Programme HABISOL : Habitat Intelligent et Solaire photovoltaïque
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Acronyme/acronym : Si-X Intitulé/title : Caractérisation et compréhension de la cristallisation du SiIicium photovoltaïque: imagerie X synchrotron / Cadre/Frame : ANR HABISOL Coordination : Im2np, Nathalie Mangelinck-Noël
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Les cellules photovoltaiques (PV) sont amenées à devenir une des composantes majeures de l’habitat écologique de demain. Un élément de contexte important est que la démarche d’intégration du PV dans l’habitat s’inscrit dans un cadre de forte évolution du marché PV, dont la croissance est actuellement limitée par la disponibilité à coût raisonnable d’une matière première silicium source. Pour résoudre le problème de l’approvisionnement en silicium de qualité suffisante pour l’industrie photovoltaïque, de nombreuses équipes de part le monde travaillent sur des procédés permettant de purifier la matière première abondante que représente le silicium de qualité métallurgique sans passer par le procédé de distillation utilisé pour
En conséquence, un certain nombre de problèmes liés à la solidification de ces matériaux doivent être réexaminés avec attention même pour des procédés établis pour les matériaux en provenance de l’industrie microélectronique. C’est en particulier le cas de la problématique de la structure cristalline des lingots. Dans le silicium multicristallin, qui constitue actuellement la majeure partie du silicium utilisé pour la fabrication des cellules photovoltaïques, les propriétés photovoltaïques de la cellule sont complètement différentes en fonction de la structure de grains obtenue après élaboration. La question se pose tout particulièrement pour le procédé développé par
Ce procédé présente un certain nombre d’avantages, notamment en ce qui concerne la productivité, mais la présence de gradients de température perpendiculaires à la direction de croissance conduit à une structure de solidification à grains fins et à des densités de défauts étendus importante. Il est essentiel de contrôler la structure de grains obtenue pour les différentes qualités de silicium utilisées pour la fabrication des cellules photovoltaïques. Dans ce cadre, l’objectif du projet Si-X est d’approfondir de façon significative la compréhension des mécanismes dynamiques entrant en jeu pendant la formation de la structure cristalline du silicium multi-cristallin PV. Pour cela, nous proposons une validation expérimentale incluant des expériences à plusieurs échelles associés à des techniques de caractérisation innovantes et à des simulations tri-dimensionnelles des procédés et des structures associées. En particulier, nous développerons un dispositif unique de caractérisation in situ et en temps réel de la solidification du Si utilisant
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Photovoltaic (PV) cells will become an essential element of ecologic buildings of the future. In this respect, an important issue is that the integration of PV sources in buildings takes place as the Si-PV market suffers strong evolutions. As a matter of fact, the growth of the Si-PV market is currently limited by the availability at a reasonable cost of a solar grade silicon source. In order to solve this problem, a number of teams across the world work on alternatives to the distillation process used by the microelectronics industry for the purification of metallurgical grade silicon, which is a cheap and abundant source. Such a source material should be considered as new for the purposes of ingot and cell elaboration. As a consequence, a number of issues linked to the solidification of these materials will have to be carefully considered again even for processes well-established when using materials coming from the microelectronics industry. Such is the case of the crystalline structure of the ingots. In multi-crystalline silicon, which presently constitutes the main proportion of silicon used for the fabrication of PV cells, the PV properties are totally different as a function of the grains structure obtained after the elaboration process. The question is especially acute for the process developed by the company EMIX, which is based on an original technique for the growth of ingots using continuous pulling in a cold crucible. This process presents several advantages in particular concerning the productivity but, the unavoidable existence of strong radial temperature gradients leads to a fine grained solidification structure with a high density of extended defects. As a consequence, it is essential to control the grain structure obtained for the different silicon grades used for the fabrication of PV cells. In this frame, the objective of Si-X project is to deepen significantly the understanding of the dynamical mechanisms present during the formation of the crystalline structure of multi-crystalline PV silicon. With this objective, we propose an experimental validation including various scale experiments with innovative characterisation