Photoinduced charge carrier generation in a poly(3-hexylthiophene) and methanofullerene bulk heterojunction investigated by time-resolved terahertz spectroscopy

We report on the ultrafast photoinduced charge separation processes in varying compositions of poly(3-hexylthiophene) (P3HT) blended with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Through the use of time-resolved terahertz spectroscopy, the time- and frequency-dependent complex photoconductivity is measured for samples with PCBM weight fractions (WPCBM) of 0, 0.2, 0.5, and 0.8. By analysis of the frequency-dependent complex conductivity, both the charge carrier yield and the average charge carrier mobility have been determined analytically and indicate a short (<0.2 nm) carrier mean free path and a suppressed long-range transport that is characteristic of carrier localization. Studies on pure films of P3HT demonstrate that charge carrier generation is an intrinsic feature of the polymer that occurs on the time scale of the excitation light, and this is attributed to the dissociation of bound polaron pairs that reside on adjacent polymer chains due to interchain charge transfer. Both interchain and interfacial charge transfer contribute to the measured photoconductivity from the blended samples; interfacial charge transfer increases as a function of increasing PCBM. The addition of PCBM to the polymer films surprisingly does not dramatically increase the production of charge carriers within the first 2 ps. However, charge carriers in the 0.2 and 0.5 blended films survive to much longer times than those in the P3HT and 0.8 films.     

Ultrafast photoinduced charge separation dynamics in polythiophene/SnO2 nanocomposites

We present a study of photoinduced interfacial electron transfer (ET) dynamics of SnO2 nanocrystalline thin films sensitized by polythiophene derivatives (regioregular poly(3-hexylthiophene) (P3HT) and regiorandom poly(3-undecyl-2,2'-bithiophene) (P3UBT)). ET dynamics were measured by following the dynamics of injected electrons in SnO2 and polarons in the conjugated polymer using ultrafast mid-IR transient absorption spectroscopy. The rate of electron transfer from P3HT and P3UBT to SnO2 films was determined to occur on sub-picosecond time scale (120 +/- 20 fs). In P3HT/SnO2 composite, interchain charge transfer was found to compete with and reduce the quantum efficiency of interfacial electron transfer at high polymer loading. This interchain charge separation processes can be reduced in non-regioregular polymer or at low polymer loading levels.     

Electrochemistry of tetracyanoquinodimethane polyer-modified electrodes: Effect of polymer film composition on site-site interactions

Charge transport through polymer films containing the tetracyanoquinodimethane (tcnq) structure in the polymer chain and swollen with acetonitrile solvent has been studied as a function of film composition. Variation of the film composition was achieved by synthesis of a tcnq terpolymer and by casting blended films of the tcnq polyester and an isomorphic polyester containing a benzene ring in place of the tcnq structure. Formation of uniform blends at room temperature and below was indicated for the neutral polymers, but phase separation takes place on repeated cycling of the films between the 0 and −1 oxidation states. Redox center site-site interactions were probed by following dimer formation of the tcnq^.− radical anion and by the charge transport process as measured by chronocoulometric Cottrell slopes. ESR and cyclic voltammetric data indicate that interchain, and not interchain, interactions occur in the reduced films.     

Polythiophene films on gold electrodes: a comparison of bulk and contact resistances in aqueous and organic media

Recently, developed technique for separated analysis of bulk and contact resistance was applied for the investigation of polythiophene films electropolymerized in boron trifluoride diethylether. Kinetics of polymer resistance and for the first time of the contact resistance during polymer oxidation and reduction were characterized. Influence of electrochemically controlled oxidation state on the polymer bulk and the polymer/metal contact resistance was measured in aqueous and organic environment. Variation of the electrical potential from ?0.2 to 1.1?V vs. Ag/AgCl (sat) leads to an increase of the polymer conductivity for about three orders of magnitude and to a decrease of the contact resistance for about three orders of magnitude. The potential dependence of the two resistances was different, especially at high anodic potentials. In organic solution, the change of both resistances was more than six orders of magnitude. The results were compared with electrochemical and spectroelectrochemical data, a difference in the material behavior depending on the electrolyte solvent was observed. The influence of electrical potential on polymer resistance in aqueous solution was explained quantitatively by a three-state model with the values of oxidation potential +0.3 and +1.2?V.     

