University of Connecticut OpenCommons@UConn Doctoral Dissertations University of Connecticut Graduate School 4-17-2018 Conjugated Polymer-Based Functional Materials for Wearable Electronics: Electrochromism Mengfang Li University of Connecticut - Storrs, [email protected] Follow this and additional works at: https://opencommons.uconn.edu/dissertations Recommended Citation Li, Mengfang, "Conjugated Polymer-Based Functional Materials for Wearable Electronics: Electrochromism" (2018). Doctoral Dissertations. 1738. https://opencommons.uconn.edu/dissertations/1738 Conjugated Polymer-Based Functional Materials for Wearable Electronics: Electrochromism Mengfang Li University of Connecticut, 2018 Conjugated polymers (CPs), also known as conducting polymers are polymers consisting of alternating single/double bonds along the polymer backbone. Since the discovery of conducting polymers over 30 years ago,1 they have received tremendous attention and have found a variety of applications including organic transistors, 2 OLEDs, 3 organic photovoltaics (OPVs), 4 and displays.5,6 One important property of CPs is their ability to undergo reversible redox switch from a neutral (insulting) state to an oxidized (conducting) state upon the application of an external electric current or potential difference.7 Induced by electrical stimuli, the change in electronic state of CPs is usually accompanied by a distinguishable change in optical properties, more specifically, the absorption characteristics of the materials within the visible region (400–800 nm) and in the 1 Chiang, C. K.; Fincher, C. R.; Park, Y. W.; Heeger, A. J.; Shirakawa, H.; Louis, E. J.; Gau, S. C. and MacDiarmid, A. G. Phys. Rev. Lett. 1977, 39, 1098. 2 Ha, T. J.; Sonar, P. and Dodabalapur, A. Appl. Phys. Lett. 2011, 98, 253305. 3 Kim, W. H.; Mäkinen, A. J.; Nikolov, N.; Shashidhar, R.; Kim, H. and Kafafi, Z. H. Appl. Phys. Lett. 2002, 80, 3844. 4 Zhang, F.; Johansson, M.; Andersson, M. R.; Hummelen, J. C. and Inganäs, O. Adv. Mater. 2002, 14, 662. 5 Tehrani, P.; Hennerdal, L. O.; Dyer, A. L.; Reynolds, J. R. and Berggren, M. J. Mater. Chem. 2009, 19, 1799. 6 Invernale, M. A; Ding, Y. and Sotzing, G. A. ACS Appl. Mater. Interfaces 2010, 2, 296. 7 Monk, P. M. S.; Mortimer R. J. and Rosseinsky, D. R. Electrochromism: Fundamentals and Applications; VCH: Weinheim, Germany, 1995. Mengfang Li – University of Connecticut, 2018 near-infrared (NIR) region, which allows CPs to alternate from one color to another. 8 This phenomenon is referred to as electrochromism (EC) as it is a color change in response to an applied electrical potential. This dissertation is focused on conducting polymers and electrochromic devices assembled from “in situ” method and divided into two main parts: Part I (Chapter 3,4,5) is focused on the development of gel electrolyte materials for optimization of electrochromic device properties from the “in situ” approach. Compared with conventional electrochemical deposition process, the in situ approach allows the EC monomer to polymerize inside the solid state gel electrolyte matrix, eliminating the solution step. In Chapter 3, we developed and optimized novel flexible gel electrolyte materials. Electrolyte compositions were fully investigated to maximize the performance of ECDs. A study on varying salt, solvent and their composition was carried out to obtain their effects on the electrochromic performances, such as photopic contrast, film quality, switching speed and color uniformity. An optimal electrolyte exhibiting high ionic conductivity of 1.36x10-3 S/cm and yielded ECDs with a photopic contrast of 53% on ITO glass substrate. A systematic study was carried out to compare the mechanical flexibility between gel electrolyte and ITO coated polyethylene terephthalate (PET) substrate. The optimized gel formulation was found to withstand large bending extend and provide better adhesion to the substrate which. Chapter 4 demonstrate the ability to color tune the ECD through the use of theoretical calculations. Several systems were explored to reach the neutral color by using 1) a combination of organic dye with electrochromic polymer PEDOT; 2) a combination of organic electrochromic dye with electrochromic polymers PProDOT-Me2. For system #1, we demonstrate a facile method to 8 Thakur, V. K.; Ding, G.; Ma, J.; Lee, P. S. and Lu, X. Adv. Mater. 