Showing papers on "Conductive polymer published in 2008"

Efficient and Flexible ITO‐Free Organic Solar Cells Using Highly Conductive Polymer Anodes

Abstract: Despite the relatively low efficiencyin comparison with conventional inorganic solar cells, thepotential of roll-to-roll processing and large-area processa-bility on flexible low-cost substrates renders conjugatedpolymer-based organic solar cells (OSCs) very attractive asa cost-effective solution to the problem of energy shortage.Among the available BHJ systems, poly(3-hexylthiophene)(P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C

Air-stable inverted flexible polymer solar cells using zinc oxide nanoparticles as an electron selective layer

Abstract: The performance and stability of unencapsulated inverted bulk-heterojunction solar cells with zinc oxide (ZnO) made by different processes as the electron selective contact are compared to conventional bulk-heterojunction solar cells. The low temperature processed inverted devices using ZnO nanoparticles on indium tin oxide plastic substrates showed high power conversion efficiency of ∼3.3%. This inverted device structure possessed much better stability under ambient conditions retaining over 80% of its original conversion efficiency after 40days while the conventional one showed negligible photovoltaic activity after 4days. This is due to the improved stability at the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Ag interface.

Carbon nanotube and conducting polymer composites for supercapacitors

Abstract: Composites of carbon nanotubes and conducting polymers can be prepared via chemical synthesis, electrochemical deposition on preformed carbon nanotube electrodes, or by electrochemical co-deposition. The composites combine the large pseudocapacitance of the conducting polymers with the fast charging/discharging double-layer capacitance and excellent mechanical properties of the carbon nanotubes. The electrochemically co-deposited composites are the most homogeneous and show an unusual interaction between the polymer and nanotubes, giving rise to a strengthened electron delocalisation and conjugation along the polymer chains. As a result they exhibit excellent electrochemical charge storage properties and fast charge/discharge switching, making them promising electrode materials for high power supercapacitors.

Plasmon enhanced performance of organic solar cells using electrodeposited Ag nanoparticles

Abstract: To enhance solar harvesting in organic solar cells, uniform-sized metal nanoparticles of ∼13 nm were incorporated to the device via pulse-current electrodeposition, which is a kind of simple and quick solution process that can control the density and size of metal nanoparticles. By incorporating plasmonic Ag nanoparticles on surface modified transparent electrodes, overall power conversion efficiency was increased from 3.05% to 3.69%, mainly resulting from the improved photocurrent density as a result of enhanced absorption of the photoactive conjugate polymer due to the high electromagnetic field strength in the vicinity of the excited surface plasmons.

Polymer Solar Cells That Use Self‐Assembled‐Monolayer‐ Modified ZnO/Metals as Cathodes

Abstract: valuesoriginatefromthelossofchargecarriersthroughleakagepathsincluding pinholes in the films and the recombination andtrapping of the carriers during their transit through the cell,leading to a decrease in device performance.Modification of electrodes has been commonly employed toimprove the contact between the active organic layer andelectrodes. At the indium tin oxide (ITO) anode side, a thinbuffer layer of a conductive polymer, poly(3,4-ethylene-dioxylene thiophene):poly(styrene sulfonic acid) (PED-OT:PSS), is often used to increase the work-function of ITOfor effective hole collection.

The mechanism of the oxidative polymerization of aniline and the formation of supramolecular polyaniline structures

Abstract: Polyaniline is one of the most important conducting and responsive polymers. A molecular mechanism for the oxidation of aniline is proposed. This mechanism explains the specific features of aniline oligomerization and polymerization in various acidity ranges. The formation of polyaniline precipitates, colloids and thin films is reviewed and discussed on the basis of the chemistry of aniline oxidation. The generation of nanostructures, i.e. granules, nanotubes, nanowires and microspheres, is also considered. Oligomers containing phenazine constitutional units play an important role in self-assembly to form templates. Polyaniline chains then grow from these templates and produce the various individual morphologies. Copyright © 2008 Society of Chemical Industry

