Showing papers on "Conductive polymer published in 2001"

Plastic Solar Cells

Abstract: Recent developments in conjugated-polymer-based photovoltaic elements are reviewed. The photophysics of such photoactive devices is based on the photo-induced charge transfer from donor-type semiconducting conjugated polymers to acceptor-type conjugated polymers or acceptor molecules such as Buckminsterfullerene, C60. This photo-induced charge transfer is reversible, ultrafast (within 100 fs) with a quantum efficiency approaching unity, and the charge-separated state is metastable (up to milliseconds at 80 K). Being similar to the first steps in natural photosynthesis, this photo-induced electron transfer leads to a number of potentially interesting applications, which include sensitization of the photoconductivity and photovoltaic phenomena. Examples of photovoltaic architectures are presented and their potential in terrestrial solar energy conversion discussed. Recent progress in the realization of improved photovoltaic elements with 3 % power conversion efficiency is reported.

2.5% efficient organic plastic solar cells

Abstract: We show that the power conversion efficiency of organic photovoltaic devices based on a conjugated polymer/methanofullerene blend is dramatically affected by molecular morphology. By structuring the blend to be a more intimate mixture that contains less phase segregation of methanofullerenes, and simultaneously increasing the degree of interactions between conjugated polymer chains, we have fabricated a device with a power conversion efficiency of 2.5% under AM1.5 illumination. This is a nearly threefold enhancement over previously reported values for such a device, and it approaches what is needed for the practical use of these devices for harvesting energy from sunlight.

"Synthetic Metals": A Novel Role for Organic Polymers (Nobel Lecture).

Abstract: Since the initial discovery in 1977, that polyacetylene (CH)(x), now commonly known as the prototype conducting polymer, could be p- or n-doped either chemically or electrochemically to the metallic state, the development of the field of conducting polymers has continued to accelerate at an unexpectedly rapid rate and a variety of other conducting polymers and their derivatives have been discovered. Other types of doping are also possible, such as "photo-doping" and "charge-injection doping" in which no counter dopant ion is involved. One exciting challenge is the development of low-cost disposable plastic/paper electronic devices. Conventional inorganic conductors, such as metals, and semiconductors, such as silicon, commonly require multiple etching and lithographic steps in fabricating them for use in electronic devices. The number of processing and etching steps involved limits the minimum price. On the other hand, conducting polymers combine many advantages of plastics, for example, flexibility and processing from solution, with the additional advantage of conductivity in the metallic or semiconducting regimes; however, the lack of simple methods to obtain inexpensive conductive polymer shapes/patterns limit many applications. Herein is described a novel, simple, and cheap method to prepare patterns of conducting polymers by a process which we term, "Line Patterning".

Ionic conductivity in crystalline polymer electrolytes

Abstract: Polymer electrolytes are the subject of intensive study, in part because of their potential use as the electrolyte in all-solid-state rechargeable lithium batteries. These materials are formed by dissolving a salt (for example LiI) in a solid host polymer such as poly(ethylene oxide) (refs 2, 3, 4, 5, 6), and may be prepared as both crystalline and amorphous phases. Conductivity in polymer electrolytes has long been viewed as confined to the amorphous phase above the glass transition temperature, Tg, where polymer chain motion creates a dynamic, disordered environment that plays a critical role in facilitating ion transport. Here we show that, in contrast to this prevailing view, ionic conductivity in the static, ordered environment of the crystalline phase can be greater than that in the equivalent amorphous material above Tg. Moreover, we demonstrate that ion transport in crystalline polymer electrolytes can be dominated by the cations, whereas both ions are generally mobile in the amorphous phase. Restriction of mobility to the lithium cation is advantageous for battery applications. The realization that order can promote ion transport in polymers is interesting in the context of electronically conducting polymers, where crystallinity favours electron transport.