Effects of packing structure on the optoelectronic and charge transport properties in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole)

Spin-coated poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) films of different molecular weights (Mn= 9-255 kg/mol), both in the pristine and annealed state, were studied in an effort to elucidate changes in the polymer packing structure and the effects this structure has on the optoelectronic and charge transport properties of these films. A model based on quantum chemical calculations, wide-angle X-ray scattering, atomic force microscopy, Raman spectroscopy, photoluminescence, and electron mobility measurements was developed to describe the restructuring of the polymer film as a function of polymer chain length and annealing. In pristine high molecular weight films, the polymer chains exhibit a significant torsion angle between the F8 and BT units, and the BT units in neighboring chains are close to one another. Annealing films to sufficiently high transition temperatures allows the polymers to adopt a lower energy configuration in which the BT units in one polymer chain are adjacent to F8 units in a neighboring chain ("alternating structure"), and the torsion angle between F8 and BT units is reduced. This restructuring, dictated by the strong dipole on the BT unit, subsequently affects the efficiencies of interchain electron transfer and exciton migration. Films exhibiting the alternating structure show significantly lower electron mobilities than those of the pristine high molecular weight films, due to a decrease in the efficiency of interchain electron transport in this structure. In addition, interchain exciton migration to low energy weakly emissive states is also reduced for these alternating structure films, as observed in their photoluminescence spectra and efficiencies.     

Polythiophene films on gold electrodes: a comparison of bulk and contact resistances in aqueous and organic media

Recently, developed technique for separated analysis of bulk and contact resistance was applied for the investigation of polythiophene films electropolymerized in boron trifluoride diethylether. Kinetics of polymer resistance and for the first time of the contact resistance during polymer oxidation and reduction were characterized. Influence of electrochemically controlled oxidation state on the polymer bulk and the polymer/metal contact resistance was measured in aqueous and organic environment. Variation of the electrical potential from −0.2 to 1.1 V vs. Ag/AgCl (sat) leads to an increase of the polymer conductivity for about three orders of magnitude and to a decrease of the contact resistance for about three orders of magnitude. The potential dependence of the two resistances was different, especially at high anodic potentials. In organic solution, the change of both resistances was more than six orders of magnitude. The results were compared with electrochemical and spectroelectrochemical data, a difference in the material behavior depending on the electrolyte solvent was observed. The influence of electrical potential on polymer resistance in aqueous solution was explained quantitatively by a three-state model with the values of oxidation potential +0.3 and +1.2 V.

     

Effect of ultraviolet radiation on a metal/polyamidine system

An increase in the optical transmission in electronic spectra for metal/poly(1,10-decamethylene-acetamidine) systems after UV irradiation is observed, in contrast to polymer and metal films investigated separately where there was no such effect. The increase is explained by changes in the distribution of the electric charge induced by UV irradiation at the metal/polymer interface in a polymer film.     

Design of aromatic copolyesters for use in microelectronic devices

The next generation of microelectronic devices will require design of new kinds of polymers which are tailored to display a dielectric constant as low as 2.0, a coefficient of thermal expansion (CTE) which matches the metal circuitry as well as the silicon substrate, moisture and chemical resistance, and dimensional stability at processing temperatures of 300-400°C which are required to form an adhesive bond between laminates. In our program, we have made significant progress in all of these areas through the use of liquid crystalline copolyesters (LCP's) laminated with a newly developed crosslinkable copolyester. In this paper, data are presented which illustrate how films and coatings of either system can be made to adhere in the solid state by interchain transesterification reactions (ITR) at the interface. Ability to foam the crosslinkable copolyester films provides direct control over the dielectric constant. The effect of pore size and distribution on the dielectric constant will be discussed. The potential to dramatically increase the melting point of the LCP's through high temperature annealing is also discussed.     

