The origin of DC electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) films

We present here the evidence for the origin of dc electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) (P3HT) films. P3HT has been synthesized and purified to obtain pristine P3HT polymer films. P3HT films are chemically doped to make conducting P3HT films with different conductivity level. Temperature (77–350 K) dependent dc conductivity (σ_dc) and dielectric constant (ε′(ω)) measurements on pristine and doped P3HT films have been conducted to evaluate dc and ac electrical conduction parameters. The relaxation frequency (f_R) and static dielectric constant (ε₀) have been estimated from dielectric constant measurements. A correlation between dc electrical conduction and dielectric relaxation data indicates that both dc and ac electrical conductions originate from the same hopping process in this system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1047–1053, 2010     

Electrical transport properties of semiconducting lithium molybdate glass nanocomposites

We have reported the formation of lithium molybdate glass nanocomposites embedded with lithium molybdate nanophases from the x-ray diffraction and transmission electron microscopic studies. We have investigated the dc electrical conductivity in a wide temperature range for these glass nanocomposites, which exhibit semiconducting behavior. We have analyzed the dc electrical data in the light of polaronic conduction models of Mott and Schnakenberg. We have also studied ac electrical conductivity of these glass nanocomposites in wide temperature and frequency ranges. The experimental ac results have been analyzed with reference to various theoretical models based on quantum-mechanical tunneling and hopping over the barrier. We have observed that the temperature dependence of the dc conductivity is consistent with the polaronic hopping models, while the temperature and frequency dependence of the ac conductivity is consistent with the polaronic tunneling models.     

Role of surface modification of colloidal CdSe quantum dots on the properties of hybrid organic–inorganic nanocomposites

In this work, tri-octyl phosphine/tri-octyl phosphine oxide (TOPO)-capped cadmium selenide (CdSe) quantum dots (QDs) of varied sizes (5–9 nm), prepared by varying the input Cd:Se precursor ratio using chemical route, were dispersed in conducting polymer matrices viz. poly[2-methoxy, 5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and poly(3-hexylthiophene) (P3HT). By using a binary solvent mixture (pyridine–chloroform), homogeneous dispersion of CdSe nanocrystals in polymers (MEH-PPV, P3HT) could be realized. The properties of the resulting dispersions could be tailored by the composition and concentration of QDs in polymer. The emission and structural properties of polymer–CdSe nanocomposites are found to be dependent on the crystallite size and morphology of CdSe nanocrystallites. An effective quenching of photoluminescence emission in the polymer nanocomposite was observed for smaller CdSe quantum dots (size ∼6 nm) as compared to larger CdSe quantum dots (size ∼9 nm), thus ensuring efficient charge transfer process across the polymer–CdSe interface in the former case. The incomplete quenching, particularly for MEH-PPV:CdSe nanocomposites, could be as a result of insufficient coverage of polymers on the surface of CdSe nanocrystallites, mainly due to phase segregation for TOPO-stripped CdSe nanocrystallites. The superior morphology and optical properties of polymer nanocomposite (P3HT:CdSe QDs) could play a pivotal role for the realization of effective charge separation and transport in hybrid solar cells.     

Ultrafast photoinduced charge separation dynamics in polythiophene/SnO2 nanocomposites

We present a study of photoinduced interfacial electron transfer (ET) dynamics of SnO2 nanocrystalline thin films sensitized by polythiophene derivatives (regioregular poly(3-hexylthiophene) (P3HT) and regiorandom poly(3-undecyl-2,2'-bithiophene) (P3UBT)). ET dynamics were measured by following the dynamics of injected electrons in SnO2 and polarons in the conjugated polymer using ultrafast mid-IR transient absorption spectroscopy. The rate of electron transfer from P3HT and P3UBT to SnO2 films was determined to occur on sub-picosecond time scale (120 +/- 20 fs). In P3HT/SnO2 composite, interchain charge transfer was found to compete with and reduce the quantum efficiency of interfacial electron transfer at high polymer loading. This interchain charge separation processes can be reduced in non-regioregular polymer or at low polymer loading levels.     

Frequency‐dependent conductivity of interpenetrating polymer network composites of polypyrrole–poly(vinyl acetate)

The frequency‐dependent conductivity of interpenetrating polymer network composites of polypyrrole (PPy) and poly(vinyl acetate) (PVAc) synthesized by FeCl₃‐impregnated PVAc films being dipped into solutions of pyrrole in water was investigated over a frequency range of 100 Hz to 2 MHz and a temperature range of 110–300 K. For specimens with a PPy content less than the percolation threshold, the quantum mechanical tunneling of electrons was the conduction mechanism. For specimens with a higher PPy content, correlated barrier hopping of electrons appeared to be operative. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1935–1941, 2001     