2012, 24, 4071. ii Mengfang Li – University of Connecticut, 2018 achieve neutral color ECDs by adding a commercially available yellow dye into the gel electrolyte that contains EDOT monomer. The electropolymerization of EDOT was not interfered by the organic dye, allowing for their combinatorial effect for achieving color neutral. Optimized system yields ECDs with 30% photopic contrast and fast switching speed of 1s. For system #2, poly(2,2- dimethyl-3,4-propylenedioxythiophene) PProDOT-Me2 were demonstrated to show a neutral color transition in assembled device when using balanced amount (or intensity) of a yellow colored organic small molecule dye 4,4'-biphenyldicarboxylic acid diethyl ester (PCE). The assembled devices exhibit photopic contrast of up to 55% when assembled on ITO coated glass substrates. Chapter 5 focused on the optimization of electrochromics on UV-blocking substrates such as polycarbonates through the use of long wavelength photoinitiator. An optimal EC devices using polycarbonate substrates were able to achieve high photopic contrast of 53% and with less than 3% photopic contrast loss after 3000 cycles. Part II (Chapter 6) involves patterning of conjugated polymer PEDOT:PSS onto textile using several techniques including inkjet printing, screen printing, and a sponge roller. The resulting patterned lines showed exceptional electronic characteristics as conductive wires including sheet resistances as low as 1.8 Ohms/sq and current carrying capacity of 10 Amps/mm2. iii Conjugated Polymer-Based Functional Materials for Wearable Electronics: Electrochromism Mengfang Li B. S., The Pennsylvania State University, 2012 A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy at the University of Connecticut 2018 i Copyright by Mengfang Li 2018 ii APPROVAL PAGE Doctor of Philosophy Dissertation Conjugated Polymer-Based Functional Materials for wearable electronics: Electrochromism Presented by Mengfang Li, B.S. Major Advisor: _________________________________________________________ Gregory A. Sotzing, Ph.D. Associate Advisor: ______________________________________________________ Douglas H. Adamson, Ph.D. Associate Advisor: ______________________________________________________ Rajeswari M. Kasi, Ph.D. University of Connecticut 2018 iii I dedicate this doctoral thesis to my family and friends. For always giving me the Power and Strengths to go through the dark days and bringing me Hope and Peacefulness. iv Acknowledgements Raised from a family of in which almost every family members holds a Ph.D. degree. I have always dream of getting my own someday. When I begins my graduate study at University of Connecticut, I am not sure which area I am going to focus on. After an hour long discussion with Prof. Sotzing, I was straightaway became interested in the field of conductive polymers and its applications in electronics. Working in Dr. Sotzing’s group is one of the greatest experience I have in my academic careers and I am sincerely grateful for his motivation, guidance and support. His deep knowledge in chemistry as well as willingness to get students involved in commercial projects and business meetings truly helped us getting prepared for the industrial environment. His creative ideas and give student a lot of freedom to choose their research area which helps student to gain problem solving skills as an independent researcher. I would like to thank my associate advisors, Prof. Adamson and Prof. Kasi, for their guidance and support. I would like to thank Prof. Parnas, Prof. Shaw and Prof. Sun for their guidance through my graduate research. I also would like to thank Dr. Donna Cyr for her work on the intellectual properties and technology transfer. Special thanks to the staff member in the Institute of Materials Sciences including Laura Pinatti, Gary Lavigne, Mark Dudley and Lichun Zhang, for their helps on material characterization. It has been a great pleasure to work with the most amazing people in Prof. Sotzing’s group. I am very fortunate to have Dr. Yumin Zhu as my mentor when I first join the group. He taught me many things in the lab and got me up to speed with the research. I appreciate the support of Dr. Michael Otley, Dr. Fahad Alamer, Dr. Chris Asemota, Dr. Amrita Kumar, Dr. Aaron Baldwin, Dr. Rui Ma, Dr. Whitney Kline, Dr. Robert Lorenzini, Dr. Jose Santana, Xiaozheng Zhang and Geng Li. Last but not least, I appreciate tremendous support from my family. They have always stand v by my side and encourage me to pursue my dreams. None of these would be possible without their genuine love and support. I hereby submit the following thesis for my Doctorate of Philosophy in Polymer Science. I dedicate this work to my family and friends, without whom none of this would matter. vi List of Figures Fig. 1.1 Schematic presentation of the PEDOT benzoid structure, and the ordered quinoid structure Fig. 1.2 One step synthesis of 3,4-dimethoxythiophene Fig. 1.3 Effect of intramolecular and intermolecular parameters on the band gap of selected conjugated polymers Fig. 1.4 Method for tuning optical properties of ECPs by substitution or main chain alteration. Adapted