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Charge Transport (charge + transport)
Terms modified by Charge Transport Selected AbstractsThe Impact of Polymer Regioregularity on Charge Transport and Efficiency of P3HT:PCBM Photovoltaic DevicesADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Ralf Mauer Abstract The charge transport in pristine poly(3-hexylthiophene) (P3HT) films and in photovoltaic blends of P3HT with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is investigated to study the influence of charge-carrier transport on photovoltaic efficiency. The field- and temperature dependence of the charge-carrier mobility in P3HT of three different regioregularities, namely, regiorandom, regioregular with medium regioregularity, and regioregular with very high regioregularity are investigated by the time-of-flight technique. While medium and very high regioregularity polymers show the typical absorption features of ordered lamellar structures of P3HT in the solid state even without previous annealing, films of regiorandom P3HT are very disordered as indicated by their broad and featureless absorption. This structural difference in the solid state coincides with partially non-dispersive transport and hole mobilities µh of around 10,4 and 10,5,cm2 V,1 s,1 for the high and medium regioregularity P3HT, respectively, and a slow and dispersive charge transport for the regiorandom P3HT. Upon blending the regioregular polymers with PCBM, the hole mobilities are typically reduced by one order of magnitude, but they do not significantly change upon additional post-spincasting annealing. Only in the case of P3HT with high regioregularity are the electron mobilities similar to the hole mobilities and the charge transport is, thus, balanced. Nonetheless, devices prepared from both materials exhibit similar power conversion efficiencies of 2.5%, indicating that very high regioregularity may not substantially improve order and charge-carrier transport in P3HT:PCBM and does not lead to significant improvements in the power-conversion efficiency of photovoltaic devices. [source] Thermo-Switchable Charge Transport and Electrocatalysis Using Metal-Ion-Modified pNIPAM-Functionalized ElectrodesADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Michael Riskin Abstract Metal ions (Ag+, Cu2+, Hg2+) are incorporated into an electropolymerized, poly(N -isopropyl acrylamide), pNIPAM, thermosensitive polymer associated with an electrode using the "breathing-in" method. The ion-functionalized pNIPAM matrices reveal ion-dependent gel-to-solid phase-transition temperatures (28,±,1,°C, 25,±,1,°C, 40,±,1,°C for the Ag+, Cu2+, and Hg2+ -modified pNIPAM, respectively). Furthermore, the ion-functionalized polymers exhibit quasi-reversible redox properties, and the ions are reduced to the respective Ag0, Cu0, and Hg0 nanocluster-modified polymers. The metal-nanocluster-functionalized pNIPAM matrices enhance the electron transfer (they exhibit lower electron-transfer resistances) in the compacted states. The electron-transfer resistances of the metal-nanocluster-modified pNIPAM can be cycled between low and high values by temperature-induced switching of the polymer between its contracted solid and expanded gel states, respectively. The enhanced electron-transfer properties of the metal nanocluster-functionalized polymer are attributed to the contacting of the metal nanoclusters in the contracted state of the polymers. This temperature-switchable electron transfer across a Ag0 -modified pNIPAM was implemented to design a thermo-switchable electrocatalytic process (the temperature-switchable electrocatalyzed reduction of H2O2 by Ag0 -pNIPAM). [source] Controllable Molecular Doping and Charge Transport in Solution-Processed Polymer Semiconducting LayersADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Yuan Zhang Abstract Here, controlled p-type doping of poly(2-methoxy-5-(2,-ethylhexyloxy)- p -phenylene vinylene) (MEH-PPV) deposited from solution using tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) as a dopant is presented. By using a co-solvent, aggregation in solution can be prevented and doped films can be deposited. Upon doping the current,voltage characteristics of MEH-PPV-based hole-only devices are increased by several orders of magnitude and a clear Ohmic behavior is observed at low bias. Taking the density dependence of the hole mobility into account the free hole concentration due to doping can be derived. It is found that a molar doping ratio