THESIS FOR THE DEGREE OF MASTER OF SCIENCE Advisor: Jae-Do Nam, Professor Vapor-phase Polymerized Thin Films and Seeding-polymerized Nanofibers Membranes of Poly(3,4-ethylenedioxythiophene) for Optoelectronic Applications Sungkyunkwan University Department of Polymer Science and Engineering THUY LE TRUONG THESIS FOR THE DEGREE OF MASTER OF SCIENCE Advisor: Jae-Do Nam, Professor Vapor-phase Polymerized Thin Films and Seeding-polymerized Nanofibers Membranes of Poly(3,4-ethylenedioxythiophene) for Optoelectronic Applications Sungkyunkwan University Department of Polymer Science and Engineering THUY LE TRUONG THESIS FOR THE DEGREE OF MASTER OF SCIENCE Advisor: Jae-Do Nam, Professor Vapor-phase Polymerized Thin Films and Seeding-polymerized Nanofibers Membranes of Poly(3,4-ethylenedioxythiophene) for Optoelectronic Applications The Thesis is Submitted to the Graduate School of the Sungkyunkwan University in Partial Fulfillment of the Requirements for the Degree of Master of Science in Polymer Science and Engineering (Master Program) 2007. 04 Sungkyunkwan University Department of Polymer Science and Engineering THUY LE TRUONG Approved in Partial Fulfillment of the Requirements for the Degree of Master of Science 2007. 06 CURRICULUM VITAE Personal Information Name: THUY LE TRUONG Sex: Female Home address: Dap Da Town, An Nhon District, Binh Dinh Province, Vietnam Nationality: Vietnamese Education 2005.7: Sungkyunkwan University (SKKU), South Korea. (Master of Science) Thesis: “Vapor-phase Polymerized Thin Films and Seeding-polymerized Nanofibers Membranes of Poly(3,4-ethylenedioxythiophene) for Optoelectronic Applications” instructed by professor Jae-Do Nam.
2: Chemical Technology Faculty at Hochiminh City University of Technology, Vietnam. (Bachelor of Engineering) Thesis topic: “The effect of nanoclay on the properties of polyimide films” instructed by professor Huu Nieu Nguyen. 2: Researcher- Faculty member. Department of Materials Technology, Hochiminh City University of Technology, Vietnam Working as a member of the project “Fabrication of nano carbon particles for applications in microelectronics and information recording” conducted by PhD.
List of Publication and Submitted Papers 1. Thuy Le Truong, Dong-Ouk Kim, Youngkwan Lee, Tae-Woo Lee, Jong Jin Park, Lyongsun Pu, Jae-Do Nam, Surface smoothness and conductivity control of vapor-phase polymerized poly(3,4-ethylenedioxythiophene) thin coating for flexible optoelectronic applications, Submitted to Thin Solid Films (2006). Thuy Le Truong, Youngkwan Lee, Hyouk Ryeol Choi, Ja Choon Koo, Huu Nieu Nguyen, Nguyen Dang Luong, and Jae-Do Nam, Poly(3,4-ethylenedioxythiophene) Vapor-phase Polymerization on Glass Substrate for Enhanced Surface Smoothness and Electrical, Macromolecular Research, 15 (2007). Nguyen, Le Van Thang, Doan Duc Chanh Tin, Tran Viet Toan, Nguyen Thuy Ai, Truong Thuy Le, Luu Tuan Anh, Dang Mau Chien, Vo Hong Nhan, The process of micropattern image from liquid nano carbon, Society for Imaging Science and Technology, 01 Digital Fabrication, Baltimore, 209 (2005).
List of conference presentations 1. Thuy Le Truong, Dong-Ouk Kim, Youngkwan Lee, Jae-Do Nam, Vapor-phase Thin-Film Coating of PEDOT on Polymeric Substrate for Electroluminescent Devices, 9th Science & Technology Conference of HCM City University of Technology, Vietnam, 8-11 (2005). Kim Dong-Ouk, Thuy Le Truong, Lee Pyoung Chan, Yoon Song-sik , Nam Jae-Do, Optical and Electrical Characteristics of Multi-Wall Carbon Nanotubes(MWNTs)/Poly(methyl methacrylate) Nano-composite Film, The Polymer Society of Korea, 30(2), 273, (2005). The Polymer Society of Korea, 31(1), 2PS-78, (2006).
Nam, Vapor-phase Polymerized PEDOT on PET Substrate Films, 2006 SKKU PTI-CAS CIAC Joint Symposium on Polymers, Sunkyunkwan University, May 2006. Thuy Le Truong, Huu Nieu Nguyen, Do Thanh Thanh Son, and Jae-Do Nam, Poly(3,4- ethylenedioxythiophene)/Gold Nanocomposite Thin Films, the 9th seminar on “Nanomaterials and Nanocomposites: Processing and Performance”, sponsored by AUN/SEED-net project, Japan International Cooperation Agency (JICA), 142-150, 2006. Research interests • Conducting polymer, advanced material, nanotechnology, applied chemical/physical research areas and analysis methods in chemistry and physics. • Organic Polymer Electroluminescence • Biosensors and Chemical Sensors • Polymer, Metal, and Inorganic Nanoparticle Synthesis • Self-Assembly Layer Structuring • Nanocomposite Porous Structure ACKNOWLEDGEMENTS Without the contributions of others, this research would not be possible, deeply thank you: Professor Jae-Do Nam Committee members All my colleagues from Functional Nanocomposites Laboratory All professors, and support staffs of School of Engineering, Sungkyungkwan University - Thank you very much to my dear Vietnamese friends in SKKU for all wholehearted encouragement and advice.
