6 results on '"Cécile Molto"'
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2. Study of photo-oxidized n-type textured silicon surface through electrochemical impedance spectroscopy
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Pierre-Philippe Grand, Arnaud Etcheberry, Cécile Molto, Anne-Marie Goncalves, Institut Lavoisier de Versailles (ILV), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), and Institut Photovoltaïque d’Ile-de-France (ITE) (IPVF)
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Materials science ,Silicon ,Renewable Energy, Sustainability and the Environment ,business.industry ,020209 energy ,chemistry.chemical_element ,02 engineering and technology ,[CHIM.MATE]Chemical Sciences/Material chemistry ,Overpotential ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Dielectric spectroscopy ,chemistry ,Etching (microfabrication) ,Ellipsometry ,0202 electrical engineering, electronic engineering, information engineering ,Materials Chemistry ,Electrochemistry ,Optoelectronics ,Crystalline silicon ,Thin film ,business ,Silicon oxide - Abstract
International audience; For crystalline silicon (c-Si) solar cells, it is useful to measure accurately the thickness of silicon oxide (SiOx) layer presents on textured c-Si surface to further adapt the fluoride-based etching treatment. Common techniques used to characterize thin films thicknesses, such as ellipsometry or profilometry, are however not suitable for highly textured surfaces. In this work, a methodology based on Electrochemical Impedance Spectroscopy (EIS) has been developed to determine the thickness of anodic SiOx on n-type textured c-Si surface. EIS measurements have been carried out on bare c-Si surface as well as on c-Si surface with various anodic SiOx thicknesses grown by photo-oxidation. The as-obtained Nyquist and Bode diagrams enabled to plot the related Mott-Schottky curves and determine the corresponding flatband potentials (Vfb). A reference standard graph giving the anodic SiOx thickness according to measured Vfb has been therefore established. A shift of Mott-Schottky curves towards higher potential values with increased anodic SiOx thickness has been shown and explained. Mott-Schottky curves of photo-oxidized silicon surfaces have demonstrated a particular shape related to the different behaviors of Si/SiOx/electrolyte device depending on the applied overpotential. These results have been used to study the etching rate of anodic SiOx in NaHF2 fluoride media.
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- 2020
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3. Investigation of dielectric layers laser ablation mechanism on n-PERT silicon solar cells for (Ni) plating process: Laser impact on surface morphology, composition, electrical properties and metallization quality
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Etienne Drahi, Muriel Bouttemy, Varun Arya, Jan Nekarda, Pierre-Philippe Grand, Arnaud Etcheberry, Cécile Molto, Jung Eun Lee, Anne-Marie Goncalves, Solène Béchu, Institut Lavoisier de Versailles (ILV), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Institut Photovoltaïque d’Ile-de-France (ITE) (IPVF), Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE), and Fraunhofer (Fraunhofer-Gesellschaft)
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Materials science ,Silicon ,Scanning electron microscope ,Energy-dispersive X-ray spectroscopy ,chemistry.chemical_element ,02 engineering and technology ,Dielectric ,010402 general chemistry ,01 natural sciences ,Fluence ,law.invention ,X-ray photoelectron spectroscopy ,law ,[CHIM]Chemical Sciences ,ComputingMilieux_MISCELLANEOUS ,Laser ablation ,Renewable Energy, Sustainability and the Environment ,business.industry ,021001 nanoscience & nanotechnology ,Laser ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Optoelectronics ,0210 nano-technology ,business - Abstract
Laser contact opening is a critical step for solar cells manufacturing and needs to be optimized to achieve high efficiencies. In this paper, laser contact opening using a picosecond laser (wavelength 355 nm, pulse duration 10 ps) has been carried out on n-PERT precursors composed of a SiOx/SiOxNy stack on the rear polished side and a SiOxNy layer on the front textured side. By varying peak fluence from 0.130 J/cm2 to 2.159 J/cm2 and spot overlapping, ninety parameters combinations have been tested to open these dielectric layers. Surface morphology characterization, before and after laser ablation, has been realized using Confocal Laser Scanning Microscopy and Scanning Electron Microscopy. Bulk and surface compositions have also been investigated by Energy Dispersive Spectroscopy and X-ray Photoelectron Spectroscopy analysis, respectively. Results have shown the existence of four separated laser impacted areas on the polished side and a related ablation mechanism is suggested. Also, electrical characterization using four probe measurements and calibrated lifetime photoluminescence revealed that electrical properties of the silicon underlying increased when post laser annealing was performed associated with no spot overlapping. Then, nickel electroless deposition has been performed and first characterizations indicate adherence issues and inhomogeneous metallization. Characterization of metallized samples revealed that these observations were closely linked to the non-homogenous surface morphology and composition after laser ablation.
