Charge transport in polyaniline doped with 3-nitro-1,2,4-triazol-5(4H)-one

Polyaniline (PANI) base was protonated in aqueous solutions of an organic acid, 3-nitro-1,2,4-triazol-5(4H)-one (NTO). The temperature dependence of DC conductivity of PANI-NTO seems to correspond to the theory of variable range hopping (VRH) in three dimensions. The frequency dependence of AC conductivity also reflects the hopping nature of mobile charges. The activation energy for the polymers with protonation degree above 0.12 remains constant with increasing dopant concentration and DC conductivity. The value of this constant may correspond to the energy needed for the ionization of dopant counterion. The fit of the electric relaxation function to the stretched exponential function ϕ(t) = exp[−(t/τ)^β] gives the stretch parameter β about 0.35, which shows that the distribution of relaxation times is broad and indicates a high inhomogeneity in the distribution of a dopant.     

Effect on Charge Transfer and Charge Recombination by Insertion of a Naphthalene‐Based Bridge in Molecular Dyads Based on Borondipyrromethene (Bodipy)

The photophysical properties of two related dyads based on a N,N‐dimethylaniline donor coupled to a fully‐alkylated boron dipyrromethene (Bodipy) acceptor are described. In one dyad, BD1 , the donor unit is attached directly to the Bodipy group, whereas in the second dyad, BD2 , a naphthalene spacer separates the two units. Cyclic voltammograms recorded for the two dyads in deoxygenated MeCN containing a background electrolyte are consistent with the reversible one‐electron oxidation of the N,N‐dimethylaniline group and the reversible one‐electron reduction of the Bodipy nucleus. There is a reasonable driving force (ΔG_CT) for photoinduced charge transfer from the N,N‐dimethylaniline to the Bodipy segment in MeCN. The charge‐transfer state is formed for BD1 extremely fast (1.5 ps), but decays over 140 ps to partially restore the ground state. On the other hand, the charge‐transfer state for BD2 is formed more slowly, but it decays extremely rapidly. Charge recombination for both dyads leads to a partial triplet formation on the Bodipy group. The naphthalene spacer group is extremely efficient at promoting back electron transfer.     

Cruciform oligo(phenylenevinylene) with a bipyridine bridge: synthesis, its rhenium(I) complex and photovoltaic properties

A cruciform-shaped oligo(phenylenevinylene) (OPV) with a phosphorescent rhenium(I) chromophore incorporated at the centre and grafted triphenylamines around the periphery was designed as a new organic photovoltaic material, in which the chelation of rhenium(I) to the cruciform successfully constructs a three-dimensional intramolecular charge transfer system and extends the exciton lifetime; as a result, the rhenium-OPV complex shows a power conversion efficiency almost two times that of the metal ion-free parent compound.     

Charge transport properties of MDMO PPV thin films cast in different solvents

Charge transport properties in thin films of Poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene) (MDMO PPV) cast using either chloroform (CF), toluene (TOL), or chlorobenzene (CB) as solvent were investigated. Hole mobility (μ) in these thin films measured using time‐of‐flight transient photoconductivity showed an increasing trend with respect to the solvent used in the same order, that is, μ_CF (2.4 × 10^?7 cm²/Vs) < μ_TOL (6.9 × 10^?7 cm²/Vs) < μ_CB (2.3 × 10^?6 cm²/Vs). Observed variations in mobilities were attributed to different morphologies of MDMO PPV chains in thin films cast using the aforesaid solvents. Nature of the interchain interactions and aggregate formation were obtained using photoluminescence (PL), Raman spectroscopy, and AFM studies. Ratio of PL peak intensities of 0–0 and 0–1 transitions, which is a direct measure of interchain interaction, was the highest in CB and lowest in CF. Variation in the relative intensities of out‐of‐plane wagging of vinylene group (～963 cm^?1 mode) in Raman spectra suggested different extent of coiling of polymer chains in these thin films. From these observations, it was elicited that aggregate size and interchain interactions are highest in CB and least in CF. AFM‐based topographic images of thin films further supported these variations in the size of aggregates. Variation in the aggregate sizes and interchain interactions explained the corresponding variation in the mobility. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1431–1439     

Photophysical characteristics of soluble oligo(p‐phenylenevinylene)–fullerene dyad

