Conductivity Of Organic Materials Research Articles

Field-induced crossover from phonon to field assisted hopping conductivity in organic materials

Recently the change in temperature dependence of conductivity observed in polythiophene field-effect transistors has been attributed to field-induced metal-insulator transition. Under a high source-drain voltage, the conductivity becomes independent from temperature and depends exponentially on the inverse of the square root of electric field. In this paper we present a theoretical interpretation of this behavior in the framework of hopping mechanism. The ingredient of this model, is the energy gained from the electrical field is always larger than the energy difference between the localized states involved into the charge transitions, which induces a crossover from phonon-assisted hopping to field-assisted hopping.

Increase in Discharge Capacity of Li Battery Assembled with Electrochemically Prepared V2O5/polypyrrole-composite-film Cathode

materials. In addi-tion to the high surface to volume ratio, the specific capacities can be increased by enhancing the Li accessibility or by in-creasing the conductivity of the electrode materials. The kinetic barriers induced by the limited Li ion accessibility within ca-thodes can be minimized by embedding inorganic electrode ma-terials in conductive organic materials. Conductive polymers are attractive electrode materials owing to their electrochemical activities;

Charge Separation at Molecular Donor–Acceptor Interfaces: Correlation Between Morphology and Solar Cell Performance

Blends of organic electron and hole conductive materials are widely used for ambipolar charge-carrier transport and donor/acceptor (DA) photovoltaic cells. Thereby, the efficiency of these excitonic solar cells is correlated to the morphology of the interface between the donor and the acceptor materials, which in turns depends on the preparation conditions, the crystallization of the particular materials, and the interaction between the donor and acceptor molecules. In this contribution, the influence of the morphology on the solar cell architecture and performance will be discussed using different molecular DA combinations.

Electroconductive paper prepared by coating with blends of poly(3,4‐ethylenedioxythiophene)/poly(4‐styrenesulfonate) and organic solvents

AbstractElectroconductive papers were produced by coating commercial base papers with blends of poly(3,4‐ethylenedioxythiophene)/poly(4‐styrenesulfonate) (PEDOT:PSS) and organic solvents. The bulk conductivities of the coated papers were measured using a four‐probe technique. One‐sided and two‐sided coating gave comparable conductivity levels. The presence of sorbitol and isopropanol in the PEDOT:PSS blends did not enhance the bulk conductivity of the coated paper, and with increasing concentrations of these solvents, the conductivity decreased due to dilution of the conducting component. Samples coated with PEDOT:PSS blends containing N‐methylpyrrolidone (NMP) or dimethyl sulfoxide (DMSO) exhibited a higher conductivity than those coated with pure PEDOT:PSS because of their plasticizing effect and conformational changes of PEDOT molecules indicated by the red shift and disappearance of the shoulder peak at about 1442 cm−1 in the Raman spectra of the coated samples. EDS imaging showed that PEDOT:PSS is distributed throughout the thickness direction of the paper. Contact angle measurements were made to monitor the hydrophilicity of the paper surface and total sulfur analysis was used to determine the amount of PEDOT:PSS deposited onto the paper. The tensile strength of all the paper samples increased slightly after treatment. Thus, it is demonstrated that enhanced bulk conductivity in the order of 10−3 S/cm can be achieved by using organic conductive materials and surface treatment techniques. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Mixed crystalline films of co-evaporated hydrogen- and fluorine-terminated phthalocyanines and their application in photovoltaic devices

Blends of organic electron and hole conductive materials are widely used for ambipolar charge carrier transport and photovoltaic cells. An obvious choice for donor–acceptor blends are organic semiconducting materials in their hydrogenated and fluorinated form, since they combine potentially suitable electronic properties with structural compatibility of the two constituents. This study focuses on the structural, optical, and electrical properties of blends using hydrogenated copper-phthalocyanine ( H 16 CuPc ) in combination with its per-fluorinated version ( F 16 CuPc ) . Using X-ray scattering, scanning force microscopy and optical absorption measurements we show that mixed crystalline films are obtained by co-evaporation of the two materials. Electrical transport measurements reveal a profound reduction of the current for bipolar charge injection in mixed films. We discuss the formation of self-trapped charge transfer excitons as possible explanation for this unexpected behaviour, which impedes the usability of this system in photovoltaic cells.

