Dip coating process: Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project

The technical and economic feasibility of producing solar cell quality sheet silicon by dip-coating one surface of carbonized ceramic substrates with a thin layer of large grain polycrystalline silicon was investigated. The dip-coating methods studied were directed toward a minimum cost process with the ultimate objective of producing solar cells with a conversion efficiency of 10% or greater. The technique shows excellent promise for low cost, labor-saving, scale-up potentialities and would provide an end product of sheet silicon with a rigid and strong supportive backing. An experimental dip-coating facility was designed and constructed, several substrates were successfully dip-coated with areas as large as 25 sq cm and thicknesses of 12 micron to 250 micron. There appears to be no serious limitation on the area of a substrate that could be coated. Of the various substrate materials dip-coated, mullite appears to best satisfy the requirement of the program. An inexpensive process was developed for producing mullite in the desired geometry

Silicon-on ceramic process: Silicon sheet growth and device development for the large-area silicon sheet task of the low-cost solar array project

The technical feasibility of producing solar-cell-quality sheet silicon to meet the Department of Energy (DOE) 1986 overall price goal of $0.70/watt was investigated. With the silicon-on-ceramic (SOC) approach, a low-cost ceramic substrate is coated with large-grain polycrystalline silicon by unidirectional solidification of molten silicon. This effort was divided into several areas of investigation in order to most efficiently meet the goals of the program. These areas include: (1) dip-coating; (2) continuous coating designated SCIM-coating, and acronym for Silicon Coating by an Inverted Meniscus (SCIM); (3) material characterization; (4) cell fabrication and evaluation; and (5) theoretical analysis. Both coating approaches were successful in producing thin layers of large grain, solar-cell-quality silicon. The dip-coating approach was initially investigated and considerable effort was given to this technique. The SCIM technique was adopted because of its scale-up potential and its capability to produce more conventiently large areas of SOC

DESIGN DIP COATER FOR WET COATING TECHNOLOGY

WetCoating Technology is widely usedin industries nowadays. Dip coating is one of the techniques used in Wet Coating Technology. The device required to implement the technique is called dip coater. The conventional dip coating technique used to deposit sol-gel thin films on flat substrates is well established and accepted because of its simplicity and the high coating quality that can be obtained. Advanced Material Research Centre (AMREC) SIRIM Berhad as a collaborator provided the dip coater for the project. With the current dip coater, the thin=film produced has several problems including wavy surfaces and non-uniformity of the thickness. The dip coater control box is only limited to two speed controls which are 0.5 mm/s and 1.5 mm/s. The purpose of this project is to improve the performance ofAMREC dip coater by designing a new improved dip coater. Preliminary work of the project involved evaluatingthe performance of current dip coater by analyzing the coatings produced using several characterization tools. Examination of how dip coating process works lead to the identification of what causes thepoorquality of the coating. Factors that contributed to the problems are vibration produced by the sample movement and type of the motor choosen for the dip coater. It was found that the vibration of the system can be reduced when the nut follower pitch was reduced. Circuit of the system has been redesigned to allow the change of the motor movement, control the speed and providing various speed for dipping process

Electrochemical characterization of YSZ thick films deposited by dip-coating process

Yttria stabilized zirconia (YSZ, 8% Y2O3) thick films were coated on dense alumina substrates by a dip-coating process. The suspension was obtained by addition of a polymeric matrix in a stable suspension of commercial YSZ (Tosoh) powders dispersed in an azeotropic mixture MEK–EtOH. The suspension composition was improved by the addition of YSZ Tosoh particles encapsulated by zirconium alkoxide sol containing yttrium nitrate which are the precursors of the 8-YSZ oxide. This optimal formulation allowed preparing, via a dip-coating process, thick films which were, after thermal treatment, homogeneous, dense and crack-free. A specific method was performed to measure the electrical conductivity, i.e. to determine the ionic conductivity of the film: it uses the four-point probe technique combined with ac impedance spectroscopy. The good agreement between the classical two-electrode measurements performed on YSZ pellets and the four-electrode ones performed on YSZ films allows concluding that this method is relevant for characterizing the transport properties of thick films

Functionalized Carboxylate Deposition of Triphenylamine-based Organic Dyes for Efficient Dye-sensitized Solar Cells

he standard dip-coating dye-loading technique for dye-sensitized solar cells (DSSCs) remains essentially unchanged since modern DSSCs were introduced in 1991. This technique constitutes up to 80% of the DSSC fabrication time. Dip-coating of DSSC dyes not only costs time, but also generates a large amount of dye waste, necessitates use of organic solvents, requires sensitization under dark conditions, and often results in inefficient sensitization. Functionalized Carboxylate Deposition (FCD) was introduced as an alternative dye deposition technique, requiring only 2% of the fabrication time, eliminating the need for solvents, and significantly reducing dye waste. In this study, FCD was used to deposit two relatively large triphenylamine-based organic dyes (L1 and L2). These dyes were sublimated and deposited in \u3c20 minutes via a customized FCD instrument using a vacuum of ∼0.1 mTorr and temperatures ≤280 °C. FCD-based DSSCs showed better efficiency (i.e., 5.03% and 5.46% for L1 and L2 dyes, respectively) compared to dip-coating (i.e., 4.36% and 5.35% for L1 and L2, respectively) in a fraction of the deposition time. With multiple advantages over dip-coating, FCD was shown to be a viable alternative for future ultra-low cost DSSC production