Structural hierarchy in melt-processed poly(3-hexyl thiophene)-montmorillonite clay nanocomposites: novel physical, mechanical, optical, and conductivity properties

Poly(3-hexyl thiophene) (P3HT) organically modified montmorillonite (om-MMT) polymer nanocomposites (PNCs) are prepared in the melt-cooled state. Hierarchical structures up to third order, namely, side chain mesomorph formation followed by the interchain lamellar structure of P3HT and finally its intercalation within the clay tactoids are observed. The structures are supported by transmission electron microscopy (TEM) and wide-angle X-ray scattering (WAXS) experiments. The TGA curves show two-stage degradation corresponding to those of the side chain and main chain of P3HT, and both temperatures decrease with an increase in clay concentration in the PNCs. The melting points of PNCs have increased by 2-3 degrees C higher than that of P3HT. The glass-transition temperature (Tg) and beta-transition temperature (Tbeta), measured by DMA, increase with an increase in clay concentration. The storage modulus (G) of PNCs has also increased more dramatically than that of P3HT. The UV-vis spectra of the PNCs show a blue shift in the pi-pi* absorption peak of the conjugated chain, but the photoluminescence spectra showed a red shift with an increase in the clay concentration. The quantum yield of the photoluminescence process also increases in the melt-cooled PNCs, and this is in sharp contrast to that of solvent cast PNCs where photoluminescence quenching was observed. Fibrillar network structure of the solvent cast PNCs promotes energy transfer of the charge carriers, but its absence in the melt-cooled films inhibits such energy transfer, increasing the quantum yield. The room-temperature dc conductivity of the PNCs decreased by an order compared to that of P3HT in both the doped and undoped states. The I-V characteristic curve shows semiconducting behavior, and it slowly transforms into insulator with increasing clay concentration.     

Synthesis,characterization, dielectric and rectification properties of PANI/Nd2O3:Al2O3 nanocomposites

Polyaniline–Nd₂O₃:Al₂O₃ nanocomposites were prepared by in situ oxidative polymerization method using different weight percentages of oxide powders. The prepared nanocomposites were characterized by Fourier transform infrared spectroscopy and X‐ray diffraction for molecular and crystal structures. Scanning electron microscopy and transmission electron microscopy images show the tubular structure of polyaniline nanocomposite with embedded metal oxides. The electrical conductivity of the nanocomposites increases with increase in temperature as well as with concentration of Nd₂O₃:Al₂O₃ particles in polyaniline. This is because of the hopping of charge polarons and extended chain length of the nanocomposites as evidenced by the negative thermal coefficient (NTC) characteristic. A high NTC value of 2.67 was found in nanocomposites with 15 wt% of oxide particles. These nanocomposites show low dielectric constant and dielectric loss; the electrical conductivity is higher than 0.3 S/cm as confirmed by Cole–Cole plot that indicates a decrease in both grain resistance and bulk resistance of the nanocomposites. The current–voltage and capacitance–voltage measurements were also carried out. The carrier mobility μ values of pure polyaniline and nanocomposites were found to be 4.27 × 10^?3 and 1.45 × 10^–2 H.M^?1, respectively. A significant enhancement in carrier mobility was observed in comparison with the literature. Copyright © 2016 John Wiley & Sons, Ltd.     

Imparting Multifunctionality by Utilizing Biporosity in a Zirconium-Based Metal–Organic Framework

In this work, we have synthesized nanocomposites made up of a metal–organic framework (MOF) and conducting polymers by polymerization of specialty monomers such as pyrrole (Py) and 3,4-ethylenedioxythiophene (EDOT) in the voids of a stable and biporous Zr-based MOF ( UiO-66 ). FTIR and Raman data confirmed the presence of polypyrrole ( PPy ) and poly3,4-ethylenedioxythiophene ( PEDOT ) in UiO-66-PPy and UiO-66-PEDOT nanocomposites, respectively, and PXRD data revealed successful retention of the structure of the MOF. HRTEM images showed successful incorporation of polymer fibers inside the voids of the framework. Owing to the intrinsic biporosity of UiO-66 , polymer chains were observed to selectively occupy only one of the voids. This resulted in a remarkable enhancement (million-fold) of the electrical conductivity while the nanocomposites retain 60–70 % of the porosity of the original MOF. These semiconducting yet significantly porous MOF nanocomposite systems exhibited ultralow thermal conductivity. Enhanced electrical conductivity with lowered thermal conductivity could qualify such MOF nanocomposites for thermoelectric applications.     

