Flash Lamp Annealing and Photoluminescence Imaging of Thin Film Silicon Solar Cells on Glass

202 Pages·2013·2.92 MB·English

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
Flash Lamp Annealing and Photoluminescence Imaging of Thin Film Silicon Solar Cells on Glass
Title:

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.

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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).

……………………………………………… ……………………………………..…… ……….……………………...…….…
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THIS SHEET IS TO BE GLUED TO THE INSIDE FRONT COVER OF THE THESIS
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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: ...................................................
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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.
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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. I am
privileged to be colleague and friend to you all.

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“Before coming here I was confused about
this subject. Having listened to your
lecture I am still confused. But on a
higher level”
- Enrico Fermi
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Abstract
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.

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Table of Contents
Table of Contents ................................................................................................................ - 8 - 
Chapter 1 ........................................................................................................................... - 12 - 
1.1  Introduction ................................................................................................. - 13 - 
1.2  Samples Investigated ................................................................................... - 16 - 
1.3  Optimal Annealing Time at Various Temperatures .................................... - 18 - 
1.4  FLA on Wafers ............................................................................................ - 22 - 
1.5  Flash Lamp Crystallisation of thin film Silicon on Glass ........................... - 23 - 
1.6  Experimental FLA Parameters .................................................................... - 27 - 
1.6.1  Preheat Temperature ............................................................................ - 27 - 
1.6.2  Pulse Width .......................................................................................... - 29 - 
1.6.3  Pulse Shaping ....................................................................................... - 30 - 
1.6.4  Film Thickness ..................................................................................... - 38 - 
1.6.5  Multiple Pulse FLA .............................................................................. - 38 - 
1.6.6  Glass Substrates ................................................................................... - 39 - 
1.6.7  Glass Texturing .................................................................................... - 40 - 
1.7  Equipment for FLA ..................................................................................... - 41 - 
1.7.1  Commercially Available FLA Equipment ........................................... - 41 - 
1.7.2  Equipment Available for Preliminary Experiments ............................. - 42 - 
1.7.3  Equipment designed for FLA on Thin Film Silicon ............................ - 43 - 
1.8  Results of FLA experiments ........................................................................ - 52 - 
1.8.1  Level of annealing achieved ................................................................ - 53 - 
1.8.2  Mattson Tech. Results .......................................................................... - 62 - 
1.9  Damage to Silicon Films ............................................................................. - 65 - 
1.10  Discussion of FLA Experiments .............................................................. - 70 - 
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