- To be grateful to my family in Vietnam, my Mum, my Dad, my sisters and my brothers, who always stand by and comfort me throughout my life. CONTENTS List of Tables······································································································· iii List of Schemes··································································································· iii List of Figures ····································································································· iv Part I: Surface Morphology and Conductivity Control of Vapor-phase Polymerized Poly (3,4-ethylenedioxythiophene) Thin Films for Optoelectronic Applications Abstract····················································································································································2 I.3 Oxidative Polymerization of EDOT with Fe(OTs)3 by VPP···············································11 I.4 Results and Discussions ················································································································· 14 I.2 Effect of a Weak Base·········································································································· 18 I.3 Effect of Glycerol ··············································································································· 27 I.5 Conclusions ···································································································································· 31 References············································································································································· 32 Part II: Fabrication of Porous Electrochemical Membranes Based on PEDOT Nanofibers/Au Nanoparticles ··········································································· 35 i Abstract················································································································································· 36 II.2 Experimental Section····················································································································· 40 II.1 Synthesis of PEDOT Nanofibers ···················································································· 40 II.2 Synthesis of PEDOT/Carboxylated-Au Nanoparticles Composites ······························ 40 II.3 Results and Discussions ················································································································ 41 II.5 Conclusions ··································································································································· 44 References············································································································································· 45 Abstract················································································································································· 46 ii List of Tables Tables Page Table II-1 EDX analysis of porous PEDOT/Au composites membranes ······································44 Table II-2 ICP-MS analysis of porous PEDOT/Au composites membranes··································44 List of Schemes Schemes Page Scheme I-1 The monomer repeat units of unsubstituted polythiophene and PEDOT ························ 7 Scheme I-2 Structure of Baytron P (PEDOT: PSS)·············································································· 9 Scheme I-3 Vapor-phase reaction of EDA with the ester groups of the PET films. ··························14 Scheme I-4 A proposed mechanism for the effect of pyridine on PEDOT polymerization (a) and (b) pyridine coordinates with the Fe(OTs)3 through the successive substitution of pyridine with the alcohol ligands via the unbonded electrons in N, (c) the stability of cation radical of EDOT. ···································································································24 Scheme I-5 Oxidative polymerization of EDOT in the presence of Py·············································25 Scheme II-1 Schematic representation of the gold nanoparticles replication process on the PEDOT fibers ·································································································································43 iii List of Figures Figures Page Figure I-1 Electrochemical polymerization of polythiophene····························································· 8 Figure I-2 Various applications of PEDOT························································································10 Figure I-3 Vapor-phase polymerization chamber ··············································································12 Figure I-4 XPS spectra of the untreated PET films (A), EDA-treated PET films (B), and the high- resolution XPS analysis of N1s peaks of EDA-treated PET films for different treatment times (C).
The deconvoluted peaks of the EDA-treated PET for 20 min in (C) show amine and amide N-C bonds at 399. All EDA treatments were performed at 40 oC. ··································································································15 Figure I-5 Water contact angle and surface roughness of EDA-treated PET substrate films measured as a function of the EDA treatment time. ························································16 Figure I-6 FE-SEM images of PET film surfaces treated with EDA for (A) 0, (B) 15, (C) 20, (D) 25, (E) 30 and (F) 40 minutes at 40 oC in the gas phase.
