Charge Transport Properties Of Poly Research Articles

Effect of synthesis temperature on the charge transport properties of poly(3-methylthiophene) devices

Low temperature-dependent I-V measurement was adopted to investigate an insight into the effect of synthesis temperature on the field and temperature-dependent charge transport properties of electrochemically polymerized poly(3-methylthiophene) devices. Devices having different doping levels were fabricated at two different temperatures, one at room temperature (25oC) and another at a lower temperature (5oC). The transport mechanism in the devices were studied in the temperature range 40 K to 300 K. Our studies revealed that trap controlled space charge limited conduction (TCSCLC) mechanism dominated the transport mechanism at higher temperature(T>200K) and changed to field dependent mobility model at lower temperature(T<200K). It was observed that the synthesis temperature influenced the transport parameters. Devices prepared at low temperature showed an increase in resistivity and a corresponding decrease in the charge carrier mobility compared to those prepared at high temperature. Moreover, the distribution of the trap states in the devices was also affected by the synthesis temperature, with devices fabricated at low temperature exhibiting a wider trap state distribution.

Effects of Solvent Vapor Annealing on Morphology and Charge Transport of Poly(3-hexylthiophene) (P3HT) Films Incorporated with Preformed P3HT Nanowires.

We systematically studied the influence of solvent vapor annealing on the molecular ordering, morphologies, and charge transport properties of poly(3-hexylthiophene) (P3HT) thin films embedded with preformed crystalline P3HT nanowires (NWs). Solvent vapor annealing (SVA) with chloroform (CF) was found to profoundly impact on the structural and morphological changes, and thus on the charge transport characteristics, of the P3HT-NW-embedded P3HT films. With increased annealing time, the density of crystalline P3HT NWs was increased within the resultant films, and also intra- and intermolecular interactions of the corresponding films were significantly improved. As a result, the P3HT-NW-embedded P3HT films annealed with CF vapor for 20 min resulted in a maximized charge carrier mobility of ~0.102 cm2 V−1 s−1, which is higher than that of pristine P3HT films by 4.4-fold (μ = ~0.023 cm2 V−1 s−1).

Solubility dependent trap density in poly (3-hexylthiophene) organic Schottky diodes at room temperature

The performance of organic electronic devices strongly depends on nanoscale structure/macroscopic morphology of organic semiconducting material. In this paper, we have examined the solubility dependent crystallinity and electrical charge transport properties of poly (3-hexylthiophene) (P3HT). We have used three different solvents, toluene (TLN), chloroform (CF) and dichloromethane (DCM) to dissolve the same amount of P3HT. We observed significant change in structure, morphology and optical properties of P3HT in these solvents. We obtained highly crystalline and oriented film morphology of P3HT in ultrasonicated DCM solution. Structure and morphology of films have been studied using grazing incidence X –ray diffraction (GIXD) and atomic force microscopy (AFM). The electrical charge transport properties of the films casted using TLN, CF and ultrasonicated DCM have been investigated with Schottky diode configuration ITO/P3HT/Al. The current density – voltage (J–V) characteristics are used for extracting the device parameters. The solubility driven trap density is also calculated by J–V characteristics at room temperature. We observed that highly crystalline P3HT in case of DCM has one order of magnitude less traps than P3HT (CF).

Solvent Additive-Assisted Anisotropic Assembly and Enhanced Charge Transport of π-Conjugated Polymer Thin Films.

Charge transport in π-conjugated polymer films involves π-π interactions within or between polymer chains. Here, we demonstrate a facile solution processing strategy that provides enhanced intra- and interchain π-π interactions of the resultant polymer films using a good solvent additive with low volatility. These increased interactions result in enhanced charge transport properties. The effect of the good solvent additive on the intra- and intermolecular interactions, morphologies, and charge transport properties of poly(3-hexylthiophene) (P3HT) films is systematically investigated. We found that the good solvent additive facilitates the self-assembly of P3HT chains into crystalline fibrillar nanostructures by extending the solvent drying time during thin-film formation. As compared to the prior approach using a nonsolvent additive with low volatility, the solvent blend system containing a good solvent additive results in enhanced charge transport in P3HT organic field-effect transistor (OFET) devices [from ca. 1.7 × 10-2 to ca. 8.2 × 10-2 cm2 V-1 s-1 for dichlorobenzene (DCB) versus 4.4 × 10-2 cm2 V-1 s-1 for acetonitrile]. The mobility appears to be maximized over a broad spectrum of additive concentrations (1-7 vol %), indicative of a wide processing window. Detailed analysis results regarding the charge injection and transport characteristics of the OFET devices reveal that a high-boiling-point solvent additive decreases both the contact resistance ( Rc) and channel resistance ( Rch), contributing to the mobility enhancement of the devices. Finally, the platform presented here is proven to be applicable to alternative good solvent additives with low volatility, such as chlorobenzene (CB) and trichlorobenzene (TCB). Specifically, the mobility enhancement of the resultant P3HT films increases in the order CB (bp 131 °C) < DCB (bp 180 °C) < TCB (bp 214 °C), suggesting that solvent additives with higher boiling points provide resultant films with preferable molecular ordering and morphologies for efficient charge transport.