Organic against inorganic electrodes grown onto polymer substrates for flexible organic electronics applications

One of the most challenging topics in the area of organic electronic devices is the growth of transparent electrodes onto flexible polymeric substrates that will be characterized by enhanced conductivity in combination with high optical transparency. An essential aspect for these materials is their synthesis and/or microstructure which define the transparency, the stability and the interfacial chemistry which in turn determine the performance and stability of the organic electronic devices, such as organic light emitting diodes, organic photovoltaics, etc. In this work, we will discuss the latest advances in the growth of organic (e.g. PEDOT:PSS) and inorganic (e.g. zinc oxide–ZnO, indium tin oxide–ITO) conductive materials and their deposition onto flexible polymeric substrates. We will compare the optical, structural, nano-mechanical and nano-topographical properties of the inorganic and organic materials and we investigate the effect of their structure on their properties and functionality. In the case of the organic conductive materials, we will discuss the effects of PEDOT:PSS weight ratios and the various spin speeds on their optical and electrical properties. Furthermore, in the case of ZnO the growth mechanisms, interface phenomena, crystallinity and optical properties of ZnO thin films grown onto polymer and hybrid (inorganic–organic) flexible substrates will be also discussed.

Reagentless Electrochemical Hydrogen Peroxide Biosensor Based on Toluidine Blue-Derived Organic Material and Functionalized Gold Nanoparticles

In this paper, a biosensor was proposed. At first, an organic conductive material, 3,4,9,10-perylenetetracarboxylic acid-toluidine blue (PTATB), was synthesized by 3,4,9,10-perylenetetracarboxylic dianhydride and toluidine blue. Then the prepared PTATB was dispersed into solution and dropped on a glassy carbon electrode to form a stable composite film with efficient redox activity. Later, gold nanoparticles (GNPs) were carbonylated by -carboxymethyl chitosan (CMCS) to obtain functionalized gold nanoparticles (CMCS-GNPs), which were adsorbed on the film with positive charge via electrostatic interaction. Finally, hemoglobin, as a model enzyme, was covalently immobilized onto the electrode modified with matrix to construct a new biosensor. The proposed biosensor displays a high sensitivity, fast analytical time, and broader linear response to in the range from to with a limit of detection of at 3 times the background noise. The apparent Michaelis–Menten constant and the maximum current density for the proposed biosensor were estimated to be 0.62 mM and , respectively. This work provided a new avenue for the electrochemical investigation of enzyme immobilization.

A percolation approach to the temperature and charge carrier concentration dependence of the hopping conductivity in organic materials

AbstractUsing the bond criterion, different hopping conduction regimes in organic conductors described by a Gaussian density of states are analyzed in different regions of the (n, T) plane. The crossover conditions between different regimes are considered with regard to the temperature and concentration dependences of the characteristic energies (the transport energy and Fermi level). The meaning of the concentration dependence of the apparent mobility outside the weak‐concentration region is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Molecular implantation using a laser-induced molecular micro-jet

Implantation of organic molecules into conductive organic or inorganic materials on the nanometre scale is one of the challenging problems in materials research that has to be solved. We have developed an advanced method of laser implantation suitable for producing organic molecular dots with sizes of a few hundred nanometres on organic and inorganic solid materials. This method involves transferring of organic molecules from a source film to a target material through a water-filled space-gap using a laser-induced molecular micro-jet. In this way, organic dots of Coumarin 6 (C6) molecules were successfully implanted into different target materials such as polymer, glass, copper, indium tin oxide (ITO), stainless steel, and so on. The shapes of the implanted dots as well as the shapes of the holes, caused by damage to the source or target films during laser irradiation, depended on whether water or air filled the space-gap between the films.

Effect of Hydroxyl Group on the Characteristics of Solution Processed n- and p-type OFETs using Poly(p-silsesquioxane) Derivatives as a Gate Insulator

AbstractOrganic field effect transistors (OFETs) fabricated on the polymer substrate including conductive organic materials and polymeric gate insulator is one of promising devices for the flexible electronic devices. For OFETs with a conductive organic layer formed on the gate insulating materials, the performance of devices strongly depends on the molecular structure of the gate insulators. In this study, we investigated the effect of hydroxyl group of gate insulating materials on the characteristics of n- and p-type OFETs utilizing [6,6]-phenyl C61-butyric acid methyl ester (PCBM), α, ω-dihexylsexithiophene (DH6T) and pentacene OFETs as a conducting layer, respectively. Poly(p-silsesquioxane) (PSQ) derivatives are used as a polymeric gate insulator, which containes various ratios of phenol-group with a hydroxyl group bonded to a phenyl ring in the side chain of their molecular structures.