The fact that C₆₀ is a good acceptor has stimulated interest in covalently linked complexes, including polymers and oligomers. Photoinduced charge transfer in these systems has great potential for use in photovoltaic devices. In this study, an alternating conjugated oligomer of alkylated carbazole and dialkoxyl‐substituted phenylene, with pendant C₆₀ moieties, (PPV‐AFCAR) was prepared and characterized. The excited‐state properties of PPV–AFCAR were investigated with steady‐state spectroscopy and lifetime measurements. After photoexcitation, photoinduced energy transfer from the oligomer chain to the pendant moiety occurred in great proportion, but a charge‐separation process did not. Whether the energy‐transfer process was measurable or not depended on the system temperature. At 77 K, a quantum yield of more than 50% for energy transfer was found by the fitting of a linear combination of the excitation spectra of the precursor oligomer, the alternating conjugated oligomer of alkylated carbazole and dialkoxyl‐substituted phenylene PPV–ACAR, and the absorption spectra of C₆₀. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3981–3988, 2001     

Charge transport properties for carbazolyl groups pendant poly(glutamate)

Carbazolyl groups pendant poly(glutamate) (PCLG) was prepared to analyze its charge‐transport properties by employing mobility measurements and thermally‐stimulated current (TSC) measurements. The mobility induced TSC (MITSC) model proposed by I.Chen was employed to evaluate the experimental TSC spectra with mobility results. Simulated MITSC spectra showed good agreement in its peak temperature with experimental TSC spectra for PCLG. This suggests that the carrier transport followed the trap‐limited mechanism estimated by the mobility results. Further, the peaks in experimental TSC spectra appeared over the same temperature range as that in thermally‐stimulated polarization current (TSPC) spectra. Since the TSPC spectra were found to be correlated with the dielectric tan δ spectra for PCLG, the peaks in TSPC spectra are attributed to the side‐chain relaxation for PCLG. Therefore, the similarity between TSPC and TSC spectra indicates that the charge‐transport mechanism for PCLG was considerably affected by side‐chain relaxation for PCLG, which would vary the energy state of trap sites and effectively reduces the energy for the release of the carriers trapped on the illuminated surface. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 61–69, 1999     

Poly(p‐phenylenevinylene) Derivatives with Defined Conjugation Segments and Post‐Polymerization Modification with Sterically Enshrouded Chromophores

Two poly(p‐phenylenevinylene) derivative alternating copolymers ( P1‐I and P2‐I ) have been prepared featuring iodo substituents and m‐phenylene units to periodically disrupt conjugation. P1‐I was derivatized with various chromophores to yield P1a‐f . In P1a‐f , the chromophores were positioned within a sterically protected pocket shielding them from interchain interactions so that intrachain interactions between polymer segments could be observed. Solution and film properties of polymers have been examined. Post‐polymerization chromophore modification leads to new photophysical properties such as intramolecular charge transfer and fluorescent resonance energy transfer processes in some cases.

     

Charge transport properties in carbon black/polymer composites

The charge transport properties of polymer matrix–carbon black composites are investigated in this study. Direct current conductivity is examined with varying parameters: the temperature and the conductive filler content. Conductivity data are analyzed by means of percolation theory, and both percolation threshold and critical exponent are determined at each of the examined temperatures. The temperature dependence of conductivity and the agreement of experimental results with the variable range hopping model reveal hopping conduction as the predominant transport mechanism, below and in the vicinity of the critical concentration of carbon black particles. At higher concentrations, the contribution of hopping transport to the overall conductivity is reduced and a balance between hopping and conduction via geometrical contact occurs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2535–2545, 2007     

Synthesis and photovoltaic properties of poly(p‐phenylenevinylene) derivatives containing oxadiazole

A novel poly(p‐phenylenevinylene) PPV‐based copolymer (3C‐OXD‐PPV) with electron‐deficient oxadiazole segments as the side chain has been successfully synthesized through the Gilch polymerization. The obtained copolymer is soluble in common organic solvents such as chloroform, tetrahydronfuran, and 1,1,2,2‐tetrachloroethane. The copolymer was characterized by ¹H NMR, elemental analysis and GPC. TGA measurement of the copolymer shows it has good thermal stability with decomposition temperature higher than 350 °C. The absorption, electrochemical properties of the 3C‐OXD‐PPV were investigated and also compared with the properties of MEH‐PPV. The HOMO and LUMO levels of 3C‐OXD‐PPV were estimated from the electrochemical cyclic voltammograms. Bulk‐heterojunction PVCs were fabricated by using 3C‐OXD‐PPV blended PCBM as an active layer. The PCE of the PVC is 1.60% under 100 mW cm^?2 AM 1.5 illumination, which indicates that 3C‐OXD‐PPV is a potential candidate for the application of polymer PVC. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1003–1012, 2009     

Charge carrier transport in poly[methyl(phenyl)silylene]: the effect of additives

Poly[methyl(phenyl)silylene], PMPSi, was doped with compounds of the electron acceptor type. The charge carrier mobility increases with increasing electron affinity of the acceptors having zero dipole moments. At the same time the energy distribution of hopping states narrows. On the other hand, the hole drift mobility is influenced by the dipole moment of the dopand. The electrostatic charge carrier‐dipole interaction causes a broadening of the energy distribution of transport states which results in a decrease in the charge carrier mobility. The charge carrier transport can be explained by the disordered polaronic theory, according to which the activation energy of charge carrier mobility has contributions based on the dynamic disorder, i.e. the polaronic barrier, and on the static disorder, i.e. the variation of the energy of transport states as a result of the environment. Copyright © 2001 John Wiley & Sons, Ltd.     