Synthesis of silver and copper nanoparticle containing a-C:Hby ion irradiation of polymers

One of the many applications of diamond like carbon (DLC) is the biocompatible coating of medical tools and implants. The most recent field of interest concerns the generation of antimicrobial activity in combination with the excellent wear resistance and biocompatibility of DLC. As has already been shown for polymers, nanoparticles of silver or copper within a carbonacious matrix have a bactericidal effect.In this work we describe a new technique to produce amorphous hydrogenated carbon films (a-C:H), which contain nanometer sized clusters of silver or copper. The hybrid deposition process is based on sol–gel synthesis of polymer films and subsequent ion-induced densification and cross-linking to form a-C:H. By thermal or UV-induced reduction of metal salts in polymer solution, colloidal metal particles are produced. In this way polymer films, already containing noble metal nanoclusters, can be deposited in a wet chemical step. Upon sol–gel deposition, the polymer is subjected to ion irradiation. Based on earlier results, the influence of ion energy on chemical and mechanical properties, as well as bonding structure is investigated. Special attention is also dedicated to ion-induced diffusion and growth as well as oxidation effects.     

Infrared spectral study of noncrystalline rodlike polymers

Oriented and unoriented films of noncrystalline, wholly-aromatic, rodlike polyamides, and polyesteramides were examined by infrared spectroscopy. The results indicate that orientation, accomplished by means of mechanical stretching, approaches 80% in both polymer classes. Examination of the NH and the CO stretching region revealed an increase in the population of nonhydrogen bonded species (plateauing at ～ 85%) as orientation increases. This unusual result may be caused by interchain steric interactions which may also be responsible for both the noncrystalline morphology and the non-lyotropic behavior exhibited by these polymers.     

二维高聚物振动谱的研究

聚乙炔和聚苯胺通常由于链间耦合比较弱 ,具有一维特性 .但在增加压力的条件下可以使其链间距b减少 ,当达到与晶格常数a相近的程度时 ,这时应考虑其晶格链间耦合作用 ,它们就具有二维复式晶格结构 ,由此会带来新的物理效应 .本文考虑了由于增压作用可以使高聚物晶格链间耦合作用增强 ,并使链间距b减少 ,当b达到与晶格常数a相比拟时 ,它们可以被看作具有二维晶格结构 .基于这种情况建立了理想的二维复式晶格链模型 ,利用晶格动力学的方法 ,计算其晶格链间及原子次近邻间的相互作用 ,借助计算机计算分别在几种晶格链耦合作用下和不同质量比时的色散关系 ,模拟色散曲线 ,讨论第一布里渊区BrillouinZone(BZ)中格波高对称线上频谱的变化 ,分析了由此会带来的新的物理效应 .     

Intrachain versus Interchain Electron Transport in Poly(fluorene‐alt‐benzothiadiazole): A Quantum‐Chemical Insight

Poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole) [F8BT], displays very different charge‐transport properties for holes versus electrons when comparing annealed and pristine thin films and transport parallel (intrachain) and perpendicular (interchain) to the polymer axes. The present theoretical contribution focuses on the electron‐transport properties of F8BT chains and compares the efficiency of intrachain versus interchain transport in the hopping regime. The theoretical results rationalize significantly lowered electron mobility in annealed F8BT thin films and the smaller mobility anisotropy (μ_∥/μ_⊥) measured for electrons in aligned films (i.e. 5–7 compared to 10–15 for holes).     

