Solar silicon processes: technologies, challenges, and opportunities PDF
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SOLAR SILICON PROCESSES Technologies, Challenges, and Opportunities SOLAR SILICON PROCESSES Technologies, Challenges, and Opportunities edited by Bruno Ceccaroli Eivind Øvrelid Sergio Pizzini Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2017 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed on acid-free paper Version Date: 20160419 International Standard Book Number-13: 978-1-4987-4265-8 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. 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CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging‑in‑Publication Data Names: Ceccaroli, Bruno, editor. | Øvrelid, Eivind, editor. | Pizzini, Sergio, editor. Title: Solar silicon processes : technologies, challenges, and opportunities / editors, Bruno Ceccaroli, Eivind Ovrelid, and Sergio Pizzini. Description: Boca Raton : Taylor & Francis, 2017. | “A CRC title.” | Includes bibliographical references and index. Identifiers: LCCN 2016016878 | ISBN 9781498742658 (alk. paper) Subjects: LCSH: Silicon solar cells. | Photovoltaic power generation. | Polycrystalline semiconductors. | Solar cells. Classification: LCC TK2960 .S67 2017 | DDC 621.31/244--dc23 LC record available at https://lccn.loc.gov/2016016878 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Contents Preface......................................................................................................................vii Editors .......................................................................................................................xi Contributors ...........................................................................................................xiii Chapter 1 Purity Requirements for Silicon in Photovoltaic Applications ............1 Carlos del Cañizo Nadal, Simona Binetti, and Tonio Buonassisi Chapter 2 The MG Silicon Route .......................................................................49 Eivind Øvrelid and Sergio Pizzini Chapter 3 Conventional and Advanced Purification Processes of MG Silicon .............................................................................83 Yves Delannoy, Matthias Heuer, Eivind Øvrelid, and Sergio Pizzini Chapter 4 Elkem Solar and the Norwegian PV Industry through 40 years (1975–2015) ..........................................................141 Bruno Ceccaroli and Ragnar Tronstad Chapter 5 From Conventional Polysilicon Siemens Process to Low-Energy Fluidized Bed Processes Using Silane ....................199 William C. Breneman and Stein Julsrud Chapter 6 Thermodynamic Research for the Development of Solar Grade Silicon Refining Processes ...............................................................231 Kasuki Morita Index ......................................................................................................................251 v Preface Terrestrial photovoltaics gained full credibility more than 50 years ago, with the paper by Shockley and Queisser [1], setting the physical limits of conversion efficiency for single-junction solar cells. More than half a century of systematic R&D was neces- sary for photovoltaics to build up a sound economic platform and reach an industrial scale foreseeing 400–500 GW cumulative global installed capacity for 2020, and at least 50% of worldwide electric power generation for 2050. As solar cells are predominantly made of crystalline silicon, the practical avail- ability of a low-cost silicon feedstock emerged half a century ago as a prerequisite to success. The initial assumption in favor of silicon as a semiconductor material to solar cells, enunciated in the absence of any experimental evidence, predicted that solar cells could operate with sufficient efficiency also using silicon substrates of lesser quality than electronic grade silicon. The challenge was, therefore, to define an appropriate solar silicon quality and to develop industrial processes capable of replacing the Siemens process, which was already supplying the purest grade of sili- con for solid-state semiconductors, but at a cost noncompatible in the long term with massive deployment of photovoltaics in terrestrial applications. Three main options were originally retained for replacing the Siemens process. The first was the direct upgrading of commercial, metallurgical grade silicon (MG-Si) by pyro-metallurgical and physical processes, addressing in the first instance the removal of lifetime killer impurities (mainly metals of transition elements). The second was a further improvement to the first option adding to the preparation of MG-Si, the selection of pure raw materials (quartz and carbonaceous reductants) and a suitably clean operation