Flash Lamp Annealing and Photoluminescence Imaging of Thin Film Silicon Solar Cells on Glass
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The University of New South Wales, School of Photovoltaics and Renewable Energy Engineering Flash Lamp Annealing and Photoluminescence Imaging of Thin Film Silicon Solar Cells on Glass A Thesis Submitted for the degree of Doctor of Philosophy Anthony Teal March 2013 Supervisors: Dr. Sergey Varlamov & Dr. Henner Kampwerth THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: Teal First name: Anthony Other name/s: Shane Abbreviation for degree as given in the University calendar: PhD School: SPREE Faculty: Engineering Title: Flash Lamp Annealing and Photoluminescence Imaging of Thin Film Silicon Solar Cells on Glass Abstract 350 words maximum: (PLEASE TYPE) This thesis is divided into three main chapters, covering Flash Lamp Annealing (FLA) experiments in Chapter 1, FLA thermal and structural simulations in Chapter 2, and Photoluminescence (PL) Imaging in Chapter 3. The first and second chapters aim to gauge the feasibility of replacing the existing belt furnace Rapid Thermal Process (RTP) with FLA for Silicon (Si) films on a glass substrate that have been crystallised by Solid Phase Crystallisation (SPC). The experimental work gives us insight into the maximum stress that the film can handle during the FLA process, as well as giving us a baseline for parameters to investigate in any future experiments. It is found that FLA with 3ms pulses and 20ms pulses are not suitable replacements for the current RTP setup because significant damage to the film is observed at lower pulse energy densities than that required to achieve an adequate level of annealing. The modelling in chapter 2 predicts that the magnitude of the stress will increase with increasing pulse duration, making successful annealing at longer pulse durations unlikely. Equipment capable of producing pulse durations above 80 milliseconds, and capable of heating the Si film to temperatures between 1350°C to 1400°C does not currently exist. For this reason these pulse durations have not been investigated, but a basic design guide on how longer pulse durations could be produced is provided. The third chapter concentrates on PL Imaging of thin film Silicon Solar cells on glass. PL Imaging allows a noncontact method of characterising the quality of the Silicon film at various stages of the production process. Through PL Imaging, it was discovered that there is a large variation in material quality from sample to sample, as well as within the same sample. It is also found that the PL signal is wavelength dependent, and through modelling of cell parameters in PC1D, we can use this wavelength dependence to infer a minority carrier lifetime on low quality Si material. Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all property rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstracts International (this is applicable to doctoral theses only). ……………………………………………… ……………………………………..…… ……….……………………...…….… Signature Witness Date The University recognises that there may be exceptional circumstances requiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years must be made in writing. Requests for a longer period of restriction may be considered in exceptional circumstances and require the approval of the Dean of Graduate Research. FOR OFFICE USE ONLY Date of completion of requirements for Award: THIS SHEET IS TO BE GLUED TO THE INSIDE FRONT COVER OF THE THESIS - 1 - Originality Statement I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged. Signed: ................................................... Date: ................................................... Copyright Statement I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation. Signed: ................................................... Date: ................................................... Authenticity Statement I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format. Signed: ................................................... Date: ................................................... - 2 - Acknowledgements First and foremost I would like to thank my wife Alex. As well as tolerating the late- night work sessions and whole weekends tied up with writing, she has been a source of constant support, encouragement and inspiration. I am very grateful to her for all that she has done and continues to do, and I love her with all my heart. I would also like to thank my Mum and Dad for all their support. They have always encouraged me with whatever endeavours I choose to pursue. Their financial support in the earlier years is also very much appreciated. More than a few dollars were ‘borrowed’ from them while I was a poor University Student in Melbourne and in Sydney, allowing me to follow my dreams. The most influential person in my PhD was my supervisor, Dr Sergey Varlamov. Firstly, he took me on as a student when I was looking for a topic, and was able to draw on my previous work with lasers and flash lamps, while guiding me through the intricacies of thin film Si solar cells. I cannot show enough admiration for the efforts Dr Varlamov put in on my behalf. Without his support, my venture into the world of research would have been short-lived. For the flash lamp annealing work, I would like to thank Prof. Skorupa of FZDR in Germany. When I contacted him with a request to use his Flash Lamp equipment, he was able to provide valuable reading material and guidance as to what processing parameters would be optimal for our samples. As the experiments continued, Prof. Skroupa was very gracious with allocating time for us on the flash lamp equipment, and seeing that our samples were processed. I would also like to thank Thomas Schumann of FZDR, who did the FLA processing of our samples. I was lucky enough to spend time with Thomas at the Sub-Therm Conference in 2011, and the informal discussions I had with him were invaluable in learning the actual process of Flash Lamp Annealing, which cannot be learnt from a book. The Photoluminescence Imaging of thin film Si solar cells part of this thesis began as a way of characterising some of our more damaged FLA samples, as contacting densely cracked films is extremely difficult. Initial work had already begun by the time I started working on the topic, with much headway being made by Dr. Mark Keevers and Dr. - 3 - Oliver Kunz. After a few failed attempts at making a PL excitation source suitable for thin film Si, design input from both Mark and Oliver was incorporated into a system that proved more than adequate for the application. Before I began work on PL Imaging, an introduction to PL imaging was given to me by Yael Augarten. Yael saw the potential for PL imaging on thin films long before I did, and provided the knowledge base to investigate it. PL imaging would definitely not be a part of my thesis had I not shared an office with Yael. Once the investigations were underway and SPREE had moved to the TETB building, I found my desk close to that of Mattias Juhl. Conversations with Mattias helped to develop my ideas and the PL work immensely, and I am grateful for his input. I must also acknowledge the efforts of all the people at CSG solar, now SunTech R&D Australia. When I needed training on how to do various processing steps, Kyung Kim, Daniel Ong and Patrick Campbell were always available to assist. In the workshop, the assistance of Graham Lennon was very helpful in designing and manufacturing many of the custom parts needed for PL Imaging of thin films. And to my fellow students: Bonne, Chaho, Jae, Jialiang, Jono, Mark, Miga and Wei. Getting to know you was an added bonus to studying thin film Si Solar Cells, and the help you all provided made the task of completing a PhD fun and interesting.