Surface modification of neural recording electrodes with conducting polymer/biomolecule blends

Abstract: The interface between micromachined neural microelectrodes and neural tissue plays an important role in chronic in vivo recording Electrochemical polymerization was used to optimize the surface of the metal electrode sites Electrically conductive polymers (polypyrrole) combined with biomolecules having cell adhesion functionality were deposited with great precision onto microelectrode sites of neural probes The biomolecules used were a silk-like polymer having fibronectin fragments (SLPF) and nonapeptide CDPGYIGSR The existence of protein polymers and peptides in the coatings was confirmed by reflective microfocusing Fourier transform infrared spectroscopy (FTIR) The morphology of the coating was rough and fuzzy, providing a high density of bioactive sites for interaction with neural cells This high interfacial area also helped to lower the impedance of the electrode site and, consequently, to improve the signal transport Impedance spectroscopy showed a lowered magnitude and phase of impedance around the biologically relevant frequency of 1 kHz Cyclic voltammetry demonstrated the intrinsic redox reaction of the doped polypyrrole and the increased charge capacity of the coated electrodes Rat glial cells and human neuroblastoma cells were seeded and cultured on neural probes with coated and uncoated electrodes Glial cells appeared to attach better to polypyrrole/SLPF-coated electrodes than to uncoated gold electrodes Neuroblastoma cells grew preferentially on and around the polypyrrole/CDPGYIGSR-coated electrode sites while the polypyrrole/CH(3)COO(-)-coated sites on the same probe did not show a preferential attraction to the cells These results indicate that we can adjust the chemical composition, morphology, electronic transport, and bioactivity of polymer coatings on electrode surfaces on a multichannel micromachined neural probe by controlling electrochemical deposition conditions

Electronic transport properties of conducting polymers and carbon nanotubes

Abstract: We review and compare electronic transport in different types of conducting polymer: conjugated organic polymers, the inorganic polymer polysulphur nitride, alkali-metal fulleride polymers, and carbon nanotubes. In each case, the transport properties show some unusual features compared to conventional metals. In conjugated organic conducting polymers, electronic transport shows a systematic pattern involving both metallic and non-metallic character. We discuss the physical conduction processes that can account for this behaviour. Key roles are played by the metal-semiconductor transition as the doping level is varied, and by the limited size of crystalline regions in the polymers, which gives rise to heterogeneous conduction. Transport data provide indirect evidence that the intrinsic conductivity of doped crystalline polyacetylene, in the absence of disordered regions, is higher than that of copper at room temperature; this high conductivity is consistent with the expected suppression of backscattering in highly anisotropic ('quasi-one-dimensional') metallic conduction. Bundles of single-wall carbon nanotubes have also been found to exhibit metallic behaviour. The temperature dependence of the conductivity of bulk samples is remarkably similar to the pattern characteristic of organic conducting polymers, typically showing a crossover from metallic to non-metallic behaviour as temperature decreases. Quantized one-dimensional conductance and other quantum effects are seen in individual nanotubes.

Enhancement of Corrosion Protection Effect in Polyaniline via the Formation of Polyaniline−Clay Nanocomposite Materials

Abstract: A series of nanocomposite materials that consisted of emeraldine base of polyaniline and layered montmorillonite (MMT) clay were prepared by effectively dispersing the inorganic nanolayers of MMT clay in organic polyaniline matrix via in-situ polymerization. Organic aniline monomers were first intercalated into the interlayer regions of organophilic clay hosts and followed by an one-step oxidative polymerization. The as-synthesized polyaniline−clay lamellar nanocomposite materials were characterized by infrared spectroscopy, wide-angle powder X-ray diffraction, and transmission electron microscopy. Polyaniline−clay nanocomposites (PCN) in the form of coatings with low clay loading (e.g., 0.75 wt %) on cold-rolled steel (CRS) were found much superior in corrosion protection over those of conventional polyaniline based on a series of electrochemical measurements of corrosion potential, polarization resistance, and corrosion current in 5 wt % aqueous NaCl electrolyte. The molecular weights of polyaniline ext...

