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1 – 10 of 797Kazimierz Drabczyk, Jaroslaw Domaradzki, Grazyna Kulesza-Matlak, Marek Lipinski and Danuta Kaczmarek
The purpose of this paper was investigation and comparison of electrical and optical properties of crystalline silicon solar cells with ITO or TiO2 coating. The ITO, similar to TiO…
Abstract
Purpose
The purpose of this paper was investigation and comparison of electrical and optical properties of crystalline silicon solar cells with ITO or TiO2 coating. The ITO, similar to TiO2, is very well transparent in the visible part of optical radiation; however, its low resistivity (lower that 10-3 Ohm/cm) makes it possible to use simultaneously as a transparent electrode for collection of photo-generated electrical charge carriers. This might also invoke increasing the distance between screen-printed metal fingers at the front of the solar cell that would increase of the cell’s active area. Performed optical investigation showed that applied ITO thin film fulfill standard requirements according to antireflection properties when it was deposited on the surface of silicon solar cell.
Design/methodology/approach
Two sets of samples were prepared for comparison. In the first one, the ITO thin film was deposited directly on the crystalline silicon substrate with highly doped emitter region. In the second case, the TCO film was deposited on the same type of silicon substrate but with additional ultrathin SiO2 passivation. The fingers lines of 80 μm width were then screen-printed on the ITO layer with two different spaces between fingers for each set. The influence of application of the ITO electrode and the type of metal electrodes patterns on the electrical performance of the prepared solar cells was investigated through optical and electrical measurements.
Findings
The electrical parameters such as short-circuit current (Jsc), open circuit voltage (Voc), fill factor (FF) and conversion efficiency were determined on a basis of I-V characteristics. Short-circuit current density (Jsc) was equal to 32 mA/cm2 for a solar cell with a typical antireflection layer and 31.5 mA/cm2 for the cell with ITO layer, respectively. Additionally, electroluminescence of prepared cells was measured and analysed.
Originality/value
The influence of the properties of ITO electrode on the electrical performance of crystalline silicon solar cells was investigated through complex optical, electrical and electroluminescence measurements.
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Devrim Anil and Can Çoğun
The purpose of this paper is to produce electric discharge machining (EDM) electrodes by using stereolithography (SLA) rapid prototyping technique and investigate the machining…
Abstract
Purpose
The purpose of this paper is to produce electric discharge machining (EDM) electrodes by using stereolithography (SLA) rapid prototyping technique and investigate the machining performance of these electrodes. In the experimental part of the study, the performance of solid copper and copper‐coated SLA (cc/SLA) electrodes are observed and compared.
Design/methodology/approach
The performance outputs such as material removal rate, machining depth, workpiece surface roughness and electrode front surface wear are used as metrics of comparison. The temperature measurements taken from the face of both solid copper and cc/SLA electrodes indicated that the heat build up during machining significantly accelerated the failure of cc/SLA electrodes.
Findings
The paper finds that circulating the cooling liquid inside the internal cooling channels formed with SLA technique, elongated the life of cc/SLA electrodes by dissipating the heat from the coating.
Originality/value
The Fluent Computational Fluid Dynamics (CFD) Software is used to numerically analyze various aspects of cooling of cc/SLA electrodes. The key findings of the study are presented in this paper.
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Kazimierz Drabczyk, Robert P. Socha and Agata Skwarek
The aim of this paper is to present results of investigations carried out on the front electrode of solar cells. Nowadays, most worldwide solar cell production is dominated by…
Abstract
Purpose
The aim of this paper is to present results of investigations carried out on the front electrode of solar cells. Nowadays, most worldwide solar cell production is dominated by monocrystalline and polycrystalline silicon as a base material. In such cells, the electrical carriers are collected by the system of metallic paths fabricated on a silicon surface. One possible way to increase cell efficiency and reduce the production costs of solar modules is to replace the expensive silver by cheaper copper in front metallic electrodes.
Design/methodology/approach
The paper presents results of investigations performed on the front electrode of the solar cell. The investigations were focused on the modification of typical screen printing fabrication of the thin electrical finger paths of the front solar cell electrode. The resulting contacts were characterized morphologically (the dimensions and geometry of the front contacts) by scanning electron microscopy. The composition of finger path covered with copper was analyzed using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy techniques.