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- 2019
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4. Optimization of Ni/Cu Plating Process for Silicon Solar Cells through Understanding of Underlying Electrochemical Reaction Mechanisms
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Cécile Molto, Aurélien Duchâtelet, Solène Béchu, Muriel Bouttemy, Arnaud Etcheberry, Etienne Drahi, Daniel Lincot, Pierre-Philippe Grand, and Anne-Marie Gonçalves
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To meet future energy demand and limit global warming, researchers and industrials aim to make solar technologies more efficient and cost effective. Si-wafer based photovoltaic technology accounted for about 95 % of the total production in 2017 [1] and one of the key processing step allowing to reduce cost and increase efficiency of these solar cells is the metallization step [2]. Nowadays, screen printing is the leading metallization technology as it is simple, fast and suitable for mass production. However, this method relies on silver containing pastes, an expensive metal with a fluctuating cost [3]. Moreover, screen-printing has almost reached its limitations in term of contact quality and different ways to apply metallic contacts are required for high efficiency cell architectures and advanced cells concepts. In this context, nickel copper (Ni/Cu) electrochemical metallization, also called “plating”, is under investigation as it not only gives a solution to metal cost reduction by using cheaper metals but also has the potential to overcome screen-printing limitations [4]. Indeed, Ni/Cu plating is suitable for advanced silicon solar cell architectures and, among others interests, form very thin and non-porous metallic contacts with low contact resistivity and better aspect ratio. Despite this, Ni/Cu plating requires more improvements, especially in terms of reliability and adhesion before being implemented in mass production. Plating process optimization is only achievable through a complete understanding of electrochemical reactions mechanisms involved which is the purpose of this work. We have investigated the Ni/Cu electrochemical metallization for n-PERT (Passivated Emitter Rear Totally diffused) bifacial silicon solar cells having a front textured side and rear polished side. The different steps of the Ni/Cu plating process are the following: 1) localized laser contact opening of dielectric layers using a UV picosecond laser, 2) silicon surface deoxydation to remove silicon oxide, 3) palladium activation of the silicon surface through galvanic displacement, 4) electroless nickel deposition, 5) electrolytic copper deposition, 6) final annealing to form NiSi metallic contact. Firstly, we have demonstrated that the silicon surface morphology and composition were non-homogenous after localized laser ablation over all the laser ablation conditions. Indeed, after laser ablation, silicon oxide is still present on the silicon surface with different thicknesses over the laser opened area geometry. Consequently, palladium activation appears to be non-homogeneous with a higher number of palladium particles on the border of laser opened area. Since nickel deposition rate depends on the number of palladium particles deposited, border effects of the nickel layer have been observed. Adherence and quality of the metallic contacts are thus adversely affected. Accordingly, we have investigated in details the roles of the different parameters involved in surface deoxydation and palladium galvanic displacement reactions in order to obtain a more homogeneous activated silicon surface before nickel deposition. This allowed us to control palladium deposition process by promoting palladium nucleation over growth, enabling to have more homogeneous silicon activated surface. A changer: “”is currently being done for nickel electroless deposition and copper electrolytic deposition to increase the quality of metallic contact and silicon metal interface through a better control of deposition conditions. Moreover, a direct plating route without palladium activation, which is a challenge for metallization of bifacial solar cells, will be presented. References: [1] Photovoltaics report, Fraunhofer Institute for Solar Energy Systems, ISE, Freiburg, 2018. www.ise.fraunhofer.de. [2] V.K. Bajpai, P. Pant, C.S. Solanki, Thin uniform nickel seed layer formation and its impact on Ni-Cu contact adhesion for c-Si solar cell applications, Solar Energy. 155 (2017) 62–74. doi:10.1016/j.solener.2017.06.002. [3] ITRPV Roadmap 2018, itrpv.net/Reports/Downloads/2018/ (accessed February 7, 2019). [4] M.C. Raval, C.S. Solanki, Review of Ni-Cu Based Front Side Metallization for c-Si Solar Cells, Journal of Solar Energy. (2013). doi:10.1155/2013/183812. Figure 1