Charge transport in poly(methylphenylsilane): The case for superimposed disorder and polaron effects

Careful analysis of the temperature dependence of the hole mobility in poly (methylphenylsilane) indicates that the functional dependence is between an Arrhenius law and a ln μ ∝ T^?2 law as predicted by a model of disorder-controlled hopping. This is attributed to the superposition of disorder and polaron effects. A method is presented for separating the two contributions. The evolution of time-of-flight photocurrent transients with decreasing temperature is consistent with the disorder parameter derived from the temperature dependence of the mobility. © 1994 John Wiley & Sons, Inc.     

Charge transport and contact resistance in coplanar devices based on colloidal polyaniline dispersion

The charge transport properties of thin films prepared from colloidal dispersion of polyaniline stabilized by poly(N‐vinylpyrrolidone) (PANI/PVP) have been investigated. The electrical characterization of coplanar device comprising of gold electrodes and PANI/PVP film deposited by spin coating served to gain insights into the contact and bulk resistance. The films prepared from PANI/PVP colloidal dispersion show high stability over a large temperature range. Temperature dependent measurements in the range from 90 to 350 K reveal that the charge transport can be described by a three‐dimensional variable‐range hopping mechanism as the dominant mode in the films. The stability of the films cast from dispersion within a large temperature range opens the possibility of the application as a polymer semiconductor layer in sensors and charge‐transport interlayer in organic solar cells. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1710–1716     

Charge transport and structure in semimetallic polymers

Owing to changes in their chemistry and structure, polymers can be fabricated to demonstrate vastly different electrical conductivities over many orders of magnitude. At the high end of conductivity is the class of conducting polymers, which are ideal candidates for many applications in low‐cost electronics. Here, we report the influence of the nature of the doping anion at high doping levels within the semi‐metallic conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT) on its electronic transport properties. Hall effect measurements on a variety of PEDOT samples show that the choice of doping anion can lead to an order of magnitude enhancement in the charge carrier mobility > 3 cm²/Vs at conductivities approaching 3000 S/cm under ambient conditions. Grazing Incidence Wide Angle X‐ray Scattering, Density Functional Theory calculations, and Molecular Dynamics simulations indicate that the chosen doping anion modifies the way PEDOT chains stack together. This link between structure and specific anion doping at high doping levels has ramifications for the fabrication of conducting polymer‐based devices. © 2017 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 97–104     

Acetone transport in poly(ethylene terephthalate) and related phenomena

The acetone transport in poly(ethylene terephthalate) (PET) and related phenomena was investigated. Based on Harmon's model for Case I, Case II, and the anomalous transport, we analyzed the data of mass uptake. The diffusivity for Case I and the velocity for Case II satisfied the Arrhenius plot. It was found that the solvent moves from outer surfaces to the center according to Case I kinetics, and there is movement in the opposite direction according to Case II kinetics during the mass uptake. This result indicated that pure Case II behavior did not appear in the PET–acetone system. The saturated amount of acetone in PET satisfied the van't Hoff plot. X-ray diffraction pattern and DSC curve showed solvent-induced crystallites and thermal crystallites. The results of density measurement explained the difference of the sorption kinetics between the acetone-treated PET crystallites and thermally treated PET. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 163–169, 1998     

Novel low‐bandgap oligothiophene‐based donor‐acceptor alternating conjugated copolymers: Synthesis,properties, and photovoltaic applications

A series of novel soluble donor‐acceptor low‐bandgap‐conjugated polymers consisting of different oligothiophene (OTh) coupled to electron‐accepting moiety 2‐pyran‐4‐ylidenemalononitrile (PM)‐based unit were synthesized by Stille or Suzuki coupling polymerization. The combination of electron‐accepting PM building block with varied OTh_n (the number of thiophene unit increases from 3 to 5) results in enhanced π–π stacking in solid state and intramolecular charge transfer (ICT) transition, which lead to an extension of the absorption spectra of the copolymers. Cyclic voltammetry measurements and molecular orbital distribution calculations indicate that the highest occupied molecular orbitals (HOMO) energy levels could be fine‐tuned by changing the number of thiophene units of the copolymers, and the resulting copolymers possessed relatively low HOMO energy levels promising good air stability and high‐open circuit voltage (V_oc) for photovoltaic application. Bulk heterojunction photovoltaic devices were fabricated by using the copolymers as donors and (6,6)‐phenyl C₆₁‐butyric acid methyl ester as acceptor. It was found that the highest V_oc reached 0.94 V, and the short circuit currents (J_sc) were improved from 1.78 to 2.54 mA/cm², though the power conversion efficiencies of the devices were measured between 0.61 and 0.99% under simulated AM 1.5 solar irradiation of 100 mW/cm², which indicated that this series copolymers can be promising candidates for the photovoltaic applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2765–2776, 2010     