of 1 F4-TCNQ dopant per 600 repeat units of MEH-PPV leads to a free carrier density of 4,×,1022,m,3. Neglecting the density-dependent mobility would lead to an overestimation of the free hole density by an order of magnitude. The free hole densities are further confirmed by impedance measurements on Schottky diodes based on F4-TCNQ doped MEH-PPV and a silver electrode. [source] Control of Charge Transport in Iridium(III) Complex-Cored Carbazole Dendrimers by Generation and Structural ModificationADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Salvatore Gambino Abstract Here, the charge transporting properties of a family of highly phosphorescent iridium(III) complex-cored carbazole dendrimers designed to have improved charge transport by incorporating carbazole units into the dendrons are studied. Firstly, the effect of the dendrimer generation and the role of dendron for materials with one dendron per ligand of the core are considered. It is shown, in contrast to previously reported light-emitting dendrimers, that in this case the carbazolyl-based dendrons have an active role in charge transport. Next, the effect on the charge transport of attaching two dendrons per ligand to the dendrimer core is explored. In this latter case, for the so called "double dendron" material a highly non-dispersive charge transport behavior is observed, together with a time-of-flight mobility of the order of 10,3,cm2 V,1,s,1. Furthermore the lowest energetic disorder parameter (,) ever reported for a solution-processed conjugated organic material is found, ,,< ,20 meV. [source] High Mobility Ambipolar Charge Transport in Polyselenophene Conjugated PolymersADVANCED MATERIALS, Issue 21 2010Zhuoying Chen High mobility ambipolor polymer field-effect transistors based on a series of regioregular polyselenophenes are presented together with their morphological and optical properties. Balanced electron and hole mobilities on the order of 0.03,cm2,V,1,s,1 are observed by employing a simple top-gate/bottom-contact configuration with photolithographically defined gold source/drain contacts. High gain complementary-like voltage inverters are demonstrated based on two identical ambipolar transistors. [source] Efficient, Stable Bulk Charge Transport in Crystalline/Crystalline Semiconductor,Insulator BlendsADVANCED MATERIALS, Issue 44 2009Avinesh Kumar Efficient and stable ambipolar charge transport in the bulk of crystalline/crystalline P3HT/HDPE systems, as evidenced by time-of-flight (TOF) photoconductivity measurements, is found. Interestingly, certain blend compositions displayed significantly enhanced bulk charge-transport properties compared to neat P3HT, with ,TOF measured for 80:20,wt% P3HT:PE blends being up to one order of magnitude higher than those found in neat P3HT. [source] Tuning Crystalline Solid-State Order and Charge Transport via Building-Block Modification of OligothiophenesADVANCED MATERIALS, Issue 36 2009Colin Reese The packing structure of a series of oligothiophenes is tuned via terminal substitution (see figure). The structural changes dramatically alter intermolecular interactions and charge-transport properties, as measured by elastomeric single-crystal field-effect transistors. Electronic structure calculations reveal the sensitivity of the transport efficiency to orbital nodal alignment, as correlated to the observed trend in field-effect mobilities. [source] Charge Transport in Disordered Organic Materials and Its Relevance to Thin-Film Devices: A Tutorial ReviewADVANCED MATERIALS, Issue 27 2009Nir Tessler Abstract Semiconducting polymers and small molecules form an extremely flexible class of amorphous materials that can be used in a wide range of applications, some of which are display, radio-frequency tags, and solar cells. The rapid progress towards functional devices is occurring despite the lack of sufficient understanding of the physical processes and very little experience in device engineering. This tutorial review aims to provide sufficient intuitive background to draw more researchers to look into the fundamental aspects of device physics and engineering. [source] Precise Structure of Pentacene Monolayers on Amorphous Silicon Oxide and Relation to Charge TransportADVANCED MATERIALS, Issue 22 2009Stefan C. B. Mannsfeld The precise molecular packing in pentacene monolayers on silicon oxide is determined for the first time using a combination of grazing incidence X-ray diffraction (GIXD) and crystallographic refinement calculations. The