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- 2019
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5. From the Lab to Scaling-up: Case Studies of Electrodeposition Processes in the Photovoltaic Industry
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Pierre Philippe Grand, Salvador Jaime, Cedric Broussillou, Aurelien Duchatelet, Cécile Molto, Anne-Marie Gonçalves, Etienne Drahi, Lubomyr Romankiw, Hariklia (Lili) Deligianni, and Daniel Lincot
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Photovoltaic (PV), with more than 300 GW of cumulative capacity installed by the end of 2016, represents about 1.5% of the world electricity production. It is now obvious that the growth of PV will not only continue but even accelerate, as a key player for the energy transition, reaching up about 5 TW by 2050, as projected by the International Energy Association. The main reason for this development is due to a reduction by 10 of PV electricity cost in ten years. This trend makes PV electricity competitive with classical fossil or nuclear electricity in many regions of the world. The decrease in cost has resulted from improvement in materials and methods, an increase in solar energy conversion efficiency and in volume production. Research and Development plays a major role in this process proposing innovation and scientific breakthroughs in existing PV technologies and introduction of new technologies. Scaling effects have played a key role in decreasing the production costs but further progress along with innovative technologies will be needed to lower costs. The comparison between thin film technologies and wafer based technologies is typical of this paradigm. Thin film technologies are basically coating technologies which are inherently better adapted for large area processing (thousands of km2) compared to slicing individual crystalline wafers and assembling them as a mosaic. However, any defect on a part of a large area process induces a huge impact on the whole panel where the slices of Silicon are sorted to produce module. Moreover, the cost reduction of the wafer technology with scaling and the industrial maturity of silicon technology is so rapid that this technology is cost leading. As a consequence, the PV industrial sector is dominated at more than 90% by Silicon solar cells. The remaining 10% is composed of vacuum based thin films. Electrodeposition, despite intrinsic advantages, with real success in industry with, among numerous other examples, damascene copper in semiconductor or permalloys in thin film head, is almost absent of this PV industrial landscape. However, introduction of plating will be easier and more probable for new cell technologies, where new investment has to be done and for which stringer requirements emerge. In this context, we will discuss and make some prospective about two case studies involving electrodeposition in PV: plating contacts on Silicon and Cu-In-Ga based plating for thin films solar cells. On Silicon PV market, Copper represents an alternative to Silver screen printing. Copper has a much lower price than Silver with an equivalent bulk resistivity. Interdigited Back Contact (IBC) and Heterojonction (HJT) solar cells with Cu plating already exists for years. Nonetheless, Cu being a lifetime killer in c-Si, a Ni diffusion barrier is usually used. This approach has been demonstrated for front side metallization, based on Light Induced Plating. The case of emerging bifacial solar cells will be specifically discussed with the use of Ni/Cu or Ni/Ag plating. The remaining challenges will be discussed, including specificity of plating on both sides simultaneously, surface roughness issue and his impact on adhesion, ghost plating linked to surface passivation defects. For producing thin film solar cells, an alternative to vacuum based deposition methods (co evaporation, sputtering), which are presently used, is to use electrodeposition or printing. We will make a comprehensive description of the scale-up of the electrodeposited CIGS precursor layers from the laboratory scale of a rotating disk electrode to a full-size 60 cm x 120 cm compatible with 1 m2/min production of solar panels. More specifically, we will discuss the different fabrication approaches for electrodeposited precursor CIGS materials, development and recycling of solution chemistries for Copper, Indium and Gallium. Resulting fabrication of solar cells will be described. We will also present applications and devices which specifically take advantage from electrodeposition approach that is localized deposition on patterned substrate. The specific mechanism of electrodeposition in microelectrode array configuration and the challenge of upscaling will be discussed. References L. Tous et al, Energy Procedia 124, 922–929 (2017). Q. Huang, et al, Journal of The Electrochemical Society, vol. 158, issue 2, 2011, D57-D61 P.-P. Grand et al, WO 2012/052657 C. Broussillou et al, IEEE, New Orleans (2015) A. Duchatelet et al, Applied Physics Letters, 109 (2016), 253901
