor deposition (HWCVD) and discusses the unique silicon thin film materials that can be obtained with this deposition method. The structure of the silicon films can be widely varied from fully amorphous to completely polycrystalline. Moreover, the hydrogen content can be controlled over a wide range. A characteristic feature of HWCVD is the high deposition rate for all types of films. A ‘HW’ solar cell toolbox is presented and the first efficient a-Si/poly-Si multibandgap tandem cells have been made using developed component cells. These cells consist of two stacked n–i–p-type solar cells on plain stainless steel using plasma deposited n- and p-type doped layers and hot wire deposited intrinsic (i) layers, where the i-layer is either amorphous (band gap 1.8 eV) or polycrystalline (band gap 1.1 eV). For the two absorber layers, we used individually optimized parameters such as gas pressure, hydrogen dilution ratio, substrate temperature, filament temperature and filament material. The solar cells do not comprise an enhanced back reflector, but feature a natural mechanism for light trapping, due to the texture of the (220) oriented poly-Si absorber layer and the fact that all subsequent layers are deposited conformally. The deposition rate for the throughput-limiting step, the poly-Si i-layer, is ≈5 Å/s. This layer also determines the highest substrate temperature required during the preparation of these tandem cells (<500 °C). The efficiency obtained for these tandem cells is 8.1%. The total thickness of the silicon nip/nip structure is only 1.1 μm.

Application of hot-wire chemical vapor-deposited Si:H films in thin film transistors and solar cells

This paper shows a wide range of applications of the hot-wire chemical vapor deposition (HWCVD) method to either deposit photosensitive hydrogenated amorphous silicon (a-Si:H), polysilicon (poly-Si) and heterogeneous Si materials, dielectric hydrogenated amorphous silicon nitride (a-SiNx:H) of device quality, or to carry out hydrogen passivation treatments. Various choices of deposition parameters, i.e. process temperature, wire temperature and filament materials, have been investigated to decide the growth rate, substrate material and device configuration. The main feature of our poly-Si films is the compact nature, which manifests itself in anti-ferromagnetically-coupled defect dimer formation and hydrogen diffusion through compact sites. Very thin grain-boundary defects, purely intrinsic nature and very low oxygen incorporation, both during and post-deposition, have resulted in poly-Si films of device quality. Thin film transistors (TFTs) and solar cells have been fabricated using the above-mentioned HWCVD-deposited materials. Highly stable TFTs in the inverted staggered configuration, using heterogeneous Si, showed a field effect mobility of 1.5 cm2 V−1 s−1, whereas top-gate TFTs using poly-Si on glass showed a mobility of 4.7 cm2 V−1 s−1. The paper demonstrates the application of HWCVD a-SiNx as a dielectric material in bottom-gate TFTs, and complete TFTs have been successfully fabricated by the HWCVD process (except the contact layers). Solar cells in an n–i–p structure on plain stainless steel (SS) substrate showed efficiencies of 7.2% for a-Si:H and 4.4% for poly-Si i-layers. An a-Si/poly–Si tandem cell, with all-HWCVD i-layers, on a SS substrate without a back reflector and texturization yielded an efficiency of 8.1%. This was achieved at a deposition rate of 10 Å s−1 for poly-Si.

Stimulation of a Conductive Liquid Jet Directly Heated by an Electric Current

This paper presents experiments performed on a conductive liquid jet stimulated by an inner volume heating. The stimulating device consists in a couple of plain stainless steel electrodes located within the channel feeding the nozzle, the liquid flowing through the electrode clearance being heated by Joule effect. By applying an appropriate electrical signal, the stimulating device significantly reduces the jet break-up length and produces a very stable stream of droplets. The break-up length varies semi-logarithmically with the applied electric power. We emphasize on printer applications by performing experiments on typical continuous ink jets of small diameter (&#x223C;50 &#x3BC;m). Finally, the physical mechanisms giving rise to the stimulation are briefly discussed.

Thin Film a-Si/poly-Si Multibandgap Tandem Solar Cells With Both Absorber Layers Deposited by Hot Wire Cvd

ABSTRACTThe first competitive a-Si/poly-Si multibandgap tandem cells have been made in which the two intrinsic absorber layers are deposited by Hot Wire Chemical Vapor Deposition (HWCVD). These cells consist of two stacked n-i-p type solar cells on a plain stainless steel substrate using plasma deposited n- and p-type doped layers and Hot-Wire deposited intrinsic (i) layers, where the i-layer is either amorphous (band gap 1.8 eV) or polycrystalline (band gap 1.1 eV). In this tandem configuration, all doped layers are microcrystalline and the two intrinsic layers are made by decomposing mixtures of silane and hydrogen at hot filaments in the vicinity of the substrate. For the two layers we used individually optimized parameters, such as gas pressure, hydrogen dilution ratio, substrate temperature, filament temperature, and filament material. The solar cells do not comprise an enhanced back reflector, but feature a natural mechanism for light trapping, due to the texture of the (220) oriented poly-Si absorber layer and the fact that all subsequent layers are deposited conformally. The deposition rate for the throughput limiting step, the poly-Si i-layer, is ≍ 5-6 Å/s. This layer also determines the highest substrate temperature required during the preparation of these tandem cells (500 °C). The initial efficiency obtained for these tandem cells is 8.1 %. The total thickness of the silicon nip/nip structure is only 1.1 µm.