Electrochemical Applications of Silica-Based Organic−Inorganic Hybrid Materials

Abstract: A comprehensive overview is presented on the implication of silica-based organic-inorganic hybrid materials in electrochemical science. It involves composite materials of both class I (weak bonds between the organic and inorganic components) and class II (strong chemical bonds). Starting with a description of the common designs of electrodes modified with these hybrids, the review then reports their applications in the various fields of electrochemistry, illustrating the diversity of the organically modified silicates used for this purpose. The mild chemical conditions allowed by the sol-gel process provide very versatile access to these electrochemical devices. They have found many applications in electroanalysis, including preconcentration associated with voltammetric detection, permselective coatings, electrochemical sensors, electrocatalysis, and detectors for chromatography. They were also applied as redox and conducting polymers, as solid polymer electrolytes for batteries, for the design of spectroelectrochemical and electro-chemiluminescence devices, and in the field of electrochemical biosensors.

A study on nanofiber-reinforced thermoplastic composites (II): Investigation of the mixing rheology and conduction properties

Abstract: This article is portion of a comprehensive study on the development of nanofiber-reinforced polymer composites for electrostatic discharge materials and structural composites. Vapor-grown carbon fibers with an average diameter of 100 nm were used as a precursor and model fiber system for carbon nanotubes. These nanofibers were purified and functionalized to provide for an open network of high-purity nanofibers. Banbury-type mixing was used to disperse the nanofibers in the polymer matrix. Rheological and microscopic analysis showed that the high shear processing of the polymer/nanofiber mixture led to a homogeneous dispersion of nanofibers with no agglomerates present and no shortening of the nanofibers. The shear thinning behavior of polymeric materials helps in the mixing of the nanofibers to form the composites. A percolation threshold for electrical conduction of 9–18 wt % was observed for the highly dispersed nanofiber networks. The electrical behavior of these materials was not affected by changes in humidity. Microscopic analysis showed highly dispersed nanofibers with no indications of porosity. These conducting polymers are well suited for electrostatic discharge applications, and might well become multifunctional materials for strength/electrical applications. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1162–1172, 2001

Conducting Polyaniline Nanotubes by Template-Free Polymerization

Abstract: Al-though significant fluorescence enhancement wasobserved, the final products were composite materialsconsisting of the PPV fibers interspersed within thephoto-cross-linked liquid crystal polymer matrices. Moregenerally, conjugated polymer nanofibers and nanotubeshave also been synthesized within the pores of ananoporous membrane

Electrochemical Characterization of Polyaniline in Nonaqueous Electrolyte and Its Evaluation as Electrode Material for Electrochemical Supercapacitors

Abstract: In this study, the performance of a polyaniline (PANI) based supercapacitor where electroactive PANI films were prepared on carbon paper electrodes from a nonaqueous solution with an organic acid (CF 3 COOH) as the proton source was investigated. The use of nonaqueous media as electrolyte led to an increase of the electroactivity window from 0.75 V in aqueous media up to 1.0 V. Low frequency capacitance, evaluated by electrochemical impedance spectroscopy, of about 150 F/g is reported. Scanning electron microscopy indicated a highly porous material for deposited charges greater than 1 C/cm 2 . Constant current charge/discharge cycling of a symmetric supercapacitor based on PANI in nonaqueous medium was performed in a two-electrode cell configuration and a loss of about 60% of the discharge capacity was demonstrated after 1000 cycles. Tetramethylammonium methanesulfonate (Me 4 NCF 3 SO 3 ) was also used instead of tetraethylammonium tetrafluoborate (Et 1 NBF 4 ) as supporting electrolyte in acetonitrile for the charge/discharge testing of the PANI-PANI capacitor. Energy and power densities of approximately 3.5 Wh/kg and 1300 W/kg, respectively, were developed by this supercapacitor for a cell voltage of I V and a discharge time of 20 s. On the other hand, an asymmetrical supercapacitor with polypyrrole and polyaniline used as positive and negative electrodes, respectively, displayed slightly improved performance. Indeed, an energy density of 5 Wh/kg and a power density of 1200 W/kg were reported for discharge time of about 20 s with 1 M Me 4 NCF 3 SO 3 /acetonitrile as electrolyte.