Organic Conducting Materials, in Particular Polythiophenes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and New Reaction of Sulfur‐Containing Heterocycles for Studies of Organic Conducting Materials

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structure and electronic properties of cyanothiophene derivatives: A theoretical ab initio and DFT study*

AbstractOligotiophenes derivatives present potential applicability for the construction of electronic devices. In this work we analyzed the structure–property relationship for a class of cyanothiophene compounds using ab initio [Hartree–Fock (HF) and second‐order Møller–Plesset (MP2)] and density functional theory (DFT) theoretical approaches. The energy gap between the valence and conduction bands was evaluated using distinct methodologies, being the results compared with experimental data. At the DFT level using the HF optimized geometries (DFT//HF) the average deviation was 0.22 eV (SVWN//HF) and 0.23 eV (BLYP//HF). The results from the configuration interaction implemented in the semiempirical ZINDO/S‐CI program were also in good agreement with experiment, being the average deviation found to be 0.20 eV when the HF optimized geometries were used. In general, the energy gap for the cyanothiophene derivatives was lower than the values for the unsubstituted parent compounds, showing that these molecules should be considered as a good prototype to develop new organic conductor polymers. We believe this study may be useful to predict electronic properties that are related with the conductivity of organic materials. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

First stable tetracyanodiphenoquinodimethane with a completely planar geometry: Preparation, X-ray structure, and highly conductive complexes of bis[1,2,5]thiadiazolo-TCNDQ

The titled tetracyanodiphenoquinodimethane (TCNDQ) derivative was newly designed and prepared as a novel component for highly conductive organic materials. Introduction of 1,2,5-thiadiazole rings into the TCNDQ skeleton leads to large stabilization in the neutral state. X-ray analysis has revealed their structural details which suggest that interatomic interactions (CH…N, S…N) play an important role in determining the molecular and crystal structure. The novel electron acceptor shows strong electron affinity comparable with that of TCNQ, and gave highly conductive charge-transfer (CT) complexes and an anion radical salt.

ChemInform Abstract: New Precursors for Preparing Organic Conducting Materials: Synthesis of (R)‐Hydroxymethylbis(ethylenedithio)tetrathiafulvalene, and the Ring Expansion of a Cyclic Sulfate Ester.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

3,4-polyethylenedioxythiophene (PEDT): Conductive coatings technical applications and properties

Intensive development work on organic conductors has been carried out world wide. It is only recently that the problem of how to process these conductive materials has been solved. This technology breakthrough led to the first practical applications. Organic conductive material development is briefly reviewed. The PEDT polymer properties of conductivity, stability and processability are described. PEDT's synthesis and the importance of its processability leading to the first practical applications in antistatic use, capacitor design, and printed circuit board are discussed.

Montmorillonite K10/ZnCl2 Catalyzed Alkyl Disulfide Substitution Reactions: Preparation of Thiomethyl Derivatives for the Synthesis of Organic Conducting Materials

Montmorillonite K10/ZnCl2 Catalyzed Alkyl Disulfide Substitution Reactions: Preparation of Thiomethyl Derivatives for the Synthesis of Organic Conducting Materials

Montmorillonite K10/ZnCl2 Catalyzed Alkyl Disulfide Substitution Reactions: Preparation of Thiomethyl Derivatives for the Synthesis of Organic Conducting Materials

Experiments are described detailing a method for the direct introduction of thiomethyl groups into activated benzenes, thiophene and benzo[b]thiophene using an activated mesoporous clay to promote thiomethyl substitution. Elaboration of 2,3-dithiomethylbenzo[b]thiophene, a product of the clay-catalyzed reaction of benzo[b]thiophene with dimethyl disulfide, to a tetrathiafulvalene derivative is described.

Synthesis and structure of molecules containing linked donor and acceptor units, new tellurium-TTF derivatives and their charge transfer complexes

Our efforts in designing, synthesizing and characterizing organic conducting materials have been focused primarily on the preparation and structure determination of D-A-D (D = donor, A = acceptor) and A-D-A molecular units in which donors and acceptors are chemically attached via bridging atoms or groups. The strategy that motivates the synthetic work is aimed at gaining control over the architectural features of the solid state structures of the materials, since gaining control over the three-dimensional structure is a vital pre-condition for achieving electrical conductivity in organic materials. Construction of such molecular units predetermines the D-A molar ratio as well as the maximum degree of charge transfer. Moreover, we have already shown that this molecular motif has a high propensity to crystallize in the desired crystallographic arrangement, characterized by segregated stacks of both donors and/or acceptor, with significant overlap between adjacent units in the stack. Following this approach we have synthesized two types of molecules; one contains two donors attached to one acceptor via -CH 2- or S atom bridges, and in the other, two acceptors are linked to one donor via methylene bridges. In addition, the importance of introducing heavy atoms in charge-transfer complexes has long been recognized. Consequently, extensive work has been carried out on the synthesis of various TTF derivatives, in which Se and Te atoms replace sulfur or hydrogen atoms in TTF. Recently, we have synthesized new compounds in which two TTF molecules are linked via tellurium atoms, TTF-Te-TTF and TTF-Te-Te-TTF, and prepared their complexes with TCNQ. They all exhibit conductivity at r.t.

Benzene Bis(diazocyanides)—the First Acceptors of the Inverse Wurster Type for Conductive Organic Materials

Benzene Bis(diazocyanides)—the First Acceptors of the Inverse Wurster Type for Conductive Organic Materials