pentacene molecules are found to adopt a completely tilt-free herringbone motif, the charge-transport properties of which are discussed on the basis of density functional theory calculations. [source] Polymer Charge Transport: Charge-Transport Anisotropy Due to Grain Boundaries in Directionally Crystallized Thin Films of Regioregular Poly(3-hexylthiophene) (Adv. Mater.ADVANCED MATERIALS, Issue 16 200916/2009) Grain boundaries can be engineered in directionally oriented thin films of poly(3-hexylthiophene) report Alberto Salleo and co-workers on p. 1568. Charge-transport studies coupled with X-ray and AFM characterization indicate that intergrain transport is greatly facilitated when neighboring grains can be bridged by relatively straight polymer chains. [source] Advantageous 3D Ordering of ,-Conjugated Systems: A New Approach Towards Efficient Charge Transport in any Direction,ADVANCED MATERIALS, Issue 24 2007H. Pang A new organic semiconductor based on a benzobisthiazole core has been studied as a hole transport material in field effect transistors; remarkably, the material self-assembles in the solid state to give intermolecular short contacts in all three dimensions. [source] Liquid Crystalline Ordering and Charge Transport in Semiconducting MaterialsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2009Wojciech Pisula Abstract Organic semiconducting materials offer the advantage of solution processability into flexible films. In most cases, their drawback is based on their low charge carrier mobility, which is directly related to the packing of the molecules both on local (amorphous versus crystalline) and on macroscopic (grain boundaries) length scales. Liquid crystalline ordering offers the possibility of circumventing this problem. An advanced concept comprises: i) the application of materials with different liquid crystalline phases, ii) the orientation of a low viscosity high temperature phase, and, iii) the transfer of the macroscopic orientation during cooling to a highly ordered (at best, crystalline-like) phase at room temperature. At the same time, the desired orientation for the application (OLED or field-effect transistor) can be obtained. This review presents the use of molecules with discotic, calamitic and sanidic phases and discusses the sensitivity of the phases with regard to defects depending on the dimensionality of the ordered structure (columns: 1D, smectic layers and sanidic phases: 2D). It presents ways to systematically improve charge carrier mobility by proper variation of the electronic and steric (packing) structure of the constituting molecules and to reach charge carrier mobilities that are close to and comparable to amorphous silicon, with values of 0.1 to 0.7,cm2,·,V,1,·,s,1. In this context, the significance of cross-linking to stabilize the orientation and liquid crystalline behavior of inorganic/organic hybrids is also discussed. [source] Linking Polythiophene Chains Through Conjugated Bridges: A Way to Improve Charge Transport in Polymer Solar CellsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2006Erjun Zhou Abstract Summary: A series of cross-linked polythiophene derivatives (P1,4) are synthesized by adding different ratio (0, 2, 5, and 10%) of conjugated cross-linker via a Stille coupling reaction. From P1,4, with the increase of the content of the conjugated bridges, the UV-visible absorption peaks of the polymers were shifted towards blue and their electrochemical bandgap increased. The hole mobilities of P1,4 as determined from the SCLC model are 5.23,×,10,6, 1.28,×,10,4, 7.01,×,10,3, and 2.34,×,10,5 cm2,·,V,1,·,s,1, respectively. The PCEs of the polymer solar cells based on P1,4 are 0.37, 1.05, 1.26, and 0.78%, respectively. The improvement of PCE of the devices based on P2,4 compared with that of P1 may be due to the increase of hole mobility. Molecular structure of the polythiophene derivatives (P1,4). [source] Comparing Spin-Selective Charge Transport through Donor,Bridge,Acceptor Molecules with Different Oligomeric Aromatic Bridges,ANGEWANDTE CHEMIE, Issue 16 2010Der, -Wert, der die exponentielle Abstandsabhängigkeit der Singulett- und Triplett-Ladungsrekombinationswege charakterisiert, wurde für drei Donor-Brücke-Akzeptor(DBA)-Moleküle bestimmt. p -Phenylethinylen- und Fluorenon-Brücken ergaben ähnliche , -Werte, p -Phenylen-Brücken dagegen deutlich andere (siehe Bild). Somit hängt , für Singulett- wie Triplett-Ladungsrekombinationen nicht von der Brücke, sondern vom System