Influence of Nonadiabatic Annealing on the Morphology and Molecular Structure of PEDOT−PSS Films (original) (raw)
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Macromolecular Materials and Engineering, 2017
Self-organization of conjugated polymer such as poly(3-hexylthiophene) (P3HT) causes directional anisotropy in the charge carrier mobility. In contrast to an edge-on orientation formed in thin films of P3HT made by spin coating, in this study electrospray deposition rotates the orientation while producing nanopillar structures as a result of Coulombic fission and significant evaporation of solvent from the droplets. The nanostructured films are investigated by scanning electron microscopy. Due to substantial polymerair interfaces oriented perpendicular to the substrate, P3HT molecules adopt a face-on orientation with respect to the substrate plane that is confirmed by grazing incidence X-ray diffraction. Additionally, enhanced crystallinity (29% increase) is confirmed by a redshift in the UV-vis absorption spectra. Because deposition by electrospray is a scalable nanomanufacturing method, these results inform the design of low-cost device layers for large-surface-area applications such as light emitting diodes and photovoltaics.
Polymer, 2010
Gaining a deeper understanding of the growth of poly(3,4-ethylenedioxythiophene) (PEDOT) films by vapour phase polymerisation (VPP) is essential for the rational design and optimization of such films. The VPP process was used to synthesise films of PEDOT on oxidant-coated substrates. Atomic force microscopy images showed that the morphology of the films changed considerably with time. Utilising a quartz crystal microbalance with dissipation measurement (QCM-D), we found that the kinetics of polymerisation and the viscoelastic properties of the films varied. The data reveal four distinct stages in film growth. Each stage produces a layer having different conductivity values, from a low of 276 S cm À1 to a high of 1196 S cm À1. Conductivity and electrochromic optical contrast, D%Tx, can thus be maximized by appropriate termination of the polymerisation reaction. Factors determining the polymerisation rate and changes in conductivity and optical performance are discussed.
Properties AbstrAct Purpose: The aim of this paper was to investigate changes in surface morphology and optoelectronic properties of MEH-PPV thin films. Thin films were prepared using spin coating method. Design/methodology/approach: The changes in surface topography was observed by the atomic force microscope AFM. The results of thin films roughness have been prepared in the software XEI. The UV/VIS spectrometer was used to investigate absorbance of the obtained thin films. Findings: Results and their analysis allow to conclude that the solvent, which is an important factor in spin coating technology has an influence on surface morphology and optoelectronic properties of MEH-PPV thin films. Practical implications: Known MEH-PPV optoeletronic properties and the possibility of obtaining a uniform thin film show that it can be a good material for optoelectronic and photovoltaic application. Originality/value: The paper presents some researches of MEH-PPV thin films deposited by spin c...
Development of New Nanostructurally Engineered Polymer Semiconductors for Organic Electronics
2014
The research presented in this thesis was focused on organic semiconductors and has resulted in the development of novel printable polymer semiconductors that can be used in organic thin film transistors (OTFTs) and organic photovoltaics (OPVs), or solar cells. Polymers used in OTFT applications must have particular characteristics, such as a highly ordered or crystalline structure, favoured molecular orientation, and appropriate energy levels for either hole transport (p-type semiconductors) or electron transport (n-type semiconductors). Achieving these properties requires control of the design and synthesis of the polymers through the choice of appropriate building blocks and side chain substituents. In contrast, for OPV applications, the band gap, thin film morphology, and balance of the donor's hole mobility and the acceptor's electron mobility must be finely tuned for optimal photovoltaic performance. The specific focus of the research was on a new type of donor-acceptor copolymers that have alternating electronaccepting azo units and common electron donor units (e.g., thiophene). These polymers are expected to have strong intermolecular interactions due to the donor-acceptor effect, which could lead to improved molecular organization for efficient charge carrier transport in OTFT devices. The donor-acceptor effect also creates narrow band gap polymers, which are preferred for optimum light harvesting. The polymer materials developed in this research are evaluated as channel semiconductors in OTFTs and can also be used as donors in polymer solar cells. Zs discovery of which complemented previous work conducted by the same research group. These innovative building blocks would be valuable in numerous applications, including OTFTs and OPVs. Five polymers have been created, three of which show the most promising potential for OTFT and OPV applications: P1-DTA-BTV, P5-DTAE-BT, and P6-DTAE-TT. All of these copolymers have been synthesized via Stille coupling reaction. The first copolymer, P1-DTA-BTV, which exhibits a small band gap of 1.13 eV, with HOMO and LUMO energy levels of-5.21 eV and-4.08 eV, respectively, is suitable for both OTFT devices and OPV applications. P5-DTAE-BT and P6-DTAE-TT, on the other hand, are characterized by broader band gaps of 1.29 eV and 1.32 eV, respectively, and their average HOMO and LUMO energy levels are-5.43 eV,-4.20 eV, and-5.40 eV,-4.00 eV, respectively. It has been experimentally demonstrated that the presence of an ester group in the (E)-1,2-di(thiazol-2-yl)diazene DTA monomer helps lower the LUMO energy level, creating the broad band gap revealed in the (E)-bis(2-octyldodecyl) 2,2'-(diazene-1,2-diyl)bis(thiazole-4-carboxylate) DTAE copolymer results, and making the P5iv DTAE-BT D-A copolymer an n-type semiconductor, which is very useful for the applications mentioned above. The polymers were characterized by Differential Scanning Calorimetry DSC, Thermal Gravimetric Analysis TGA, Ultraviolet-Visible Spectrometry UV-Vis, Cyclic Voltammetry CV, Atomic Force Microscopy AFM, and X-Ray Diffraction XRD. v I would like to thank my supervisor, Professor Yuning Li, for his encouragement, guidance, and invaluable assistance during my studies. I would also like to express my gratitude to Wei Hong, Chang Guo, and Bin Sun for their help with the characterizations and device performance. Many thanks go to Jesse Quinn, who has had great contributions to some parts of this project and provided extensive assistance in the laboratory. I am likewise very appreciative of my review committee, Professor Neil McManus, and Professor Aiping Yu. A own particular gratitude to my parents specially my father, a natural giver, who encouraged me to complete my studies, as well as to my brothers, Majed and Fahad, who stood by me all the way through my study and challenges, endowing me with love, confidence, and unlimited support. I give heartfelt thanks for my family; to whom I owe more gratitude than I can ever put into words. Among my sincere acknowledgements, the financial support I have received from the Saudi Arabian Ministry of Higher Education is highly appreciated.