Electrochemical Sensors Based on Organic Conjugated Polymers

Abstract: Organic conjugated polymers (conducting polymers) have emerged as potentialcandidates for electrochemical sensors. Due to their straightforward preparation methods,unique properties, and stability in air, conducting polymers have been applied to energystorage, electrochemical devices, memory devices, chemical sensors, and electrocatalysts.Conducting polymers are also known to be compatible with biological molecules in aneutral aqueous solution. Thus, these are extensively used in the fabrication of accurate,fast, and inexpensive devices, such as biosensors and chemical sensors in the medicaldiagnostic laboratories. Conducting polymer-based electrochemical sensors and biosensorsplay an important role in the improvement of public health and environment because rapiddetection, high sensitivity, small size, and specificity are achievable for environmentalmonitoring and clinical diagnostics. In this review, we summarized the recent advances inconducting polymer-based electrochemical sensors, which covers chemical sensors(potentiometric, voltammetric, amperometric) and biosensors (enzyme based biosensors,immunosensors, DNA sensors).

Fast electrochemistry of conductive polymer nanotubes: synthesis, mechanism, and application.

Abstract: Conductive polymers exhibit several interesting and important properties, such as metallic conductivity and reversible convertibility between redox states. When the redox states have very different...

A Semi-transparent Plastic Solar Cell Fabricated by a Lamination Process†

Abstract: Polymer solar cells have attracted broad research interest because of their advantageous solution processing capability and formation of low-cost, flexible, and large area electronic devices. However, the efficiency of polymer solar cells is still low compared to that of inorganic solar cells. Therefore, it is a challenge to find a polymer that has all the required properties for high efficiency devices, such as strong and broad absorption, high carrier mobility, and appropriate energy levels. One possible solution to avoid the strict material requirements is to stack two or more devices with different spectral responses, which enables more efficient utilization of solar energy. Such a solution would require a semitransparent solarcell device with high efficiency in its absorption wavelength range, while high transparency would be required in the complementary wavelength range. Semitransparent solar cells are also interesting for other appealing applications, such as energy-generating color window glasses. It is desirable that such solar cell devices can be fabricated using a low-cost strategy, such as the roll-to-roll fabrication process. One critical issue in this fabrication process is how to form the active-layer/cathode mechanic and electronic contacts. The lamination process is one very promising technique to fulfill this requirement owing to its simplicity and low cost. It has been reported to produce two-layer heterojunction solar cells; however, the method is not applicable to bulk heterojunction solar cells, nor compatible with roll-to-roll fabrication process. In this Communication, an electronic glue-based lamination process combined with interface modification is presented as a one-step process for semitransparent polymer solar-cell fabrication. The finished device is metalfree, semitransparent, flexible, self-encapsulated, and highly efficient (with a maximum external quantum efficiency of 70 % and power efficiency of 3 % under AM 1.5 global 1 sun solar illumination conditions with spectral mismatch correction). This approach represents a critical step towards the ultimate goal of low-cost polymer solar cells. The device fabrication process is illustrated in Figure 1, and can be described by the following steps. In Step I, two transparent substrates coated with a transparent conductor such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), or a high conductivity polymer, etc., are selected. In Step II, one substrate is coated with a very thin buffer layer (Cs2CO3 ) to act as the low-work-function cathode, followed by coating of the active polymer layer. Step III involves the coating of conductive polymer glue to the other transparent substrate. We used modified conducting polymer poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the electronic glue, which was spin-coated to form the adhesive anode. Step IV is the lamination process: after drying both the substrates, they are laminated together by exerting force so that the two substrates are tightly glued together. During this lamination, a plastic rod with proper hardness rolls the plastic substrate to remove air bubbles. Both substrates are heated to a temperature of 105–120 °C during the lamination process, and the finished devices are then kept on the hotplate for 5–10 min for the final heat treatment. The PEDOT:PSS was purposely modified to become adhesive, so that the two separate films formed good contact at the interface, both electronically and mechanically. In this work, this adhesive and conductive PEDOT:PSS layer was obtained by doping D-sorbitol or volemitol into PEDOT:PSS, as has been successfully demonstrated in polymer light emitting diodes. However, the efficiency of such a device is too low for application. The polymer blend used in this work is regioregular poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (RRP3HT:PCBM) in 1:1 w/w ratio. The 200 nm thick polymer blend film was deposited by the slow-growth method (or solvent annealing) to enhance device efficiency. Either glass or plastic can be used as the transparent substrate. Figure 1b shows a picture of an all-plastic solar cell. The device area is ca. 40 mm. With both cathode and anode being transparent, a semitransparent polymer solar cell is formed. The transparency (T%) of the device is shown in Figure 1c, together with the solar illumination spectrum. A transparency of around 70 % was obtained in the wavelength range where polymer/PCBM has no absorption, which makes this device suitable for application in stacking devices to make full use of the solar spectrum. This device fabrication method has many advantages over the regular procedure. First of all, no thermal evaporation process is involved in the process, and each layer is coated by a low-cost and easy solution process. Second, in contrast to the reactive metal cathode in regular devices, the cathode in C O M M U N IC A IO N