ab. [source] Anomalous Charge Transport in CeB6.CHEMINFORM, Issue 49 2006M. I. Ignatov Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Organic Nanomaterials: Morphological Control for Charge Stabilization and Charge TransportCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2009P. Pramod Dr. Abstract How grows it? Organic nanostructured materials have been projected as active components in optoelectronic devices. Recent efforts in manipulating the morphology of organic nanomaterials, particularly on their size and shape, are summarized in this Focus Review. Potential application of organic nanostructured materials in charge stabilization and transporting are also discussed. Chromophoric systems with proper recognition motifs can organize into well-defined arrays forming supramolecular assemblies and further into nanoscopic materials. The optical and electrical properties of organic nanomaterials depend upon the stacking modes of organic molecules and also on the kind of interaction between different chromophore units (such as H- and J- type aggregates). These types of aggregates can dramatically alter the opto-electronic properties of organic nanostructures. Hence efforts are currently directed towards manipulating the morphology of organic nanomaterials, particularly on their size and shape by adopting different techniques and these aspects are discussed. Recent studies have shown that such nanostructures are extremely important in the development of optoelectronic systems such as photovoltaic devices. This Focus Review also discusses the potential application of organic nanomaterials in charge stabilization and transport. [source] Charge Transport in Redox Polyelectrolyte Multilayer Films: The Dramatic Effects of Outmost Layer and Solution Ionic StrengthCHEMPHYSCHEM, Issue 13 2010Dr. Mario Tagliazucchi Abstract The redox switching kinetics, that is, charge transfer and transport in layer-by-layer-deposited electroactive polyelectrolyte multilayers is systematically studied with variable-scan-rate cyclic voltammetry. The experiments are performed with films finished in the redox polycation (an osmium pyridine,bipyridine derivatized polyallylamine, PAH-Os) and the polyanion (polyvinyl sulfonate, PVS), in solutions of different electrolyte concentrations. A modified diffusion model is developed to account for the experimentally observed dependence of the average peak potential with the scan rate. This model is able to describe both the redox peak potential and the current, providing information on the electron-transfer rate constants and the diffusion coefficient for the electron-hopping mechanism. While the former does not vary with the ionic strength or the nature of the outmost layer, polyanion-capped films present an electron-hopping diffusion coefficient at low ionic strength that is three orders of magnitude smaller than that for PAH-Os-capped films. The effect is offset at high ionic strength. We discuss the possible causes of the effect and the important consequences for electrochemical devices built by layer-by-layer self-assembly, such as amperometric biosensors or electrochromic devices. [source] Theoretical Characterization of Charge Transport in One-Dimensional Collinear Arrays of Organic Conjugated MoleculesCHEMPHYSCHEM, Issue 5 2010Lucas Viani Abstract A great deal of interest has recently focused on host,guest systems consisting of one-dimensional collinear arrays of conjugated molecules encapsulated in the channels of organic or inorganic matrices. Such architectures allow for controlled charge and energy migration processes between the interacting guest molecules and are thus attractive in the field of organic electronics. In this context, we characterize here at a quantum-chemical level the molecular parameters governing charge transport in the hopping regime in 1D arrays built with different types of molecules. We investigate the influence of several parameters (such as the symmetry of the molecule, the presence of terminal substituents, and the molecular size) and define on that basis the molecular features required to maximize the charge carrier mobility within the channels. In particular, we demonstrate that a strong localization of the molecular orbitals in push,pull compounds is generally detrimental to the charge transport properties. [source] The Influence of Charge Transport and Recombination on the Performance of Dye-Sensitized Solar CellsCHEMPHYSCHEM, Issue 1 2009Mingkui Wang Dr. Abstract Electrochemical impedance spectroscopy (EIS) and transient voltage decay measurements are applied to compare the performance of dye sensitized solar cells (DSCs) using organic electrolytes, ionic liquids and organic-hole conductors as hole transport materials (HTM). Nano-crystalline titania films sensitized by the same heteroleptic ruthenium complex NaRu(4-carboxylic acid-4,-carboxylate) (4,4,-dinonyl-2,2,-bipyridyl)(NCS)2,, coded Z-907Na are employed as working electrodes. The influence of the nature of the HTM on the photovoltaic figures of merit, that is, the open circuit voltage, short circuit photocurrent and fill factor is evaluated. In order to derive the electron lifetime, as well as the electron diffusion coefficient and charge collection efficiency, EIS measurements are performed in the dark and under illumination corresponding to realistic photovoltaic operating conditions of these mesoscopic solar cells. A theoretical model is established to interpret the frequency response off the impedance under open circuit conditions, which is conceptually similar to photovoltage transient decay measurements. Important information on factors that govern the dynamics of electron transport within the nanocrystalline TiO2 film and charge recombination across the dye sensitized heterojunction is obtained. [source] Effect of Traps on Carrier Injection and Transport in Organic Field-effect TransistorIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2010Martin Weis Non-member Abstract This study illustrates effect of traps on the charge injection and transport in the organic field-effect transistor (OFET). Here are included silicon nanoparticles (NPs) on a semiconductor-gate insulator interface, which work as trapping centers of charge carriers. Charge transport and injection phenomena are investigated by electrical measurements in presence of traps with designed densities. We find that OFETs with a low concentration of intrinsic carriers, such as a pentacene, are extremely sensitive to the internal electric fields. A significant threshold voltage shift due to trapped charge is observed, with a possibility to tune it by controlling the NP density. We demonstrate that the NP film can serve to design the amount of the accumulated charge in OFET and thus change the space-charge-limited conditions to the injection-limited conditions. A detailed analysis of pentacene OFET based on dielectric properties and the Maxwell-Wagner model reveals the internal electric field created by NPs. Additionally, the effect of NPs is discussed with respect to effective mobility, and its decrease is related to deceleration of carrier propagation by the trapping effect as well as low injection due to the increase of the carrier injection barrier by the internal field. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Charge transport in stacking metal and metal-free phthalocyanine iodides.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2009Effects of packing, central metals, core modification, dopants, external electric field, substitutions Abstract The charge-transport properties of the one-dimensional stacking metal phthalocyanine iodides (M(Pc)I, M = Fe, Co, Ni, Cu) and metal-free phthalocyanine iodide (H2(Pc)I) have been theoretically investigated. On the basis of the tight-binding approximation and two-state theory, both the site-energy corrected energy splitting in dimer and Fock-matrix-based methods are used to calculate the transfer integral. The intermolecular motions, including interplanar translation, rotation, slip, and tilt, exert remarkable impacts on the transfer integral. The order/disorder of the dopant stack and the long-range electrostatic interactions are also demonstrated to be crucial factors for modulation of charge-transport properties. The transfer integral undergoes slight changes under an applied electric field along the stacking direction in the range of 106 , 107 V cm,1. The change of central metals in MPc has little effect on the transfer integrals, but significantly affects the reorganization energies. The extension of the ,-conjugation in macrocyclic ligand brings about considerable influence on the transfer integrals. Peripheral substitutions by animo, hydroxyl, and methyl lead to deviations from planarity of macromolecular rings, and hence affect the valence bands significantly. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Optimization of Electrochemical and Peroxide-Driven Oxidation of Styrene with Ultrathin Polyion Films Containing Cytochrome P450cam and MyoglobinCHEMBIOCHEM, Issue 1 2003Bernard Munge Abstract The catalytic and electrochemical properties of myoglobin and cytochrome P450camin films constructed with alternate polyion layers were optimized with respect to film thickness, polyion type, and pH. Electrochemical and hydrogen peroxide driven epoxidation of styrene catalyzed by the proteins was used as the test reaction. Ionic synthetic organic polymers such as poly(styrene sulfonate), as opposed to SiO2nanoparticles or DNA, supported the best catalytic and electrochemical performance. Charge transport involving the iron heme proteins was achieved over 40,320 nm depending on the polyion material and is likely to involve electron hopping facilitated by extensive interlayer mixing. However, very thin films (ca. 12,25 nm) gave the largest turnover rates for the catalytic epoxidation of styrene, and thicker films were subject to reactant transport limitations. Classical bell-shaped activity/pH profiles and turnover rates similar to those obtained in solution suggest that films grown layer-by-layer are applicable to turnover rate studies of enzymes for organic oxidations. Major advantages include enhanced enzyme stability and the tiny amount of protein required. [source] Electrical Conductance in Biological MoleculesADVANCED FUNCTIONAL MATERIALS, Issue 12 2010M. Waleed Shinwari Abstract Nucleic acids and proteins are not only biologically important polymers. They have recently been recognized as novel functional materials surpassing conventional materials in many aspects. Although Herculean efforts have been undertaken to unravel fine functioning mechanisms of the biopolymers in question, there is still much more to be done. Here the topic of biomolecular charge transport is presented with a particular focus on charge transfer/transport in DNA and protein molecules. The experimentally revealed details, as well as the presently available theories, of charge transfer/transport along these biopolymers are critically reviewed and analyzed. A summary of the active research in this field is also given, along with a number of practical recommendations. [source] Electrocatalytic Reduction and Determination of Iodate and Periodate at Silicomolybdate-Incorporated-Glutaraldehyde- Cross-Linked Poly- L -lysine Film ElectrodesELECTROANALYSIS, Issue 10 2010Yu-Ching Pan Abstract The present work describes reduction of iodate (IO3,), and periodate (IO4,) at silicomolybdate-doped-glutaraldehyde-cross-linked poly- L -lysine (PLL-GA-SiMo) film coated glassy carbon electrode in 0.1,M H2SO4. In our previous study, we were able to prepare the PLL-GA-SiMo film modified electrode by means of electrostatically trapping SiMo12O404, mediator in the cationic film of PLL-GA, and the voltammetric investigation in pure supporting indicated that the charge transport through the film was fast. Here, the electrocatalytic activity of PLL-GA-SiMo film electrode towards iodate and periodate was tested and subsequently used for analytical determination of these analytes by amperometry. The two electron reduced species of SiMo12O404, anion was responsible for the electrocatalytic reduction of IO3, at PLL-GA-SiMo film electrode while two and six electron reduced species were showed electrocatalytic activity towards IO4, reduction. Under optimized experimental conditions of amperometry, the linear concentration range and sensitivity are 2.5×10,6 to 1.1×10,2,M and 18.47,,A mM,1 for iodate, and 5×10,6 to 1.43×10,4,M and 1014.7,,A mM,1 for periodate, respectively. [source] Microdimensional Polyaniline: Fabrication and Characterization of Dynamics of Charge Propagation at Microdisk ElectrodesELECTROANALYSIS, Issue 17 2004Karolina Caban Abstract We describe fabrication of microdimensional polyanilne films in a controlled manner by voltammetric potential cycling or controlled potential electrolysis on platinum microdisk electrodes. The film grows in a form of hemispherical microdeposits, and its size largely exceeds the size of a Pt microdisk. Consequently, the film covers both the Pt substrate as well as the surrounding glass seal. Since the adhering polyaniline layer is conducting, the latter situation may lead to an increase in the effective electrode surface area. The lateral growth of polyaniline films outside the microdisk has also been demonstrated by performing diagnostic voltammetric experiments with use of a double microdisk set-up in which independent polarization of each disk is feasible. Microelectrode-based chronocoulometry, that involves