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- 2018
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6. Understanding reaction mechanisms of electrochemical metallization processes used for silicon photovoltaic cells
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Cécile Molto, Institut Lavoisier de Versailles (ILV), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Université Paris-Saclay, and Anne-Marie Gonçalves
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Silicon ,Métallisation électrochimique ,Interfaces ,Silicium ,Photovoltaïque ,Ablation laser ,Bifacial ,[CHIM.OTHE]Chemical Sciences/Other ,Photovoltaic ,Laser ablation ,Electrochemical metallization - Abstract
In this thesis work, Ni/Cu electrochemical deposition (“plating”) is studied as an alternative to the mainstream screen-printing technique based on Ag and Al metallic pastes to produce industrial c-Si solar cells. Ni/Cu plating has the potential to improve the quality of metallic contacts and increase c-Si solar cell efficiency. The use of cheaper metals is a strong asset to reduce the production costs. However, Ni/Cu plating is still at an introductory phase and there are some issues to deal with.The goal of this thesis is to investigate the successive steps of Ni/Cu plating process for bifacial n-PERT c-Si solar cells and understand the physico-chemical phenomena involved to address the related issues.On the first step, laser ablation parameters have been optimized to selectively ablate the dielectric layers while limiting the impact on the underlying Si. An ablation mechanism has also been proposed. Next steps of deoxidation and Pd activation of Si surface have been studied in two fluoride media (HF and NaHF2). NaHF2 provided higher SiOx etching rates and better Si surface activation. Next, homogeneity issues of Ni electroless deposition have been found, highlighting the need to make the deposition in dark conditions. Poor adherence on polished surface has been observed and areas of improvement have been suggested. The impact of non-optimized annealing parameters on cells conversion efficiencies has been demonstrated. The Ni/Cu plating process has been improved similar efficiencies than those of screen-printed reference cells have been achieved.; Pour ce travail de thèse, le dépôt électrochimique de Ni/Cu est étudié en tant qu’alternative à la sérigraphie à base de pates d’Ag et Al pour métalliser les cellules solaires en silicium cristallin. Cette technique a le potentiel d’améliorer la qualité des contacts métalliques et d’augmenter l’efficacité des cellules solaires en silicium. Les métaux utilisés étant moins coûteux, une diminution des coûts de production est envisageable. Cependant, le dépôt Ni/Cu doit être amélioré pour une application industrielle dans le domaine photovoltaïque.L’objectif de cette thèse est d’étudier les différentes étapes du procédé de dépôt de Ni/Cu sur des cellules solaires n-PERT bifaciales afin de comprendre les mécanismes physicochimiques impliqués et résoudre les différents verrous relatifs à cette technique.La première étape, qui consiste à ouvrir selectivementles couches dielectriques par ablation laser, a été optimisée en choisissant des paramètres limitant l’endommagement du silicium sous-jacent. Un mécanisme d’ablation a également été proposé. La désoxydation et l’activation au palladium du silicium, ont été étudiés dans deux milieux fluorés (HF et NaHF2). De meilleurs résultats en terme de gravure du SiOx et d’activation ont été obtenus avec NaHF2. L’inhomogénité du dépôt de nickel a soulignée l’importance de réaliser ce dépôt dans l’obscurité. Une mauvaise adhérence sur surface polie a été observée et des axes d’amélioration ont été proposés. L’impact de paramètres de recuit non adaptés sur le rendement des cellules a été étudié. Un procédé de plating Ni/Cu optimisé a été developpé et des rendements similaires aux références sérigraphiées ont été obtenus.
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