The scale bar represents 200 nm for A through E.···········································································································17 Figure I-7 Surface roughness and the surface resistivity of the PEDOT-coated PET films (A) to be compared with the conductivity and thickness of a PEDOT coating on glass substrates (B) at various molar ratios of pyridine/ Fe(OTs)3 ·····························································19 Figure I-8 The cross section of PEDOT coatings on glass substrates (B) at various molar ratios of pyridine/Fe(OTs)3 ratios: (A) 0, (B) 0.············································20 Figure I-9 AFM height profiles of PEDOT films at different Py/ Fe(OTs)3 ratios: (A) 0, (B) 0.0 ···································································································20 Figure I-10 AFM images of PEDOT-coated glass substrates at different pyridine/Fe(OTs)3 ratios: (A) 0, (B) 0.5 ·····················································································································21 Figure I-11 Transparency of PEDOT films as a function of the pyridine/Fe(OTs)3 molar ratio ········22 Figure I-12 pH of Fe(OTs)3 solution as a function of the Py concentration········································23 Figure I-13 Surface roughness and the surface resistivity of PEDOT-coated PET films (A), and the iv conductivity and thickness of PEDOT coating on glass substrates (B) as a function of glycerol concentrations at a fixed molar ratio of pyridine/Fe(OTs)3 at 0.5······················28 Figure I-14 AFM height profiles of PEDOT films at a fixed molar ratio of pyridine/Fe(OTs)3 at 0.5 for various glycerol concentrations: (A) 0, (B) 5, (C) 10, (D) 15 wt%····························29 Figure I-15 Transparency of PEDOT films for various glycerol concentrations at a fixed molar ratio of pyridine/Fe(OTs)3 at 0.5 ·······················································································30 Figure II-1 SEM image (A) and high resolution SEM image (B) of PEDOT nanofibers·················42 Figure II-1 SEM image of porous PEDOT /Au membranes······························································43 v Part I Surface Mophology and Conductivity Control of Vapor-phase Polymerized Poly(3,4-ethylenedioxythiophene) Thin Films for Optoelectronic Applications ABTRACT Surface Morphology and Conductivity Control of Vapor-phase Polymerized Poly(3,4-ethylenedioxythiophene) Thin Films for Optoelectronic Applications As with other conducting polymers, poly(3,4-ethylenedioxythiophene) is considered as a promising material for optoelectronic devices. In most of those optoelectronic applications as buffer or electrode layers, the surface and/or interface of PEDOT coating layer substantially influences mobility, quantum efficiency and stability of charge carriers as well as assembled devices. Previous studies show that the effect of dielectric surface on charge mobility is due to surface-induced morphology of polythiophene. In this sense, the vapor-phase polymerization (VPP) of PEDOT is a promising technology in various optoelectronic applications to provide a thin, uniform, and highly- conductive PEDOT coating.
However, not only the conductivity enhancement but also the surface morphology of PEDOT VPP should be further explored to be adopted in optoelectronic device. In addition, the conductivity of the PEDOT coating in relation with surface smoothness and transparency should be identified to be used as thin film coating in optoelectronic devices. In this study, our overall goal is to produce well-characterised PEDOT film for optoelectronic applications by the formation of robustly nanostructured PEDOT coating. The surface morphology of PEDOT was investigated in the vapor-phase polymerization of the thiophene monomer on a flexible polyethyleneterphthalate (PET) substrate film.
The PET surface was modified with ethylene diamine maintaining the surface roughness within 2 nm to create amine and amide groups for the enhanced hydrophilic interaction with Fe(III)-tosylate (Fe(OTs)3) and for the desirable hydrogen bonding with thiophene monomer as well as PEDOT. Polymerization rate was reduced by incorporating pyridine as a reaction retardant to control the surface roughness and conductivity of PEDOT thin films. The optimal conditions of pyridine and glycerol were found at a pyridine/Fe(OTs)3 molar ratio of 0.5 and a glycerol concentration of 4~5 wt%, respectively, 2 providing the conductivity up to 500 S/cm and the surface roughness < 2 nm. KEYWORDS: Poly(3,4-ethylenedioxythiophene); vapor-phase polymerization; Fe(III)-tosylate polyethyleneterphthalate 3 I.1 Introduction There have been many studies on poly(3,4-ethylenedioxythiophene) (PEDOT) over recent years on account of its many advantageous properties such as high conductivity, transparency and stability [1-3].
This makes PEDOT very attractive for applications including electrochromic windows [4], organic electrodes for photovoltaics [5,6] and hole transport layers of organic/polymer light emitting device [7-11]. In most of those optoelectronic applications as buffer or electrode layers, the interface with the PEDOT coating layer plays an important role in determining the operating characteristics, quantum efficiency and stability [12,13]. Polythiophene structure and morphology have been reported to be important for obtaining high charge-carrier transport characteristics [14-16]. In particular, the surface roughness of the PEDOT thin films is often required not to exceed few nanometers (< 5 nm), and a uniform composition is usually required in optoelectronic device.
Therefore, the main issues in most electronic device applications are not only the electrical conductivity but also the film surface morphology such as film thickness, surface roughness, uniformity, etc. Oxidized PEDOT can be produced in several forms using different polymerization techniques. Solution processing is most commonly be used in synthesizing PEDOT in the form of spin-coating, solvent-casting, or ink-jet printing. However, the PEDOT system is relatively insoluble in most solvents, which makes it necessary to derivatize it with soluble side chains or dope the polymer with stabilizing polyelectrolytes [17].
One of the most widely used systems is an aqueous dispersion of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS), Baytron P, which is a stable polymer system with a high transparency up to 80% [18,19]. However, the PEDOT-PSS film exhibits a relatively low electrical conductivity, ~10 S/cm [18,19], which does not meet the high conductivity requirements in most applications. In addition, according to scanning-tunneling microscope and neutron reflectivity measurements, a PSS rich layer has been found at the top of the spin-coated PEDOT-PSS films [20-22]. An excessive amount of PSS is needed to stabilize the dispersion, and thus the final PEDOT-PSS films may contain substantial amounts of PSS that segregates from the PEDOT-PSS complex.
Since PSS is an electrical insulator, the excessive PSS 4 could limit the film conductivity [20].