Viability of stretchable poly(3-heptylthiophene) (P3HpT) for organic solar cells and field-effect transistors

Mechanical compliance is a critical attribute for organic semiconductors in flexible, stretchable, mechanically robust, and biologically integrated electronics. This paper substantially develops the observation that a small change in the length of the alkyl side chain of regioregular poly(3-alkylthiophene)s has a dramatic effect on the interplay between their mechanical and charge-transport properties. Specifically, the thermal, mechanical, and charge-transport properties of poly(3-heptylthiophene) (P3HpT, n=7), which we found to be an unusual example of a stretchable semiconducting thermoplastic, are described in comparison to those of poly(3-hexylthiophene) (P3HT, n=6) and poly(3-octylthiophene) (P3OT, n=8). Neat P3HpT was found to have mechanical properties similar to that of P3OT, and when mixed in 1:1 blends with the fullerene [6,6]-phenyl C61 butyric acid methyl ester (PCBM), exhibited electronic properties comparable to P3HT. However, the charge-carrier mobility of neat P3HpT is substantially inferior to that of P3HT; the good performance of P3HpT-based solar cells is the result of improved mobility in P3HpT:PCBM blends compared to the neat material. While P3HpT may be a favorable alternative to P3HT in ultra-flexible, stretchable, and mechanically robust organic solar cells, P3HpT would only make a good field-effect transistor in situations in which mechanical compliance was more important than high mobility.

Surface plasmon coupled metal enhanced spectral and charge transport properties of poly(3,3'''-dialkylquarterthiophene) Langmuir Schaefer films.

The coupling of organic molecule excitons with metal nano-structure surface plasmons can improve the performance of optoelectronic devices. This paper presents the effect of localized silver metal surface plasmons on spectral as well as charge transport properties of ordered molecular Langmuir Schaefer (LS) films of a fluorescent conducting multifunctional organic polymer: poly (3,3'''-dialkylquarterthiophene) [PQT-12]. The stability and thickness of the PQT-12 LS film were studied by the pressure vs. area isotherm curve. Atomic force microscopy images indicate the formation of a smooth ordered polymer thin LS film of PQT-12 over silver nanostructure island films [SNIF] (∼40 to 50 nm in size). Raman, electronic absorption and fluorescence spectral measurements of the PQT-12 LS film, near SNIF i.e. the near field, show a plasmon coupled enhancement of ∼13 fold in the intensity of Raman bands along with a two-fold enhancement in the absorption band (531 nm) and a six-fold enhancement in the fluorescence band (665 nm) coupled with a decrease in fluorescence decay time with improved photostability as compared to an identical control sample containing no SNIF i.e. the far field condition. These results indicate the formation of a plasmon coupled unified fluorophore system due to adsorption of the PQT-12 LS film over SNIF. The effect of plasmonic coupling is also studied by applying an electric field in sandwiched structures of Al/PQT-12 LS/SNIF/ITO with respect to Al/PQT-12 LS/ITO. Nearly three orders of magnitude enhancement in the current density (J-V plot) of the PQT-12 LS film is observed in the presence of SNIF, which further increases, on illuminating the film by green laser light [532 nm], while the fluorescence intensity and decay time decrease. X-ray photoelectron spectroscopic measurements of SNIF also show a red shift in 3d3/2 and 3d5/2 transitions of silver in the PQT-12 coated LS film, which indicates partial charge transfer from the PQT-12 polymer backbone to SNIF and causes an enhancement in conductivity. This again supports the formation of a field controlled radiating plasmon coupled fluorophore unified system. These findings show greater potential in developing a voltage controlled high photon flux electroluminescent material for multifarious applications.

