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In-Situ Infrared Spectroscopy of Organic Electrochemical Devices

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In-Situ Infrared Spectroscopy of Organic Electrochemical Devices In-situ Infrared Spectroscopy of Organic Electrochemical Devices by Parisa Shiri B.Sc., Amirkabir University of Technology, 2014 Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Department of Chemistry Faculty of Science © Parisa Shiri 2019 SIMON FRASER UNIVERSITY Spring 2019 Copyright in this work rests with the author. Please ensure that any reproduction or re-use is done in accordance with the relevant national copyright legislation. Approval Name: Parisa Shiri Degree: Master of Science Title: In-situ Infrared Spectroscopy of Organic Electrochemical Devices Examining Committee: Chair: Dr. Hua-Zhong Yu Professor Dr. Loren Kaake Senior Supervisor Assistant Professor Dr. Byron D. Gates Supervisor Associate Professor Dr. Gary W. Leach Supervisor Associate Professor Dr. Steven Holdcroft Internal Examiner Professor Date Defended/Approved: April 15, 2019 ii Abstract Organic electrochemical transistors (OECTs) offer low voltage operation and a feasible platform for flexible, large-area, and low-cost devices, especially in the context of printed electronics. However, these devices often suffer from sluggish performance as a result of ion intercalation into the bulk of the organic semiconductor. We have characterized the time dependent behaviour of OECTs based on poly(3-hexylthiophene) (P3HT) and a poly(ethylene oxide): lithium perchlorate (PEO:LiClO4) gate dielectric using in-situ infrared spectroscopy. Because charge carriers in P3HT have a characteristic absorption in the mid infrared, we can monitor the rate of device charging and discharging spectroscopically. The dependence of the charging rate on parameters such as channel length, semiconducting polymer thickness and dielectric thickness have been investigated. Our results indicate that several distinct mechanisms are at play, with the rate limiting step being determined by device geometry. Using these results, we have also examined the effect of the structure of the counter-ion on its diffusivity in the organic semiconductor once doping occurs. Keywords: FT-IR, OECTs, electrochemical doping, ion-diffusion iii Acknowledgements First and for most I would like to thank my supervisor Dr. Loren Kaake. The door to his office was always open to me and his knowledge, patience and encouragement always lightened up the research path. I am very honored to be his first graduate student. Next I would like to thank my committee members Dr. Gary Leach and Dr. Byron Gates who provided more insight and guidance during this project. I am also grateful for the students and friends who helped me with data collection in our group especially Earl Dacanay and Brennan Hagen. I am fortunate for this chance to work with all the great staff in Chemistry department as well as 4DLabs facilities without whose help and contribution this work would not be possible. Lastly, I would like to give my heartfelt thanks to my loving family for their lifetime love and support and my dearest friends Mojo and Sparrow, who are my second family, for their unconditional love and sympathetic ear when I got weary. I would also acknowledge the support of my lab mate and friend, Nastaran Yousefi, who always provided me with extra strength and motivation to get things done. In hard days she always cheered me on and her presence and friendship was a true blessing I will never forget. iv Table of Contents Approval ............................................................................................................................ ii Abstract ............................................................................................................................ iii Acknowledgements .......................................................................................................... iv Table of Contents .............................................................................................................. v List of Tables .................................................................................................................... vi List of Figures .................................................................................................................. vii List of Acronyms ............................................................................................................... xi Chapter 1. Introduction ................................................................................................ 1 1.1. Organic Semiconducting Materials ......................................................................... 2 1.2. Polymer Electrolytes and Ion Conduction ............................................................... 6 1.3. Organic Thin Film Transistors ................................................................................ 7 1.3.1. Working Principle of OTFTs ............................................................................ 7 1.3.2. Transient Behaviour Models ............................................................................ 9 1.4. Technologies and Application ............................................................................... 12 1.4.1. OECT Based Applications ............................................................................. 12 1.4.2. Electrochemical Energy Storage ................................................................... 15 1.4.3. Electrochromic Windows and Mirrors ............................................................ 16 1.4.4. Light-emitting Electrochemical Cells ............................................................. 17 1.5. Summary .............................................................................................................. 18 Chapter 2. Experimental ............................................................................................ 20 2.1. ATR-FTIR Spectroscopy ...................................................................................... 20 2.1.1. Fourier Transform Infrared Spectroscopy ..................................................... 20 2.1.2. Attenuated Total Internal Reflection or ATR Technique ................................ 24 2.2. FTIR Setup (Hardware) ........................................................................................ 27 2.2.1. Mirror Alignment ............................................................................................ 27 2.2.2. Sample Holder and Cryostat ......................................................................... 29 2.2.3. Electronic Setup ............................................................................................ 29 2.3. Software and Data Analysis ................................................................................. 31 2.4. Sample Fabrication ............................................................................................... 31 2.5. CharacteriZation Techniques ................................................................................ 36 2.5.1. Atomic Force Microscopy (AFM) ................................................................... 36 2.5.2. Profilometry ................................................................................................... 37 Chapter 3. Results and Discussion .......................................................................... 39 Chapter 4. Future Work .............................................................................................. 52 References ..................................................................................................................... 54 Appendix. AFM and Profilometry Results .............................................................. 60 v List of Tables Table 1.1 Comparison between characteristics of organic and inorganic technologies, reproduced from Pecqueur et. al.41 .................................... 14 Table 2.1 Properties of ATR crystal materials, reproduced from Fundamentals of Fourier Transform Infrared Spectroscopy by B. C. Smith55 ..................... 27 Table 3.1 Different mechanisms of charging process and the corresponding dimension of the device ........................................................................... 43 vi List of Figures Figure 1.1 Structure and energy states of (a) neutral trans-polyacetylene and (b) radical cation on trans-polyacetyne ........................................................... 3 Figure 1.2 Absorbance spectra of polarons in RR-P3HT Reprinted with permission from Österbacka et. al. 5 Copyright 2000 The American Association for the Advancement of Science. .......................................................................... 3 Figure 1.3 Chemical structures of some conjugated polymers: (a) BenZodithiophene- thienothiophene (BDT-TT) based polymer where R=2-ethylhexyl, reproduced from Holliday et. al,11 (b) a dithienylbenZothiadiaZole(DTBT) based polymer, reproduced from Duan et. al12, (c) a bithiophenesulfonamide (BTSA) based polymer where R can be different different alkyl chains, reproduced from Eastham et. al13, (d) a polythiophene with glycolated side chains p(g2T-TT), reproduced from Rivnay et. al.14 ............................................................................................ 5 Figure 1.4 Regioregurelar and regiorandom P3AT ..................................................... 5 Figure 1.5 Examples of anions and cations in ionic liquids commonly used as ion-gel dielectric materials. Cations: 1-butyl-3-methylimidaZulium (BMIM), 1-ethyl- 3-methylimidaZulium (EMIM), 1-ethyl-2,3-dimethylimidazolium (EMMIM) and 1,3-diallylimidazolium
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