of the metallurgical plant, thus also addressing the removal of boron and phosphorus, the respective main acceptor and donor elements to silicon. The third was the gas phase purification of silicon using gases such as chlo- rosilanes or silane but replacing the Siemens bell jar-type reactor with less energy consuming and more productive reactors (free space or/and fluidized-bed reactors [FBRs]). In all cases, the final feedstock had to be compatible in quality with the fabrica- tion of high efficiency solar cells, meaning detailed knowledge about the effect of dopants, recombining impurities, and structural defects in the basic substrate. The three options required advanced contributions in materials science and semi- conductor physics, along with the optimization of process schemes and the devel- opment of analytical procedures able to detect and quantify impurities at the level below part per billion of atoms or less. The adventure is hopefully not yet at its ultimate stage, but already presents the potential to bring photovoltaics to a leading position as an energy resource for our world. The progress of photovoltaics, through more than half of a century, passed through a number of temporary crises of a political, financial, and industrial nature, vii viii Preface as shown in Chapters 4 and 5. These chapters take a closer look at the history of companies and give illustrative examples of how PV development was indeed dra- matically influenced by socio-political changes in Europe and in the world. The aim of this book, however, is first of all, to give a rational appraisal of the numerous R&D activities carried out in the framework of low-cost silicon feedstock programs, generally sponsored by national and international agencies. Among them, the Japanese NEDO, the US DoE, and the European Commission played a major role, as direct evidence is shown in all the following chapters. Advanced gas phase polysilicon production processes, for example, the FBR con- cept, are still making impressive progress in decreasing costs as Chapter 5 shows. Some projects at the industrial scale and others still at pilot scale present the promise to reduce the cost of silicon down to $12/kg [2]. This would set a new limit for the cost of high purity silicon. Advanced gas phase processes are now in competition with processes working on different conceptual frames, aiming at the production of solar grade silicon directly from MG-Si as described in Chapters 2 and 3. Among them, the Elkem process is the most accomplished industrial example, with an annual capacity of 6500 t/year as described in detail in Chapter 4. Following another metallurgical concept, the Canadian company Silicor has announced the construction of a plant for the produc- tion of solar silicon in Iceland, to be ready in 2018, with a production capacity of 16,000 t/year at a projected cost of $9/kg [3]. Finally, Chapter 6 covers the fundamental work carried out by Kasuki Morita and colleagues in the framework of Japanese research activities addressed at solar silicon development. The authors of this book have all actively worked for a long time in the solar sili- con field and have a profound common belief in the final success of PV. Prospectively, this success is necessary because of the finite availability of natural resources, but it is also possible thanks to the infinite supply of sun power, at least in the perspective of humanity. The authors are, therefore, truly qualified to share their critical view on the problems encountered in R&D activities on the way to solar silicon, and to sug- gest some solutions for the future. We hope to have shown, also, that the R&D activities carried out in this field were and still are an outstanding contribution to the advancement of materials science. As leading editor, I am particularly indebted to Bruno Ceccaroli and Eivind Øvrelid for having shared the editorial work with me, as well as to Simona Binetti, Bill Brenemann, Tonio Buonassisi, Carlos del Cañizo Nadal, Yves Delannoy, Matthias Heuer, Stein Julsrud, Kasuki Morita, and Ragnar Tronstad, who contrib- uted and worked hard for the success of this book. My personal gratitude goes also to Dr. Wolfgang Palz, the promoter of an invalu- able amount of R&D projects as director at the European Commission. Sergio Pizzini Preface ix REFERENCES 1. W. Shockley and H. J. Queisser, 1961. Detailed balance limit of efficiency of p–n junc- tion solar cells, J. Appl. Phys., 32, 510–519. 2. http://www.pv-magazine.com/news/details/beitrag/pilot-production-begins-on- daqos-150-millionramped-up-polysilicon-capacity_100020000/#ixzz3eYpjS L4I 3. http://www.pv-tech.org/news/silicor_materials_selects_contractor_for_low_cost_ice- land_poly_fab
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