Findings
In this work, the front electrodes were screen printed with the use of conventional silver-paste on a p-type Cz–Si-textured wafer with a n+ emitter and with an antireflection coating. After that, the fired front electrode was electroless coated with copper. The electroless copper deposition was performed in two stages. First, the surface of the photovoltaic cell was dipped in an aqueous solution of CuSO4 and then dried in air at room temperature. When the surface dried, the cell was immersed in hydrogen fluoride solution (5 per cent) for 1 s followed by rinsing in deionization water.
Originality/value
The experiments confirmed the potential application of copper as an additional layer of the solar cell front metal electrode. On the one hand, this process is very simple and, on the other, the authors demonstrate a problem with the mechanical stability of the covered paths leading to electrode delamination.
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Kazimierz Drabczyk and Piotr Panek
The paper aims to present results of investigations carried out on the front electrode of the solar cell. The front-side electrode for solar cells based on crystalline material is…
Abstract
Purpose
The paper aims to present results of investigations carried out on the front electrode of the solar cell. The front-side electrode for solar cells based on crystalline material is obtained by the screen printing method. Screen printing has been the prevailing method of electrode deposition because of its low cost. One of the ways to improve the cell efficiency and reduce the production costs is a further refinement of the metal electrode screen printing process.
Design/methodology/approach
The researches were focused on the modification of mechanical parameters of screen printing process to ensure the best possible cross-section of the front electrode geometry. The main printing process parameters were constant, however, the print speed was variable. The obtained fine line of front contact was characterized morphologically – the dimension and geometry of the front contact cross-section – by scanning electron microscopy technique.
Findings
The thin paths of 100 μm in width were screen printed applying a new silver-paste made by Du Pont. The printing speed has significant effect on print quality in the way that the lower speed enhanced the printed results.
Research limitations/implications
For newest pastes (e.g. PV17D) influence of screen printing parameters on the front metallic electrodes geometry of solar cell is not so significant. Presented screen printing process can still give good results, but the further optimization for the new paste must be performed to achieve better cross-section geometry.
Originality/value
This paper confirms that one-step screen printing process can still give good results. The screen printed thin paths of 100 μm in width have good cross-section aspect ratio.
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Kazimierz Drabczyk, Jaroslaw Domaradzki, Piotr Panek and Danuta Kaczmarek
The purpose of this paper was the investigation of transparent conducting oxide (TCO) applied as an additional part of front metal electrode of crystalline silicon solar cell…
Abstract
Purpose
The purpose of this paper was the investigation of transparent conducting oxide (TCO) applied as an additional part of front metal electrode of crystalline silicon solar cell. Transparent conducting oxides are widely used as counter electrodes in a wide range of electronics and optoelectronics applications, e.g. flat panel displays. The most important optical and electrical requirements for TCOs are high optical transmittance and low resistivity. This low resistivity might invoke the possibility of increasing the distance between the fingers in the solar cell front electrode, thus decreasing the total area covered by metal and decreasing the shadowing loss.
Design/methodology/approach
In the present work, thin films of indium-tin-oxide (ITO) as a transparent counter electrodes, were evaporated on the surface of silicon n+-p junction structures used in solar cells. The influence of the properties of ITO electrode on the electrical performance of prepared solar cells was investigated through optical and electrical measurements. The discussion on the influence of deposition conditions of the TCO films on recombination of the photogenerated electrical charge carriers and solar cell series resistance was also included.
Findings
In this work, the fingers lines 100 μm width were screen-printed on the c-Si wafer with ITO layer. Monocrystalline silicon 25 cm 2,200-μm-thick wafers, were used for this testing. The usefulness of the ITO films as antireflection coating was discussed as well. It is commonly known that electrical performance of solar cells is limited by surface passivation. Despite this, the obtained results for ITO-Si structures showed relatively high value of short circuit current density (Jsc) up to 33 mA/cm2.
Originality/value
Our experiments confirmed the potential of application of ITO as anti-reflection coating (ARC) layer and according to their low resistivity possible use as a functional counter electrodes in photovoltaic structures.