an uncomplicated well-defined reduction potential step starting from the emeraldine (conducting) form and ending at leucoemeraldine (nonconducting) form, yields (upon application of a sufficiently short pulse) a well-defined linear response of charge versus square root of time that is consistent with the linear effective diffusion as the predominant charge propagation mechanism. When describing the system kinetics in terms of the effective (apparent) diffusion coefficient, we expect this parameter to be on the level of 10,8,cm2 s,1 or lower. The relative changes in dynamics of charge transport are discussed with respect to the polyaniline film loading, the size of microdisk electrode, expansion of the active electrode area, and the choice of electrolyte (strong acid) anion. The results are consistent with the view that when Pt microelectrode is modified with PANI deposit exceeding the size of the microdisk substrate, it behaves in a way as if its surface area is effectively much larger than the geometric area of Pt microdisk. [source] Synthesis and Characterization of Semiconductive Dichloridobis(thianthrene)gold(1+) Tetrachloridoaurate(1,)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2009Rachmat Triandi Tjahjanto Abstract A new (thianthrene)gold(III) complex has been synthesized in liquid SO2 as the solvent from thianthrene (TA) andAuCl3. [AuCl2(TA)2][AuCl4] [triclinic, P, a = 9.9832(2) Å, b = 10.3404(2) Å, c = 15.0798(4) Å, , = 75.038(1)°, , = 81.610(1)°, , = 68.409(1)°, V = 1396.15(5) Å3, Z = 2] has a salt-like structure consisting of [AuCl2(TA)2]+ and [AuCl4], ions, both with square-planar coordinated gold atoms of oxidation state +3. In the cation, two bent TA molecules are coordinated to Au each through one sulfur atom. The title compound is thermally stable up to 425 K and is semiconducting with a conductivity reaching 25 mSm,1 at 380 K and a low activation energy of 0.43 eV. A model for the charge transport along the stacked cationic complexes is discussed. When dissolved in chloroform [AuCl2(TA)2][AuCl4] is converted into the already known uncharged, mononuclear complex [AuCl3(TA)], which shows that a polymerization isomerism exists between the two forms.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Planarization of Polymeric Field-Effect Transistors: Improvement of Nanomorphology and Enhancement of Electrical PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Kumar A. Singh Abstract The planarization of bottom-contact organic field-effect transistors (OFETs) resulting in dramatic improvement in the nanomorphology and an associated enhancement in charge injection and transport is reported. Planar OFETs based on regioregular poly(3-hexylthiophene) (rr-P3HT) are fabricated wherein the Au bottom-contacts are recessed completely in the gate-dielectric. Normal OFETs having a conventional bottom-contact configuration with 50-nm-high contacts are used for comparison purpose. A modified solvent-assisted drop-casting process is utilized to form extremely thin rr-P3HT films. This process is critical for direct visualization of the effect of planarization on the polymer morphology. Atomic force micrographs (AFM) show that in a normal OFET the step between the surface of the contacts and the gate dielectric disrupts the self-assembly of the rr-P3HT film, resulting in poor morphology at the contact edges. The planarization of contacts results in notable improvement of the nanomorphology of rr-P3HT, resulting in lower resistance to charge injection. However, an improvement in field-effect mobility is observed only at short channel lengths. AFM shows the presence of well-ordered nanofibrils extending over short channel lengths. At longer channel lengths the presence of grain boundaries significantly minimizes the effect of improvement in contact geometry as the charge transport becomes channel-limited. [source] Temperature-Resolved Local and Macroscopic Charge Carrier Transport in Thin P3HT Layers,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Patrick Pingel Abstract Previous investigations of the field-effect mobility in poly(3-hexylthiophene) (P3HT) layers revealed a strong dependence on molecular weight (MW), which was shown to be closely related to layer morphology. Here, charge carrier mobilities of two P3HT MW fractions (medium-MW: Mn,=,7,200 g mol,1; high-MW: Mn,=,27,000 g mol,1) are probed as a function of temperature at a local and a macroscopic length scale, using pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) and