A Template‐Free Method Towards Conducting Polymer Nanostructures

Abstract: Conducting polymer nanostructures have recently received special attention in nanoscience and nanotechnology because of their highly π-conjugated polymeric chains and metal-like conductivity, such that they can be regarded not only as excellent molecular wires, but also as basic units for the formation of nanodevices. Although various approaches, such as hard-template methods, soft-template methods, electrospinning technology, and so on are widely employed to synthesize or fabricate conducting polymer nanostructures and their composite nanostructures, each of the currently used methods possess disadvantages. Therefore, finding a facile, efficient, and controlled method of forming conducting polymer nanostructures is desirable. Similar to other nanomaterials, the effect of size (in these cases 1-100 nm) on the properties of the conducting polymer nanostructures must be considered. Electrical measurements of single nanotubes or nanowires are desirable in order to be able to understand the pure electrical properties of conducting polymer nanostructures. Compared with bulk conducting polymers, conducting polymer nanostructures are expected to display improved performance in technological applications because of the unique properties arising from their nanometer-scaled size: high conductivity, large surface area, and light weight. Thus, it is also desirable to develop promising applications for conducting polymer nanostructures. In accordance with the issues described above, our research focuses on a new synthesis method to form conducting polymer nanostructures and on the related formation mechanism of the resultant nanostructures. The electrical and transport properties of single nanotubes of conducting polymer, measured by a four-probe method, and promising applications of such template-free-synthesized conducting polymer nanostructures as new microwave absorbing materials and sensors guided by a reversible wettability are also of interest. This article reports some of our main results and reviews some important contributions of others.

Highly Disordered Polymer Field Effect Transistors: N-Alkyl Dithieno[3,2-b:2′,3′-d]pyrrole-Based Copolymers with Surprisingly High Charge Carrier Mobilities

Abstract: A series of novel electroactive and photoactive conjugated copolymers based on N-alkyl dithieno[3,2-b:2′,3′-d]pyrroles (DTP) and thiophene (TH) units (DTP-co-THs) were synthesized using a Stille coupling reaction and exhibited molecular weights of 1.6 × 104 to 5.0 × 104 g/mol. The incorporation of soluble substituted thiophenes and planar DTP units resulted in low band gap, highly conductive polymers. DTP-co-THs exhibited excellent solubility in common organic solvents and formed high-quality films. Optical characterization revealed that the band gaps of DTP-co-THs were between 1.74 and 2.00 eV, lower than regioregular poly(3-alkylthiophenes). Electrochemical characterization showed that the HOMO energy levels of DTP-co-THs are between −4.68 and −4.96 eV. When doped, DTP-co-THs exhibited high conductivities up to 230 S/cm with excellent stability. The different thiophene substituent patternsʼ effect on the polymers’ optical and electronic properties was then examined by density functional theory computati...

Highly aligned ultrahigh density arrays of conducting polymer nanorods using block copolymer templates.