The Role of Regioregularity, Crystallinity, and Chain Orientation on Electron Transport in a High-Mobility n-Type Copolymer

We investigated the correlation between the polymer backbone structural regularity and the charge transport properties of poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} [P(NDI2OD-T2)], a widely studied semiconducting polymer exhibiting high electron mobility and an unconventional micromorphology. To understand the influence of the chemical structure and crystal packing of conventional regioregular P(NDI2OD-T2) [RR-P(NDI2OD-T2)] on the charge transport, the corresponding regioirregular polymer RI-P(NDI2OD-T2) was synthesized. By combining optical, X-ray, and transmission electron microscopy data, we quantitatively characterized the aggregation, crystallization, and backbone orientation of all of the polymer films, which were then correlated to the electron mobilities in electron-only diodes. By carefully selecting the preparation conditions, we were able to obtain RR-P(NDI2OD-T2) films with similar crystalline structure along the three crystallographic axes but with different orientations of the polymer chains with respect to the substrate surface. RI-P(NDI2OD-T2), though exhibiting a rather similar LUMO structure and energy compared with the regioregular counterpart, displayed a very different packing structure characterized by the formation of ordered stacks along the lamellar direction without detectible π-stacking. Vertical electron mobilities were extracted from the space-charge-limited currents in unipolar devices. We demonstrate the anisotropy of the charge transport along the different crystallographic directions and how the mobility depends on π-stacking but is insensitive to the degree or coherence of lamellar stacking. The comparison between the regioregular and regioirregular polymers also shows how the use of large planar functional groups leads to improved charge transport, with mobilities that are less affected by chemical and structural disorder with respect to classic semicrystalline polymers such as poly(3-hexylthiophene).

Crystal structure and charge transport properties of poly(arylene-ethynylene) derivatives: A DFT approach

In the present study, a series of crystalline poly(arylene-ethynylene) copolymers containing phenylethynylene and 2,5-dialkoxy-phenylethynylene units together with 1,3,4-thiadiazole rings has been modeled by means of periodic calculations. Optimized three-dimensional polymeric structures show interchain distances that are consistent with the experimental values reported for a related polymer. It has also been observed that the presence of pendant alkoxy chains brings on both a further flattening and a separation of the coplanar chains. This fact is linked to a decrease of the interchain cofacial distance. The electron transport character of the polymer crystal structures was assessed through Marcus theory. Electronic coupling between neighboring polymer chains is most influenced by the presence of alkoxy chains giving rise to an expectable enhancement of the electron hopping mobility.

Properties of poly(ethylene terephthalate) track membranes with a polymer layer obtained by plasma polymerization of pyrrole vapors

The structure and the charge transport properties of poly(ethylene terephthalate) track membrane modified by pyrrole plasma were studied. It was found that polymer deposition on the surface of a track membrane via plasma polymerization of pyrrole results in the creation of composite nanomembranes that, in the case of the formation of a semipermeable layer, possess asymmetric conductivity in electrolyte solutions – a rectification effect similar to that of a p–n junction in semiconductors. It is caused by presence in the membranes of two layers with different functional groups and also by the pore geometry. Such membranes can be used to create chemical and biochemical sensors.

Preparation of composite membranes by means of plasma polymerization of tiophene

The structure and the charge transport properties of poly(ethylene terephthalate) track membranes modified in a thiophene plasma were studied. It was found that polymer deposition on the surface of a track membrane via the plasma polymerization of thiophene results in composite membranes that, in the case of the formation of a semipermeable layer, exhibit conductivity asymmetry—rectifying effect—in electrolyte solutions. It was shown that chemical doping with iodine or photo-oxidation of the polymer layer produced in plasma leads to alteration in the electrochemical properties of plasma-modified membranes.

Synthesis, Electrical, Electronic and Charge Transport Properties of Poly(aniline‐co‐p‐toluidine)

Copolymers of aniline with p‐toluidine were synthesized for different molar ratios of the respective monomers in acid medium. The electrical conductivity, charge transport and spectral characteristics upon incorporation of p‐toluidine units into the polyaniline backbone were investigated. The electrical conductivity of the copolymers showed frequency dependence which became more prominent with an increase in the number of p‐toluidine units in the polyaniline backbone. A direct relationship between the frequency dependence and electron localization was observed in the copolymers. Electronic spectra showed blue shifts in the π→π*and benzenoid→quinoid transitions revealing a decrease in the extent of conjugation in the copolymers. The protonated forms of the copolymers were soluble in DMSO giving polaron band around 400 nm. The decrease in electrical conductivity was attributed to the greater electron localizations as revealed from the broader ESR signals. Temperature dependence of electrical conductivity showed that charge transport was mainly through variable range hopping though a mixed conduction behavior was observed at higher temperature range.

Influence of composition and heat-treatment on the charge transport properties of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester blends

Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends have been demonstrated to form highly efficient polymer photovoltaic devices. In this letter, the time-of-flight technique is used to investigate the influence of composition and heat treatment on charge transport properties of P3HT and PCBM blends. The transport of electrons and holes both display a transition from dispersive to nondispersive and return to dispersive again as the percentage of PCBM increases. A balanced mobility of both electron and hole is obtained at a composition of 1:1 weight ratio, and it is nearly independent of the electrical field in the range of our test. The increase in carrier mobility is attributed to the formation of a more-ordered structure in the blend. This structural ordering is further enhanced by slowly evaporating the solvent during film formation which results in additional increase in carrier mobility. However, no such effect is observed in thick films (∼200nm), indicating the presence of such high-degree ordering due to heat treatment.