organic field-effect transistor measurements, respectively. In contrast to the macroscopic transport properties, the local intra-grain mobility depends only weakly on MW (being in the order of 10,2 cm2 V,1 s,1) and being thermally activated below the melting temperature for both fractions. The striking differences of charge transport at both length scales are related to the heterogeneity of the layer morphology. The quantitative analysis of temperature-dependent UV/Vis absorption spectra according to a model of F. C. Spano reveals that a substantial amount of disordered material is present in these P3HT layers. Moreover, the analysis predicts that aggregates in medium-MW P3HT undergo a "pre-melting" significantly below the actual melting temperature. The results suggest that macroscopic charge transport in samples of short-chain P3HT is strongly inhibited by the presence of disordered domains, while in high-MW P3HT the low-mobility disordered zones are bridged via inter-crystalline molecular connections. [source] The Impact of Polymer Regioregularity on Charge Transport and Efficiency of P3HT:PCBM Photovoltaic DevicesADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Ralf Mauer Abstract The charge transport in pristine poly(3-hexylthiophene) (P3HT) films and in photovoltaic blends of P3HT with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is investigated to study the influence of charge-carrier transport on photovoltaic efficiency. The field- and temperature dependence of the charge-carrier mobility in P3HT of three different regioregularities, namely, regiorandom, regioregular with medium regioregularity, and regioregular with very high regioregularity are investigated by the time-of-flight technique. While medium and very high regioregularity polymers show the typical absorption features of ordered lamellar structures of P3HT in the solid state even without previous annealing, films of regiorandom P3HT are very disordered as indicated by their broad and featureless absorption. This structural difference in the solid state coincides with partially non-dispersive transport and hole mobilities µh of around 10,4 and 10,5,cm2 V,1 s,1 for the high and medium regioregularity P3HT, respectively, and a slow and dispersive charge transport for the regiorandom P3HT. Upon blending the regioregular polymers with PCBM, the hole mobilities are typically reduced by one order of magnitude, but they do not significantly change upon additional post-spincasting annealing. Only in the case of P3HT with high regioregularity are the electron mobilities similar to the hole mobilities and the charge transport is, thus, balanced. Nonetheless, devices prepared from both materials exhibit similar power conversion efficiencies of 2.5%, indicating that very high regioregularity may not substantially improve order and charge-carrier transport in P3HT:PCBM and does not lead to significant improvements in the power-conversion efficiency of photovoltaic devices. [source] Electronic Contact Deposition onto Organic Molecular Monolayers: Can We Detect Metal Penetration?ADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Hagay Shpaisman Abstract Using a semiconductor as the substrate to a molecular organic layer, penetration of metal contacts can be clearly identified by the study of electronic charge transport through the layer. A series of monolayers of saturated hydrocarbon molecules with varying lengths is assembled on Si or GaAs and the junctions resulting after further electronic contact is made by liquid Hg, indirect metal evaporation, and a "ready-made" metal pad are measured. In contrast to tunneling characteristics, which are ambiguous regarding contact penetration, the semiconductor surface barrier is very sensitive to any direct contact with a metal. With the organic monolayer intact, a metal,insulator,semiconductor (MIS) structure results. If metal penetrated the monolayer, the junction behaves as a metal,semiconductor (MS) structure. By comparing a molecule-free interface (MS junction) with a molecularly modified one (presumably MIS), possible metal penetration is identified. The major indicators are the semiconductor electronic transport barrier height, extracted from the junction transport characteristics, and the photovoltage. The approach does not require a series of different monolayers and data analysis is quite straightforward, helping to identify non-invasive ways to make electronic contact to soft matter. [source] | |||||||||||||||||||||||||||||||