Conjugated Polymers in Thermoelectric Composites and Small Molecules for High Light Absorptivity

University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations Dissertations and Theses November 2015 Conjugated Polymers in Thermoelectric Composites and Small Molecules for High Light Absorptivity Murat Tonga University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/dissertations_2 Part of the Materials Chemistry Commons, Organic Chemistry Commons, and the Polymer Chemistry Commons Recommended Citation Tonga, Murat, "Conjugated Polymers in Thermoelectric Composites and Small Molecules for High Light Absorptivity" (2015). Doctoral Dissertations. 494. https://doi.org/10.7275/7506869.0 https://scholarworks.umass.edu/dissertations_2/494 This Open Access Dissertation is brought to you for free and open access by the Dissertations and Theses at ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. CONJUGATED POLYMERS IN THERMOELECTRIC COMPOSITES AND SMALL MOLECULES FOR HIGH LIGHT ABSORPTIVITY A Dissertation Presented by MURAT TONGA Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY September 2015 Department of Chemistry i © Copyright by Murat Tonga 2015 All Rights Reserved ii CONJUGATED POLYMERS IN THERMOELECTRIC COMPOSITES AND SMALL MOLECULES FOR HIGH LIGHT ABSORPTIVITY A Dissertation Presented by MURAT TONGA Approved as to style and content by: __________________________________ Paul M. Lahti, Chair __________________________________ Ricardo Metz, Member __________________________________ Kevin Kittilstved, Member __________________________________ E. Bryan Coughlin, Member _____________________________ Craig Martin, Department Head Department of Chemistry iii DEDICATION To my wife Gülen and my son Ali Eray, and to my family. iv ACKNOWLEDGEMENTS I owe my deepest gratitude to my advisor Prof. Paul M. Lahti to give me the opportunity to work with him and giving all of the direction, help and support over the past few years. His guidance helped me in all the time of research and writing of this thesis. I also express my warmest gratitude to my committee members, Professors Ricardo Metz, Kevin Kittilstved and E. Bryan Couglin for their valuable guidance and insightful comments. I would also like to thank our collaborators Prof Frank E. Karasz and Dr Ljiljana Korugic-Karasz who gave access to TE laboratory. I would also like to thank Dr Patrick S. Taylor to mentor me use TE instruments. I am grateful to Dr. Lang Wei of the Lahti group for assistance to get SEM images. I am grateful for assistance by undergraduate chemistry major researcher Christopher Borcoche of the Lahti group for obtaining a number of quantum yields and fluorescence lifetime results. I thank all Lahti group members, past and present, for their advice, and friendship. I am also grateful to Dr. Eugene Wilusz and US Army Natick Soldier Research, Development and Engineering Center (NSRDEC) for their financial support. Words cannot express how grateful I am to my mother; your prayer for me was what sustained me thus far. Last but not the least, thank you to my beloved wife Gülen for endless love and support, there would be something missing without you. v ABSTRACT CONJUGATED POLYMERS IN THERMOELECTRIC COMPOSITES AND SMALL MOLECULES FOR HIGH LIGHT ABSORPTIVITY SEPTEMBER 2015 MURAT TONGA, B.S., BOGAZICI UNIVERSITY M.S., BOGAZICI UNIVERSITY Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Paul M. Lahti Over the past several decades with increasing of global energy demand, thermoelectric materials have gained considerable attention due to their unique ability to directly convert heat to electricity. In addition to inorganic semiconductors, polymers are potential candidates for high- performance thermoelectric applications due to their intrinsic advantages such as low thermal conductivity, solution processability, and roll-to-roll production, lightweight, and flexible thermoelectric modules. This thesis provides an insight into the emerging field of organic thermoelectrics, more specifically, thermoelectric power generation based on the composites of conducting polymers (MEH-PPV, P3HT and PEDOT:PSS) and carbon nanotubes (SWNT, SWNT-COOH, SWNT-OH and MWNT). A substantial portion of my work at the graduate level has involved the composite materials of conductive polymers and carbon nanotubes (CNTs) for use in organic thermoelectrics (TE). This work comprised multiple iterations to test effects of chain length (molecular weight) and regioregularity, amount and type of CNT added, sample fabrication vi solvent, and doping duration led to substantial optimization of the TE power factors. A power factor of 148 μW m-1 K-2 was obtained in the optimized sample preparation with rr-P3HT- Rieke/50%SWnNT which is quite competitive with the PFs mentioned in section 2.3. Besides polymers, I also investigated TE properties of cross-linked network structures established from UV curable small molecules with CNTs. A variety of distinct morphological architectures -- consistent with differences in TE performances -- have been observed. I described the synthesis of new pyridinium and extended viologen molecules capturing light in the visible portion of the solar spectrum with high molar extinction coefficient (~22,000 to 278,000 M-1 cm-1) by means of intramolecular charge transfer (ICT), using electron-donor and electron-accepter groups linked through π-conjugation. Also, these compounds exhibited solvatochromic properties in absorption and emission spectra with respect to the ICT band. vii TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ............................................................................................................. v ABSTRACT .................................................................................................................................... vi LIST OF TABLES ......................................................................................................................... xii LIST OF FIGURES ...................................................................................................................... xiii LIST OF SCHEMES...................................................................................................................... xx CHAPTER 1. GENERAL BACKGROUND FOR THERMOELECTRICS ................................................... 1 1.1 Applications of the Thermoelectric Effect .......................................................................... 2 1.2 Basic Principles of Thermoelectrics .................................................................................... 3 1.2.1 Seebeck Coefficient (S) ................................................................................................. 5 1.2.2 Electrical Conductivity (σ) ............................................................................................ 6 1.2.3 Thermal Conductivity (κ) .............................................................................................. 6 1.3 Organic Thermoelectrics ..................................................................................................... 8 1.3.1 Structure Variability Effects on Thermoelectric Behavior .......................................... 10 1.3.2 Polymer Molecular Weight and Chain Length Effects ............................................... 10 1.3.3 Morphology Effects .................................................................................................... 11 1.4 Strategies for Improvement of Thermoelectric Performance ............................................ 12 1.4.1 Doping ......................................................................................................................... 12 1.4.2 Effects of Adding Carbon Nanotubes (CNTs) on Electronic Behavior of Organics .. 14 1.5 A Brief Summary of Important, Recent Developments in Organic/Polymer Based Thermoelectrics ................................................................................................................ 15 1.6 References ......................................................................................................................... 19 2. THERMOELECTRIC STUDIES OF MEH-PPV BLENDS WITH CARBON NANOTUBES ......................................................................................................................... 25 2.1 Introduction ....................................................................................................................... 25 2.2 Results and Discussion ...................................................................................................... 26 2.2.1 Basic Nomenclature and Procedures. .......................................................................... 26 viii 2.2.2 Effect of Fabrication Conditions on Thermoelectric Performance of Iodine-doped MEH-PPV Samples .................................................................................................... 27 2.2.3 Optimizing MEH-PPV TE Composite Blends with SWNTs: Effect of Doping Exposure Time ........................................................................................................... 30 2.2.4 Optimizing MEH-PPV TE Blends with SWNTs: A Diameter Effect? ....................... 34 2.2.5 Stability of Doped MEH-PPV/CNT Blends: ‘Dedoping-Redoping’ Experiments ..... 39 2.2.6 MEH-PPV Blends with MWNTs

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