methods coupled with 3D simulations of the processes and associated structures. In particular, we will develop a unique device using X-ray imaging system for X-ray radiography (dynamics, growth kinetics and nucleation) and X-ray topography (crystallographic orientation, strains) to characterise in situ and in real time silicon solidification. Other experiments in the project are going from wafer moulding to industrial ingots solidification and will allow linking the experiments using X-rays which are limited to small dimensions to the industrial process. Si-X project also comprises a thorough study of the link between the crystallographic structure and the PV properties. At the end of this project, benchmark data concerning the formation and development of the grain structure in multi-crystalline Si will be available as well as a 3D simulation model of these structures. The ultimate objective is to control the solidification process in order to obtain more performing materials from the PV point of view and to reduce the production costs. |
Nathalie Mangelinck-Noël, Im2np MCA
Im2np UMR CNRS 6242 • Faculté des Sciences • Avenue Escadrille Normandie Niemen • Case 142 • F 13397 Marseille Cedex 20 • France
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Partner 2
Jean-Paul Garandet, CEA/INES
CEA/INES 50 avenue du Lac Léman, Bâtiment Puma 1, 73377 Le Bourget du lac
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Tel: +33 04 79 44 45 79
Email: jean-paul.garandet@cea.fr
Partner 3
Thierry Duffar, SIMAP
SIMAP 1340 rue de la piscine,
ENSEEG BP 73,
38402 Saint Martin d’Hères
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simap.grenoble-inp.fr |
Tel: +33 4 76 82 52 13
Email: thierry.duffar@simap.grenoble-inp.fr
Partner 4
Charles-André Gandin, CEMEF
CEMEF rue Claude Daunesse BP 207, 06904 Sophia Antipolis Cedex
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www.cemef.mines-paristech.fr |
Tel: +33 4 93 95 74 27
Email: charles-andre.gandin@mines-paristech.fr
Partner 5
Florine Boulle, EMIX
EMIX Parc d’Activités de
Email: fboulle@emix.fr
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Partner 6
José Baruchel, ESRF
ESRF BP 220 38043
Email: baruchel@esrf.fr
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Partner 7
Eivind Ovrelid, SINTEF
SINTEF 2 Alfred Getz Veg 7034
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Tel: +47 98283949
Email: eivind.j.ovrelid@sintef.no
The ambitious scientific objectives of the project are to provide benchmark data and to develop quantitative predictive simulations concerning the mc-Si solidification. In particular, we endeavour to deepen the understanding of the formation of the grain structure studying: the nucleation effects, the competition between different grain morphologies, the growth kinetics, the grain size, the crystallographic orientation, strains and convection interaction. The frame of the work will be extended to several grades of silicon. The benchmark data will be issued from several complementary experiments with different sample scales and complementary characterisations. The core experiments and the most original one will consist in X-ray imaging (radiography and topography) characterisation of the mc-Si solidification in situ in samples with dimensions 40mmx6mmx500µm. These experiments will provide new incepts for the understanding of the underlying physicochemical phenomena and of their dynamics.
These experiments will be directly related and compared to wafer moulding solidification performed in the frame of the project and for which the thickness dimension is equivalent. In parallel, some solidification experiments on larger scale ingots will further complement the experimental basis. The coupling between experiments and 3D numerical simulations of the grain structure in mc-Si is also an originality of the project. By cross-comparisons with the experiments, it is expected to provide a reliable, quantitative and predictive3D simulation code for the grain structure in mc-Si. Moreover, the study of the crystallisation of the different silicon grades will be coupled with PV properties characterisation performed in the project. Further to a deeper understanding of the basic phenomena, this project has for objective to contribute to the improvement and optimisation of the processes by giving a precise knowledge of the solidification parameters impact.
Description du programme de travail / Description of the program :
Task 1 Bibliography and materials definition
Leader: Jean-Paul Garandet (CEA)
Other partners involved: EMIX, IM2NP
Objectives:
The objective of this task is to establish clearly the link between the grain structure and the PV properties by a bibliographic approach and to identify the silicon grades to be studied in the frame of the project in the different experimental conditions.
Subtask 1.1: Bibliographic study of the effect of grain boundaries, twins and dislocations.
Subtask 1.2: Silicon materials
Task 2 Benchmark experiments
Leader: Nathalie Mangelinck-Noël (IM2NP)
Other partners involved:ESRF, CEA, EMIX.