Influence of composition and heat-treatment on the charge transport properties of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester blends

Influence of composition and heat-treatment on the charge transport properties of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester blends

The synthesis, optical and charge transport properties of poly(aromatic oxadiazole)s

In this work we report the synthesis and characterization of processable poly(aromatic oxadiazole)s. The polymers are rendered processable by either dissolving the polymer in strongly acidic organic solvent or by the thermal conversion of a soluble precursor polyhydrazide. The optical and charge transporting properties of the polymers have been investigated by UV-Vis absorption, photoluminescence spectroscopy and cyclic voltammetry. All the polymers have been found to exhibit strong purple-blue fluorescence and good hole-blocking and electron-injecting properties.

Optical and charge transport properties of DI‐n‐hexyl substituted polysilylene and polygermylene

AbstractOptical and charge transport properties of poly(di‐n‐hexylsilylene), PD6S, and poly(di‐n‐hexylgermylene), PD6G, have been studied. The main‐chain σ‐conjugation in both polymers leads to intense σ‐σ* UV‐absorptions. A hypsochromic shift is observed for both polymers at the transition from a crystalline solid phase to a columnar mesophase. This transition is accompanied by disordering of the polymer backbone which results in a decrease of the radiation induced microwave conductivity by a factor of 26 for PD6S and a factor of 4 for PD6G. In the disordered mesophase a charge carrier mobility of ca. 0.6×106 m2/Vs is found for both polymers. Charge carrier mobilities of 15×106 m2/Vs and 2.4×10‐6.m2/Vs are found in the crystalline phase of PD6S and PD6G respectively, indicating a more ordered backbone for PD6S compared with PD6G.

Highly conductive crystalline poly(2-methoxy- p-phenylene vinylene)

The synthesis and the structural, thermal and charge transport properties of poly(2-methoxy- p-phenylene vinylene) (MeOPPV) are reported. An inverse emulsion polymerization procedure for the preparation of the precursor polymer is described; this method provided improved yields with higher molecular weights. Also discussed are disorder and defects in the rigid conjugated crystalline polymer revealed by infra-red spectra and X-ray diffraction. It was observed that the charge transport properties of the polymer were affected by structural disorders. Films of MeOPPV became highly conductive when oxidatively doped, and they exhibited excellent air stability. The electron-donating substitution is shown to lower the ionization potential of the parent polymer, thereby improving the stability of the doped form. Differential scanning calorimetry and variable-temperature ultra-violet/visible spectra indicated that the polymer undergoes unusual backbone motions.

Charge transport properties of poly(N-vinylimidazole) containing [Os(N)6]2+/3+ moieties

The rate of charge transport of electrodes modified with osmium containing poly(N-vinylimidazole) has been examined as a function of the nature of the contacting electrolyte solution and of temperature. Heterogeneous electron transfer from the electrode into the polymer film has also been investigated. The charge transport parameters show that the nature of the electrolyte anion and its concentration have a large impact on the polymer morphology. In sulfuric acid the films appear significantly swollen, hydrated, and porous, while in perchlorate-containing solutions they are rather compact. Activation energies for the rate-determining step of charge transport show that, depending on the electrolyte, segmental chain motion or ion movement represents the rate-limiting process.

The effect of electrolyte‐controlled growth morphology on the charge transport properties of poly(3‐methylthiophene)

AbstractPoly(3‐methylthiophene) films were potentiostatically and galvanostatically synthesized on platinum electrodes in acetonitrile using lithium perchlorate, lithium tetrafluoroborate, tetra‐n‐butylammonium perchlorate, and tetra‐n‐butylammonium tetrafluoroborate as supporting electrolytes. Cyclic voltammetric analyses of the polymer films indicate the synthesis is polymerization process dependent. Constant potential syntheses, which resulted in a higher current density and were carried out at higher potentials, yielded polymer films with a higher charge capacity. Chronocoulometric results show that the charge transport rates of the films were electrolyte dependent and that tetra‐n‐butylammonium tetrafluoroborate yielded poly(3‐methyl‐thiophene) with the highest charge transport rate. The charge transport rate was found to be electric field dependent for all cases, suggesting that the films resemble a porous electrode. Scanning electron microscope analyses of the films, prepared under various conditions, indicate that the synthesis method used, and the nature of the electrolyte, strongly influence morphology and charge transport.