Conducting polymers in microelectronics

Abstract: Conjugated polymers in the nondoped and doped conducting state have an array of potential applications in the microelectronics industry. Conducting polymers are effective discharge layers as well as conducting resists in electron beam lithography, find applications in metallization (electrolytic and electroless) of plated through-holes for printed circuit board technology, provide excellent electrostatic discharge protection for packages and housings of electronic equipment, provide excellent corrosion protection for metals, and may have applications in electromagnetic interference shielding. This paper reviews some of these applications and briefly describes possible future applications of conducting polymers for use as interconnections or for electronic devices.

Systematic Conductivity Behavior in Conducting Polymers: Effects of Heterogeneous Disorder

Abstract: The conduction process in conducting polymers has some unusual features. Even for highly conducting samples, the electronic transport properties show a mixture of metallic and non-metallic character, which is most easily explained in terms of the heterogeneous morphology of the polymers. The Figure shows the characteristic temperature dependence of conductivity as doping level is increased. A key feature of the conductivity of the organic conducting polymers is its surprisingly large magnitude for materials with low carrier density and considerable disorder. For polyacetylene the inferred conductivity of the highly conducting crystalline regions can be greater than that of copper. However, the temperature dependence of the conductivity shows non-metallic sign over a wide range of temperatures in virtually all conducting polymers—a change to metallic sign occurs only at higher temperatures and only in some polymers. This behavior is compared and contrasted with that of carbon nanotubes (which can also be regarded as conducting polymers) and of amorphous conventional metals. The measured conductivities of organic polymers and single-wall carbon nanotube networks are analyzed in terms of a heterogeneous model that gives a good account of the data. The granularity of the superconductivity recently discovered in polythiophene films is also consistent with this heterogeneous model.

Sonochemical synthesis of amorphous Cu andnanocrystalline Cu2O embedded in a polyaniline matrix

Abstract: Composite materials containing amorphous Cu nanoparticles and nanocrystalline Cu2O embedded in polyaniline matrices have been prepared by a sonochemical method. These composite materials were obtained from the sonication of copper(II) acetate when aniline or 1% v/v aniline–water was used as solvent. Mechanisms for the formation of these products are proposed and discussed. The physical and thermal properties of the as-prepared composite materials are presented. A band gap of 2.61 eV is estimated from optical measurements for the as-prepared Cu2O in polyaniline.

Anode modification in organic light-emitting diodes by low-frequency plasma polymerization of CHF3

Abstract: Plasma polymerization of CHF3 at low frequencies was utilized for anode modification in organic light-emitting diodes. The polymerized fluorocarbon films have a high ionization potential and a relatively low resistivity. The devices with a polymer-coated anode of indium–tin–oxide exhibited enhanced hole injection and superior operational stability.

Electrochemical syntheses of highly ordered macroporous conducting polymers grown around self-assembled colloidal templates

Abstract: Three-dimensional highly ordered macroporous conducting polymer films were prepared using a self-assembled colloidal template based on poly(styrene) latex spheres. Poly(pyrrole), poly(aniline) and poly(bithiophene) were polymerised electrochemically and the polymer grown through the interstitial spaces between poly(styrene) latex spheres (0.5 µm or 0.75 µm in diameter) self-assembled in a close-packed array on gold substrates. The latex sphere template was subsequently removed by dissolution in toluene. Regular pore sizes and interconnected channels within the conducting polymer films were evident from scanning electron microscopy studies. The pore sizes for the conducting polymers studied were related to the dimensions of poly(styrene) spheres used as the template. Evidence for shrinkage of the structure was found for some polymers studied.

Conducting polyaniline composite: a reusable sensor material for aqueous ammonia

Abstract: The present paper reports about polyaniline–(acrylonitrile–butadiene–styrene) composite film as a sensor material for aqueous ammonia. The resistance change of the composite film on exposure to different concentrations of aqueous ammonia shows its utility as a sensor material. The composite film on exposure to 10 −4 and 10 −5 N aqueous ammonia shows a well-defined response behaviour and this aspect has been utilized in designing the ammonia sensor.