Objectives:
The main objective of this task is to achieve the in situ and in real-time X-ray synchrotron imaging of the solidification of different silicon grades. To reach this objective, this task falls into two subtasks. Subtask 2.2 has the objective to design the high temperature directional solidification furnace. Apart from the high temperature constraint, the design must take into account the adaptation to the X-ray characterisation environment and more precisely to the ESRF environment. Then, subtask 2.3 comprises the definition and the realisation of the experiments.
During task 2, various container materials for the X-ray experiments in particular will be identified. The container and coating definition should be made in relation to the various crystal growth configurations (ingot or wafer moulding). Regarding container materials, wetting / reactivity issues will be first tested on small scale samples using the well-known sessile drop configuration. Larger scale experiments will be conducted on the most promising container materials, and specifically for those selected for the X-ray experiments.
The following objective of this task (subtask 2.4) is to transpose the results of the X-ray experiments to a standard laboratory configuration that will be eventually upgraded to a pilot unit for the production of wafers by moulding (wafers of typical thickness 500 µm with lateral dimensions up to 10x10 cm²).
Subtask 2.1.: Choice of container material
Subtask 2.2: Design and fabrication of the high temperature directional solidification set-up adapted to the X-ray synchrotron imaging environment.
Subtask 2.3: Definition of the ESRF experiments and achievement of the in situ and in real time X-ray synchrotron imaging of the solidification of Si at ESRF
Subtask 2.4: Wafer moulding
Task 3 Larger scale experiments
Leader: Thierry Duffar (SIMAP)
Other partners involved: EMIX, SINTEF
Objectives:
The objective of this task is to transpose the results of the X-ray experiments to standard Bridgman type laboratory set-ups allowing the growth of ingots of significant dimensions (5x5 cm2 diameter in SIMAP, 25cm in diameter in SINTEF) and to an industrial configuration on EMIX premises. This task will benefit from subtask 1.2 as identical crucible materials, coatings and alloys could be used in these solidification furnaces for comparison purposes. This task falls into three subtasks. Subtask 3.1 has the objective to perform directional solidification of mc-Si with 5x5cm2 ingots using a Peltier interface demarcation. Subtask 3.2 is dedicated to the directional solidification of round silicon ingot at the Heliosi laboratory at SINTEF (diameter 25cm and height 12cm). Lastly, in subtask 3.3, the industrial partner EMIX, will perform some ingots elaboration in an industrial scale pilot.
Subtask 3.1: Peltier interface demarcation experiments
Subtask 3.2: Directional solidification of medium scale ingots
Subtask 3.3: Industrial scale ingots elaboration at EMIX
Task 4 Development of the 3D CAFE model
Leader: Charles-André Gandin (ARMINES-CEMEF)
Other partners involved:
Objectives:
The objective of this task is to develop the 3D simulation software based on the coupling between the FE and the CA methods for application to the simulation of the mc-Si grain structure. The model developments must be compatible with parallel calculations for computations on a distributed memory multiprocessor cluster.
Subtask 4.1: Creation of a 3D CAFE model for computations on a distributed memory multiprocessor cluster
Subtask 4.2: Visualization, evaluation and testing
Task 5 Results synthesis, characterisation and feedback to industrial processes
Leader: Benoit Naït-Ali (EMIX)
Other partners involved: All
Objectives:
One of the objectives of this task is to provide new benchmark data issued from the whole bench of solidification experiments in this project with a link to the PV properties. Subtask 5.1 deals with the analysis of the X-ray imaging experiments. Subtask 5.2 deals with the standard analysis of other experiments. Subtask 5.3 is devoted to additional characterisations that will help to deepen our understanding of the phenomena. Subtask 5.4 comprises the essential PV properties measurements to be done on the materials solidified in the different devices. A clear link between the grain structure and the PV properties sustained by the whole project and also by characterisation of industrial ingots provided by EMIX will be established. The ultimate objective of this task is to compare the experimental results with the simulation model and to the industrial process. First, it will reinforce the predictive character of the simulation model by cross comparison. Second, one output will be a better understanding of the phenomena involved in the solidification of silicon for photovoltaic applications and most likely will help to give hints to improve the industrial processes.
Subtask 5.1: Exploitation of X-ray imaging experiments:
Subtask 5.2: Exploitation of other experiments:
Subtask 5.3: Additional characterisations
Subtask 5.4 Characterisations
Subtask 5.5: Comparison of experiments with simulations and validated predictive and quantitative 3D simulation model
Subtask 5.6: Feedback to EMIX industrial process
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