Synthesis and optical and transport properties of a phenyl‐substituted polythiophene

The synthesis and characterization of a novel polythiophene substituted with a 2′‐pentyloxy‐5′‐(1″′‐oxooctyl) phenyl group (PPOPT) is reported. The bulk transport properties of thin films of PPOPT are investigated by admittance spectroscopy. The dramatic effect of the phenyl side chain on the mobility of positive carriers in films of PPOPT is described. The photophysics of PPOPT in both solution and thin film is also investigated and correlated to substituent‐driven intrachain and interchain arrangements. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Interface configuration effects on excitation,exciton dissociation,and charge recombination in organic photovoltaic heterojunction

The morphology of donor-acceptor heterojunction interface significantly affects the electron/hole processes in organic solar cells, including charge transfer (CT), exciton dissociation (ED), and charge recombination (CR). Here, to investigate interface molecular configuration effects, the donor-acceptor complexes with face-on, edge-on, and end-on configurations were constructed as model systems for the p-SIDT(FBTTh₂)₂/C₆₀ heterojunction. The geometries, electronic structures, and excitation properties of monomers and the complexes with three configurations were studied based on density functional theory (DFT) and time-dependent DFT calculations with optimally tuned range separation parameters and solid polarization effects. In terms of Marcus theory, the rate constants of ED and CR processes were analyzed. The results show that most of the excited states for p-SIDT(FBTTh₂)₂ exhibit an intramolecular CT character, and the similarity of the excitation characters (CT and local excitation) and energies among three complexes with different configurations indicate that the electronic structure and excitation properties are insensitive to the interfacial molecular configurations. However, the rates of ED and CR processes heavily depend on it. These results underline the importance of controlling molecular configuration and then the morphology at the heterojunction interface in organic solar cells.     

Effect of molecular weight in diketopyrrolopyrrole‐based polymers in transistor and photovoltaic applications

Uncovering the precise effect of the conjugated polymer chain length on the semiconducting properties in thin‐film devices is confounded by the step‐growth polymerization techniques typically used. Here, we use preparatory size exclusion chromatography to isolate fractions of two diketopyrrolopyrrole‐thiophene based co‐polymers with low molar‐mass dispersity, ?_M, and number average molecular weights up to 180 kDa. We find that the charge carrier mobility can vary over three orders of magnitude in the range from 9 to 70 kDa, while a factor of 3–4 increase in photovoltaic performance was noted over the same range. The effect of ?_M was found to be most drastic when the largest chains were mixed with the shortest. The study of the thin‐film morphology and crystallinity by GIWAXS give further insights into the origin of these effects. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2245–2253     

Charge carrier mobility,photovoltaic, and electroluminescent properties of anthracene‐based conjugated polymers bearing randomly distributed side chains

This article reports on the synthesis, characterization, and properties of various anthracene‐containing poly (p‐phenylene‐ethynylene)‐alt‐poly(p‐phenylene‐vinylene) (PPE‐PPV) polymers (AnE‐PVs) bearing statistical distributions of various side chains. Primarily, the ratio of linear octyloxy and branched 2‐ethylhexyloxy side chains at the poly(p‐phenylene vinylene) (PPV) parts was varied, leading to the polymers stat, stat1, and stat2. Furthermore, polymers also containing asymmetric substituted PPV and poly(p‐phenylene ethynylene) units (bearing methoxy and 2‐ethylhexyloxy side chains) were prepared yielding stat3, stat4, and stat5. These materials exhibit a broad variation in their photovoltaic properties. It is once more shown that side chains and their distribution can crucially affect the photovoltaic device performance. The introduction of units with asymmetric substitution into these systems seems to be harmful for their utilization in photovoltaic applications. Organic field‐effect transistors were fabricated to investigate hole mobilities in these new materials. Large variance was observed, falling in the range of almost two orders of magnitude, indicating rather different π–π stacking behavior of the polymer backbones owing to side‐chain modifications. Moreover, a selection of the new polymeric systems was investigated regarding their potential for light‐emitting diode (LED) applications. Polymer LEDs using the polymers AnE‐PVstat, ‐stat3, ‐stat4, and ‐stat5, as the active layer showed turn‐on voltage of ～2 V and exhibited red light emission. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012