Thin Solid Films, 2013
Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most promising conducting polymers that can be used as transparent electrode or as buffer layer for organic electronic devices. However, when used as an electrode, its conductivity has to be optimized either by the addition of solvents or by post-deposition processing. In this work, we investigate the effect of the addition of the polar solvent dimethylsulfoxide (DMSO) to an aqueous PEDOT:PSS solution on its optical and electrical properties by the implementation of the Drude model for the analysis of the measured pseudo-dielectric function by Spectroscopic Ellipsometry from the near infrared to the visible-far ultraviolet spectral range. The results show that the addition of DMSO increases significantly the film conductivity, which reaches a maximum value at an optimum DMSO concentration as it has confirmed by experimentally measured conductivity values. The post-deposition thermal annealing has been found to have a smaller effect on the film conductivity.
Electrical proprieties of self-assembled polymers prepared by spin coating route
2016
In the recent years, organic semiconductors are widely studied because they show a variety of electro-optical and electrical proprieties. Also it's easy and facile to fabricate and process such kind of materials. Which make them promising as photovoltaic and optoelectronic devices [1-3]. In this study, we characterize and investigate electrical proprieties of ITO/PPEEB/Al structure. This structure is prepared by spin-coating. First PPEEB polymer is dissolved in chloroform solvent then coated on the substrate. Coated films on glass are used for optical characterization like transmission spectra in order to extract gap energy value. The transition is observed around 420 nm which correspond to electron transition between the valence band and conduction band equal to the gap energy of polymer Eg equal to 4eV. Second ITO substrate is used for electrical characterization, the Al electrode is deposited by thermal evaporation in vacuum on the top of structure.
Insights into the Oxidant/Polymer Interfacial Growth of Vapor Phase Polymerized PEDOT Thin Films
Advanced Materials Interfaces, 2018
The technique involves heating the monomer under either atmospheric or reduced pressure conditions which, in turn, forms a vapor. The monomer vapor then undergoes condensation onto a substrate containing an oxidant layer where polymerization is initiated resulting in film formation. Such polymers, and in particular, poly(3,4-ethylenedioxythiopene) (PEDOT), have shown promise in a variety of optoelectronic applications; for example, the polymer has been used as the binder/storage/conducting medium in supercapacitors, [2] Zn-air, and Li-ion batteries. [3] PEDOT has also found its use as a hole-injecting layer in organic photovoltaic devices (OPVs), [4] organic lightemitting diodes (OLEDs), [5] as well as the optically active material in electrochromic displays [6] and camouflage plaques. [7] One of the first accounts of utilizing the VPP technique was reported [8] in the early 1990s, but it was not until the innovating work of Winther-Jensen and West, [9] in the early part of this century, with their "solvent-less" baseinhibited process that conductivities in excess of 1000 S cm −1 were routinely achieved. Since then the technique has undergone successive iterations with variants now routinely producing conductivities in excess of 1500 S cm −1. [10] The vapor phase polymerization (VPP) technique is used to produce thin films of poly(3,4-ethylenedioxythiopene) (PEDOT) in which the Fe(III)Tosylate oxidant is altered. The oxidant is changed with the addition of an amphiphilic co-polymer having different molecular weights, namely 2800 Da. and 5800 Da. Resulting PEDOT films produce conductivities of ≈1500 and ≈3000 S cm −1 respectively. Small angle X-ray diffraction (SA-XRD) indicates that the oxidant incorporating the larger molecular weight co-polymer possesses ordered structure and that this in turn helps "template" the PEDOT during film formation. The structure and composition of the bottom (i.e. initial film formation) and top (i.e. final film formation) PEDOT surfaces are studied using surface sensitive analytical techniques; small angle X-ray diffraction (SA-XRD), ultraviolet photoelectron spectroscopy (UPS), 2D grazing incidence X-ray diffraction (2D-GIXD), metastable induced electron spectroscopy (MIES) and neutral impact collision ion scattering spectroscopy (NICISS). The results indicate that the increase in conductivity using the larger molecular weight co-polymer additive is due to the film having larger lamella-and π-stacking regions in addition to doping levels which remain unchanged throughout film formation. These conclusions are further supported by results obtained on a model PEDOT:Tosylate system using density functional theory (DFT) calculations.