正丁胺的等离子体聚合膜性质及氢离子响应功能研究

以正丁胺为单体，采用等离子体聚合法，在盖玻片与玻璃碳及一些金属基片上得到附着性和稳定性均良好的聚合膜，红外光谱，元素分析结果和膜性质研究表明，该聚合具膜具有高度支化，交联的结构，具有良好的耐热和耐腐蚀性，以该膜为敏感材料制成的电位型化学传感器在强酸性溶液中对Ｈ＾＋离子具有超能斯特响应，且稳定性和重现性较好。     

Modification of the structure of cellulose triacetate films in the course of solvent vapor sorption

Intermolecular interaction and structure of cellulose triacetate films in the course of sorption of dimethylsulfoxide, nitromethane, and tetrachloroethane vapors were studied by Fourier IR spectroscopy, X-ray diffraction analysis, and polarization microscopy. Quantitative ratio of different types of intra- and intermolecular hydrogen bonds in polymer films was estimated. Changes in the structure of cellulose triacetate films in the course of solvent vapor sorption were discussed from the viewpoint of competition between the interchain interactions via OH and C=O groups of the macromolecules and their solvation with the solvent molecules.     

Stretchable and flexible resistive behavior of poly(3,4‐ethylenedioxythiophene):Poly(styrenesulfonate) thin film on ultra‐low modulus polydimethylsiloxane with trench‐type roughness

This study investigates the resistive behavior of rod‐coated micrometer thick films of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on ultra‐low modulus (120– 130 kPa) polydimethylsiloxane (PDMS) substrate having scratch or microtrench‐type roughness patterns. On average, the films were found to remain electrically functional up to 23% axial strain with an average increase of three times in the value of the normalized resistance. The films were also found to remain conductive up to bending diameter of 4 mm with an average increase of 1.12 times their initial resistance. The rod‐coated PEDOT:PSS films on ultra‐low modulus PDMS having microtrench‐type roughness were also found to remain functional even after 1000 bending cycles at a bending diameter of 4 mm and even smaller with an increase in resistance that was on average 1.15 times their initial resistance. The films were found to fail firstly by cracking and thereby debonding from the substrate under the application of axial strain. On the other hand, the films exhibit no delamination under bending strains. The results from this investigation suggest that the polymer–polymer laminate has potential applicability in stretchable and flexible electronics and related applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 226–233     

Effect of the Side‐Chain‐Distribution Density on the Single‐Conjugated‐Polymer‐Chain Conformation

The spatial arrangement of the side chains of conjugated polymer backbones has critical effects on the morphology and electronic and photophysical properties of the corresponding bulk films. The effect of the side‐chain‐distribution density on the conformation at the isolated single‐polymer‐chain level was investigated with regiorandom (rra‐) poly(3‐hexylthiophene) (P3HT) and poly(3‐hexyl‐2,5‐thienylene vinylene) (P3HTV). Although pure P3HTV films are known to have low fluorescence quantum efficiencies, we observed a considerable increase in fluorescence intensity by dispersing P3HTV in poly(methyl methacrylate) (PMMA), which enabled a single‐molecule spectroscopy investigation. With single‐molecule fluorescence excitation polarization spectroscopy, we found that rra‐P3HTV single molecules form highly ordered conformations. In contrast, rra‐P3HT single molecules, display a wide variety of different conformations from isotropic to highly ordered, were observed. The experimental results are supported by extensive molecular dynamics simulations, which reveal that the reduced side‐chain‐distribution density, that is, the spaced‐out side‐chain substitution pattern, in rra‐P3HTV favors more ordered conformations compared to rra‐P3HT. Our results demonstrate that the distribution of side chains strongly affects the polymer‐chain conformation, even at the single‐molecule level, an aspect that has important implications when interpreting the macroscopic interchain packing structure exhibited by bulk polymer films.     