Abstract: Ultrahigh density arrays of conducting polypyrrole (PPy) nanorods are fabricated directly on the indium-tin oxide coated glass by an electropolymerization within a porous diblock copolymer template. The nanorods are shown to have conductivity much higher than thin PPy films, due to the high degree of chain orientation, even though the separation distance for two neighboring PPy main chains is as small as 0.37 nm. The ultrahigh density arrays of conducting polymer nanorods have potential applications as sensor materials, nanoactuators, and organic photovoltaic devices.

Control of the nanoscale crystallinity and phase separation in polymer solar cells

Abstract: Grazing-incidence x-ray diffraction and atomic force microscopy were performed on bulk heterojunction regioregular poly(3-hexylthiophene) (RR-P3HT) [6,6]-phenyl-C71-butyric acid methyl esters spin-cast films with different film processing conditions to correlate the crystalline nanostructure of P3HT with the corresponding solar cell performance. The increase in long wavelength absorption for solvent annealed films is related to highly conjugated crystal structure of RR-P3HT phase-separated in the active layer. Upon thermal annealing, the solvent annealed 50-nm-thick device shows high solar cell performance with fill factor up to 73% and power conversion efficiency of 3.80%.

Nanowire Conductive Polymer Gas Sensor Patterned Using Self-Assembled Block Copolymer Lithography

Abstract: Nanostructured conjugated organic thin films are essential building blocks for highly integrated organic devices. We demonstrate the large-area fabrication of an array of well-ordered 15 nm wide conducting polymer nanowires by using an etch mask consisting of self-assembled patterns of cylinder-forming poly(styrene-b-dimethylsiloxane) diblock copolymer confined in topographic templates. The poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) nanowires operated as an ethanol vapor sensor, suggesting that the electronic properties of the organic film were preserved during the patterning processes. The higher sensitivity to ethanol vapor, compared to an unpatterned film with the same thickness, was attributed to the enhanced surface-to-volume ratio of the nanowire array.

Significantly reducing electrical resistivity by forming conductive Ni chains in a polyurethane shape-memory polymer/carbon-black composite

Abstract: We demonstrate an approach to significantly reduce the electrical resistivity in a polyurethane shape-memory polymer (SMP) filled with randomly distributed carbon black (CB). With an additional small amount of randomly distributed Ni microparticles (0.5vol%) in the SMP/CB composite, its electrical resistivity is only reduced slightly. However, if these Ni particles are aligned into chains (by applying a low magnetic field on the SMP/CB/Ni solution before curing), the drop of the electrical resistivity is significant. This approach, although demonstrated in a SMP, is applicable to other conductive polymers.

Application of chemically synthesized conducting polymer-polypyrrole as a carbon dioxide gas sensor

Abstract: A polypyrrole (PPy) has been a subject of many studies because it exhibits relatively high electrical conductivity, good environmental stability and versatility of synthesis. Pyrrole (Py), the monomer of PPy, has been polymerized via chemically oxidative polymerization in the presence of an oxidant (FeCl 3 ). Two samples of PPy in the form of odorless black powder were prepared by taking the weight ratios of Py to FeCl 3 of 0.429 (low) and 4.290 (high). At both ratios, the concentration of oxidant was kept constant. PPy-I sensor using PPy powder of a Py/FeCl 3 weight ratio of 0.429 and PPy-II sensor using PPy powder of a Py/FeCl 3 weight ratio of 4.290 were prepared by screen-printing technique on a glass substrate. For electrical contacts, electrodes of conducting silver paint were printed on adjacent sides of the sensor film. PPy-I and PPy-II sensors were used for CO 2 gas sensing investigation. Sensitivity of sensors at different concentrations of CO 2 gas was measured by a voltage drop method at room temperature (303 K). At certain higher concentration of CO 2 gas, a saturation effect was observed with both sensors. The response and recovery time were found short in PPy-II sensor. XRD, SEM, FTIR and TG/DTA were used to analyze the PPy powder. In the π-orbital overlap of neighboring molecules of the PPy structure, the π-electrons delocalize along the entire chain, which provides semiconducting and conducting properties. CO 2 molecules formed weak bonds with π-electrons of PPy. This causes an increase of resistance of the material in the presence of CO 2 gas.