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Eduardo José Lima and Alexandre Queiroz Bracarense
Shielded metal arc welding (SMAW) is a typical manual process with many important but dangerous applications for the welder. The purpose of this paper is to present a methodology…
Abstract
Purpose
Shielded metal arc welding (SMAW) is a typical manual process with many important but dangerous applications for the welder. The purpose of this paper is to present a methodology developed for execution time trajectory generation for robotic SMAW which offers greater safety and improved weld quality and repeatability.
Design/methodology/approach
The study presents a methodology developed for execution time trajectory generation for the robotic SMAW. In this methodology, while the electrode is melted the robot makes the diving movement, keeping the electric arc length constant. The trajectory is generated during execution time as a function of melting rate and independent of the welding speed, given by the welding parameters. The proposed methodology uses a variable tool center point (TCP) model where the covered electrode is considered a prismatic joint, whose displacement is determined by the melting rate.
Findings
The proposed methodology was implemented in a KUKA robot. The electrode melting rate was determined by measuring the arc voltage and the electrode holder trajectory was determined during the weld, keeping the arc length and the welding speed constant. All the obtained weld beads have the same aspect, showing the process repeatability.
Research limitations/implications
Owing to its low productivity, robotic SMAW is only suitable to certain applications.
Practical implications
With this methodology, the TCP will always be located at the tip of the electrode (melting front), allowing one to program the welding speed independently of the electrode diving speed. The diving movement is automatically performed by the robot during the welding.
Originality/value
Robotic SMAW allows dangerous applications such as underwater welding and hot tapping of pipes without human intervention during the weld.
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In this paper, results of the studies on the copper deposition on screen-printed fine-line front electrode of the solar cell were presented. The silver consumption is an important…
Abstract
Purpose
In this paper, results of the studies on the copper deposition on screen-printed fine-line front electrode of the solar cell were presented. The silver consumption is an important problem according to growing silver prices. The proposed solution of those problems might be printing of a very thin silver seed layer and subsequent copper plating. This process can be an alternative for typically used screen printing. The purpose of this study was the optimization of the finger path fabrication process to obtain required geometric of fingers for copper deposition.
Design/methodology/approach
In this paper, double-step metallization process was analyzed. The first step of an electrode formation is screen printing, the second one is copper electrodeposition. Presented investigations were focused on the optimization of the finger path fabrication process to obtain required geometric dimensions and sharp border of fingers. The morphology of the electrodes was characterized by scanning electron microscope before and after copper deposition. The X-ray analysis of elemental arrangement and cross-section profiles of fingers were made using energy-dispersive X-ray fluorescence spectrometer.
Findings
Presented investigations were focused on the optimization of the finger path fabrication process to obtain required geometric dimensions and sharp border of fingers without any silver particles. The main problem of non-uniform silver paste distribution close to the border of printed finger paths was eliminated by selection of appropriate paste and printing parameters. The obtained coatings were soft, ductile and bright.
Originality/value
The novelty of the presented approach is modification of the printing parameters, especially for copper deposition. In this paper, the reasons of the widening of electrodes during the copper deposition process is analyzed.
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Jun Qin, Shuxin Bai, Weijun Zhang, Zhuofeng Liu and Hailiang Wang
The purpose of this paper is to characterize and understand the effects of polymer binder, thixotropic agent, solvent and organic medium content on the rheological properties of…
Abstract
Purpose
The purpose of this paper is to characterize and understand the effects of polymer binder, thixotropic agent, solvent and organic medium content on the rheological properties of silver pastes for screen printing front electrode films of solar cells.
Design/methodology/approach
Dispersions of silver particles (surface modified with oleic acid) in ethyl cellulose (EC) polymer solutions with and without thixotropic agent were prepared, and yield stress values were measured by setting shear stress to characterize the inter-particle interaction strength of pastes. Steady-state flow, three interval thixotropy shear test and oscillatory measurements were conducted to study the effect of EC polymer and thixotropic agent on viscosity, structure rebuilding and viscoelastic properties of electrode pastes. The effect of solvent was studied by investigating the steady viscosity of cellulose acetate butyrate (CAB) polymer solutions and Ag dispersions.
Findings
Weak flocculation network of silver particles was produced because of depletion flocculation. Besides the interaction between thixotropic agent micelles, EC polymer also has a significant interaction with thixotropic agent. Merely increasing EC polymer or thixotropic agent content is not the best way to prevent the layer printed from laying down. The effect of solvent on the viscosity of paste is mainly attributed to the difference of hydromechanics radius and configuration of CAB polymer in solvents. With the increase of organic medium content, the properties of electrode pastes were converted from rigidity to flexibility.