Electrochemical Performance of Transition Metal‐Coordinated Polypyrrole: A Mini Review

The conductive polymer of polypyrrole can be acted as electroactive electrode material of supercapacitor due to reversible redox behavior and high capacitance. It usually suffers from low electrochemical stability due to the breakdown of polymer molecule chain in the long‐term charge and discharge process. The monometallic or bimetallic‐coordinated polypyrrole usually exhibits the improved electrochemical performance. The transition metal ions such as ruthenium, iron, copper and cobalt are adopted for the coordination modification. The transition metal‐coordinated polypyrrole includes the intrachain and interchain coordination structure between transition metal ion and nitrogen atom of pyrrole ring. It is able to reinforce the polymer molecule chain strength to overcome excessive volumetric swelling and shrinking during charge‐discharge process, improving the cycling stability and rate capability of polypyrrole. Accordingly, the transition metal‐coordinated polypyrrole keeps simultaneously high capacitance performance and electrochemical stability, acting as the promising conductive polymer‐based supercapacitor electrode material for effective energy storage.     

Influences of chain heterogeneity on instability of polymeric thin films: dewetting of polystyrenes, polychloromethylstyrenes and its copolymers

This study compares the stability of various polymeric thin films supported on SiO(x)/Si substrate. Dewetting behaviors of polystyrenes (PS), polychloromethylstyrenes, and random poly(styrene-co-chloromethylstyrene)s are investigated by utilizing atomic force microscopy. A systematic addition of the chloromethylstyrene (ClMS) unit into PS chain causes the increase of segment polarity, affecting interfacial and interchain interactions in thin films. It is found that stability of the polymeric films depends on two major parameters, ratio of the ClMS unit and film thickness. For approximately 5 nm thick film, the addition of only 5 mol% ClMS unit causes a drastic increase of its stability, attributed to the enhanced interfacial interactions between ClMS group and SiO(x) layer. Further increasing the ClMS mole ratio to 20, 45, and 100% is accompanied by a systematic increase of the film stability. Thicker films (thicknesses approximately 22 and approximately 45 nm) of the copolymer with 5 mol% ClMS unit exhibit rather different behavior. They are found to be less stable compared to the PS films. However, the films of copolymers with ClMS unit of 20, 45, and 100% are still much more stable than the PS films. These dewetting behaviors of the copolymers are correlated to the interfacial interactions, interchain interactions and segmental segregation in thin films.     

Metallized nanotube polymer composites via supercritical fluid impregnation

Although many metal decorated nanotubes and nanowires appear in the literature, well‐dispersed metal decorated nanotube polymer composites have rarely been reported because of the excessive density mismatch between the decorated nanotubes and polymer matrix. Here, we report a novel method to prepare well‐dispersed, highly functional, metallized nanotube polymer composites (MNPCs) that possess remarkably improved electrical conductivity and mechanical toughness. The MNPCs are prepared by supercritical fluid impregnation of an organometal compound into a premade well‐dispersed single wall carbon nanotube‐polymer composite film. The infused precursor preferentially migrates towards the nanotubes to undergo spontaneous reduction and form nanometer‐scale metal particles leading to an increase in the conductivity of the MNPC films. The environmentally friendly supercritical fluid impregnation process significantly improved the toughness of the composite films, regardless of the presence of metal. Additional functionality can be imparted into the resulting MNPC by infusing other precursors such as magnetic and catalytic metal compounds. © 2011 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys, 2012     

Optical properties of plasma polymer films with encapsulated silver particles

Plasma polymer thin films with encapsulated small metal particles were prepared by simultaneous plasma polymerization and metal evaporation. Based on transmission electron microscope (TEM) micrographs, particle size and shape were analysed on films with continuously varying filling factor. Thermal annealing causes dramatic changes of the particle size and shape. The optical (UV, VIS, NIR) properties of the films were determined by the UV-absorption of the plasma polymer and by the plasma resonance absorption of the metal particles. The changes in the transmission spectra during thermal annealing were simulated with different effective medium theories. The calculated transmission spectra were fitted to the experimental spectra.