The Array Automated Assembly Task for the Low Cost Solar Array Project, Phase 2

During the program a process sequence was proposed and tested for the fabrication of dendritic welb silicon into solar modules. This sequence was analyzed as to yield and cost and these data suggest that the price goals of 1986 are attainable. Specifically, it was shown that a low cost POCL3 is a suitable replacement for the semiconductor grade, and that a suitable CVD oxide can be deposited from a silane/air mixture using a Silox reactor. A dip coating method was developed for depositing an antireflection coating from a metalorganic precursor. Application of photoresist to define contact grids was made cost effective through use of a dip coating technique. Electroplating of both Ag and Cu was shown feasible and cost effective for producing the conductive metal grids on the solar cells. Laser scribing was used to separate the cells from the dendrites without degradation. Ultrasonic welding methods were shown to be feasible for interconnecting the cells. A study of suitable low cost materials for encapsulation suggest that soda lime glass and phenolic filled board are preferred

AlPO4-C Composite Coating on Ni-based Super Alloy Substrates for High Emissivity Applications : Experimentation on Dip Coating and Spray Coating

High emissivity coating was developed on Ni-based super alloy substrates by dip coating and spray coating technique using a chemical precursor sol. The coating material was characterised thoroughly by XRD, SEM, TEM and XPS analyses. Characterisation results showed the presence of nano carbon in the AlPO4 matrix which imparted high emissivity to the coating. Emissivity of the coating varied from 0.6 to 0.9 in the wave length range : 2 µm - 25 µm depending on the thickness of the multilayered coating. Spray coating was very effective for coating the bigger substrates and TPS panels. Emissivity offered by the spray coated substrates was little lower compared to the dip coated substrates. Emissivity offered by the spray coated substrates was little lower compared to the dip coated substrates. Cyclic oxidation performances of the coated substrates at 800 °C and 1000 °C for 100 hrs of thermal exposure were recorded and compared with that of the bare substrate. The emissivity coating was found to offer substantial oxidation resistance to the base substrate at high temperatures

Immobilized photocatalyst on stainless steel woven meshes assuring efficient light distribution in a solar reactor

An immobilized TiO₂ photocatalyst with a high specific surface area was prepared on stainless steel woven meshes in order to be used packed in layers for water purification. Immobilization of such a complex shape needs a special coating technique. For this purpose, dip coating and electrophoretic deposition (EPD) techniques were used. The EPD technique gave the TiO₂ coating films a better homogeneity and adhesion, fewer cracks, and a higher ^·OH formation than the dip coating technique. The woven mesh structure packed in layers guaranteed an efficient light-penetration in water treatment reactor. A simple equation model was used to describe the distribution of light through the mesh layers in the presence of absorbing medium (e.g., colored water with humic acids). Maximum three or four coated meshes were enough to harvest the solar UV light from 300 nm to 400 nm with a high penetration efficiency. The separation distance between the mesh layers played an important role in the efficiency of solar light penetration through the coated mesh layers, especially in case of colored water contaminated with high concentrations of humic acid

Fast assembly of bio-inspired nanocomposite films

This paper presents a spin-coating layer-by-layer assembly process to prepare multilayered polyelectrolyte-clay nanocomposites. This method allows for the fast production of films with controlled layered structure. The preparation of a 100-bilayer film with a thickness of about 330 nm needs less than 1 h, which is 20 times faster than conventional dip-coating processes maintaining the same hardness and modulus values. For validation of this technique, nanocomposite films with thicknesses up to 0.5 μm have been created with the common dip self-assembly and with the spin coating layer-by-layer assembly technique from a poly(diallyldimethylammonium)chloride (PDDA) solution and a suspension of a smectite clay mineral (Laponite). Geometrical characteristics (thickness, roughness, and texture) as well as mechanical characteristics (hardness and modulus) of the clay-polyelectrolyte films have been studied. The spin-coated nanocomposite films exhibit clearly improved mechanical properties (hardness 0.4 GPa, elastic modulus 7 GPa) compared to the "pure” polymer film, namely a sixfold increase in hardness and a 17-fold increase in Young's modulu

The sol–gel route: A versatile process for up-scaling the fabrication of gas-tight thin electrolyte layers

Sol–gel routes are often investigated and adapted to prepare, by suitable chemical modifications, submicronic powders and derived materials with controlled morphology, which cannot be obtained by conventional solid state chemistry paths. Wet chemistry methods provide attractive alternative routes because mixing of species occurs at the atomic scale. In this paper, ultrafine powders were prepared by a novel synthesis method based on the sol–gel process and were dispersed into suspensions before processing. This paper presents new developments for the preparation of functional materials like yttria-stabilized-zirconia (YSZ, 8% Y2O3) used as electrolyte for solid oxide fuel cells. YSZ thick films were coated onto porous Ni-YSZ substrates using a suspension with an optimized formulation deposited by either a dip-coating or a spin-coating process. The suspension composition is based on YSZ particles encapsulated by a zirconium alkoxide which was added with an alkoxide derived colloidal sol. The in situ growth of these colloids increases significantly the layer density after an appropriated heat treatment. The derived films were continuous, homogeneous and around 20 μm thick. The possible up-scaling of this process has been also considered and the suitable processing parameters were defined in order to obtain, at an industrial scale, homogeneous, crack-free, thick and adherent films after heat treatment at 1400 °C