Originality/value
It is still a challenge to obtain high-quality front electrode films for crystalline silicon solar cells by screen printing, because of the difficulty in reducing shadowing losses while ensuring a low series resistance and high filling factor. The paste rheological properties are the key properties related to the paste’s passing ability through the meshes and resistance of paste spreading on the substrate. Organic medium as an important component of the paste is acknowledged to be used to tailor the paste’s rheological properties and have a great role in screen printing.
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Vijay Kumar Meena and Nagahanumaiah
The purpose of this paper is to optimise the electro‐discharge machining (EDM) parameters and investigate feasibility of using direct metal laser sintering (DMLS) parts as EDM…
Abstract
Purpose
The purpose of this paper is to optimise the electro‐discharge machining (EDM) parameters and investigate feasibility of using direct metal laser sintering (DMLS) parts as EDM electrodes.
Design/methodology/approach
In this paper the effects of discharge current, pulse‐on‐time, flushing pressure are optimized for minimum tool wear rate (TWR), maximum metal removal rate (MRR) and minimum surface roughness (Ra). Taguchi‐based L9 orthogonal array has been used for performing experiments on EDM machining of EN 24 steel using DMLS electrodes. The grey relational analysis combined with ANOVA techniques have been employed to determine the optimal level as well as their significance.
Findings
Experimental results have shown that the performance characteristics of the EDM process (TWR, MRR and surface roughness) using DMLS electrode can be quantified and controlled effectively by grey relational approach presented in the study. Current is found to be the most affective parameter in EDM machining using DMLS electrode. Excessive DMLS tool (electrode) wear was also reported, which limits the use of DMLS tool for EDM machining and it has been found out that porosity (which was about 20 per cent) was one of the primary cause.
Research limitations/implications
This paper was focused on understanding the effects of important EDM parameters on three performance characteristics (TWR, MRR and surface roughness). While this study identifies that DMLS electrode wear rate is high and porosity could be one of the main cause, presently it does not cover the investigations on reducing the porosity level and its implications.
Practical implications
The DMLS material had shown huge potential to be used as EDM electrode. The current investigation established a structured experimental approach to understand the effects of EDM parameters on multi response characteristics. The results derived from this study helps to focus future research on two aspects including enriching the copper content and reducing the porosity level, thereby the benefits of lead time reduction in EDM electrode making could be realized.
Originality/value
The previous research attempts were not focussed on optimising the EDM machining process using rapid tooling electrodes. With the best of author's knowledge none of the researchers have reported these aspects especially for DMLS electrodes. Application of grey relational analysis for performance evaluation of rapid tooling‐based EDM electrodes (DMLS electrodes) appear to be completely new.
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Aarthy Prabakaran and Elizabeth Rufus
Wearables are gaining prominence in the health-care industry and their use is growing. The elderly and other patients can use these wearables to monitor their vitals at home and…
Abstract
Purpose
Wearables are gaining prominence in the health-care industry and their use is growing. The elderly and other patients can use these wearables to monitor their vitals at home and have them sent to their doctors for feedback. Many studies are being conducted to improve wearable health-care monitoring systems to obtain clinically relevant diagnoses. The accuracy of this system is limited by several challenges, such as motion artifacts (MA), power line interference, false detection and acquiring vitals using dry electrodes. This paper aims to focus on wearable health-care monitoring systems in the literature and provides the effect of MA on the wearable system. Also presents the problems faced while tracking the vitals of users.
Design/methodology/approach
MA is a major concern and certainly needs to be suppressed. An analysis of the causes and effects of MA on wearable monitoring systems is conducted. Also, a study from the literature on motion artifact detection and reduction is carried out and presented here. The benefits of a machine learning algorithm in a wearable monitoring system are also presented. Finally, distinct applications of the wearable monitoring system have been explored.
Findings
According to the study reduction of MA and multiple sensor data fusion increases the accuracy of wearable monitoring systems.
Originality/value
This study also presents the outlines of design modification of dry/non-contact electrodes to minimize the MA. Also, discussed few approaches to design an efficient wearable health-care monitoring system.
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