DC electrical conduction and morphological behavior of counter anion‐governed genesis of electrochemically synthesized polypyrrole films

Highly conducting polypyrrole (PPY) films, doped with various anions [pTS^?, ClO₄^?, and NO₃^? and mixed electrolyte system (pTS^? + ClO₄^?)], have been electrochemically synthesized in aqueous solution at ～275 K in an inert atmosphere. PPY exhibits metallic order dc conductivity at room temperature and shows variation of conductivity with respect to time of polymerization. Effect of dopant anion on growth mechanism of PPY is evident from its surface morphology. X‐ray photoelectron spectroscopy (XPS), used to examine the surface composition and doping level of various PPY films, confirms the anionic doping into the polymer backbone. Both XPS and ultraviolet–visible spectroscopy give evidence of formation of polarons and bipolarons. The temperature (4.2–320 K)‐dependent dc conductivity data of these PPY films have been explained by Mott's 3D variable‐range hopping conduction model. Mott's parameters have been estimated, and structural disorder with doping is correlated for all the samples. Mott's criterion for distant hopping sites prevails in case of moderately doped samples (PPY3, PPY4, and PPY5), whereas the hopping to nearest neighbor sites is found more suitable in case of highly doped samples (PPY1 and PPY2). The origin of these changes is due to the modification in the molecular structure of PPY, which is governed by different growth mechanisms for organic (pTS^?) and inorganic (ClO₄^? and NO₃^?) counter anions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Conductivity and modulus formulation in lithium modified bismuth zinc borate glasses

The conductivity and modulus formulation in lithium modified bismuth zinc borate glasses with compositions xLi₂O–(50-x) Bi₂O₃–10ZnO–40B₂O₃ has been studied in the frequency range 0.1 Hz–1.5 × 10⁵ Hz in the temperature range 573 K–693 K. The temperature and frequency dependent conductivity is found to obey Jonscher's universal power law for all the studied compositions, the dc conductivity (σ_dc), crossover frequency (ω_H), and frequency exponent (s) have been estimated from the fitting of the experimental data of ac conductivity with Jonscher's universal power law. Enthalpy to dissociate the cation from its original site next to a charge compensating centre (H_f) and enthalpy of migration (H_m) have been estimated. It has been observed that number of charge carriers and ac conductivity in the lithium modified bismuth zinc borate glasses increases with increase in Li₂O content. Further, the conduction mechanism in the glass sample with x = 0 may be due to overlapping large polaron tunneling, whereas, conduction mechanism in other studied glass samples more or less follows diffusion controlled relaxation model. The ac conductivity is scaled using σ_dc and ω_H as the scaling parameter and is found that these are suitable scaling parameter for conductivity scaling. Non-Debye type relaxation is found prevalent in the studied glass system. Scaling of ac conductivity as well as electric modulus confirms the presence of different type of conduction mechanism in the glass samples with x = 0 and 5 from other studied samples. The activation energy of relaxation (E_R) and dc conductivity (E_dc) are almost equal, suggesting that polarons/ions have to overcome same barrier while relaxing and conducting.     

Chemically modified polyaniline nanocomposites by poly(2-acrylamido-2-methyl-1-propanesulfonicacid)/graphene nanoplatelet

New conducting polyaniline (PANI) nanocomposites that were chemically modified by poly(2-acrylamido-2-methyl-1-propanesulfonicacid) (PMP) and graphene nanoplatelets (GNPs) were prepared via in situ deposition. PMP was first synthesized using GNPs, and aniline hydrochloride monomer was then polymerized in the presence of PMP-GNPs. The nanopolymer composites were characterized, and its structural morphology was analyzed via transmission electron microscopy and scanning electron microscopy. Fourier transformation infrared spectroscopy results indicate a strong interaction between PANI, PMP, and GNPs. To understand the conduction behavior of the composites, temperature-dependent DC electrical conductivity was measured between 295 K and 503 K, and the mechanism of transport properties of the new composites was analyzed by Mott’s variable range of hopping model. The PANI/PMP-GNP showed higher conductivity than pure PANI polymer. The high electrical conductivity of the nanocomposites may be useful in fabricating multifunctional materials in bulk for future technological applications.     

Imparting Multifunctionality by Utilizing Biporosity in a Zirconium‐Based Metal–Organic Framework

In this work, we have synthesized nanocomposites made up of a metal–organic framework (MOF) and conducting polymers by polymerization of specialty monomers such as pyrrole (Py) and 3,4‐ethylenedioxythiophene (EDOT) in the voids of a stable and biporous Zr‐based MOF ( UiO‐66 ). FTIR and Raman data confirmed the presence of polypyrrole ( PPy ) and poly3,4‐ethylenedioxythiophene ( PEDOT ) in UiO‐66‐PPy and UiO‐66‐PEDOT nanocomposites, respectively, and PXRD data revealed successful retention of the structure of the MOF. HRTEM images showed successful incorporation of polymer fibers inside the voids of the framework. Owing to the intrinsic biporosity of UiO‐66 , polymer chains were observed to selectively occupy only one of the voids. This resulted in a remarkable enhancement (million‐fold) of the electrical conductivity while the nanocomposites retain 60–70 % of the porosity of the original MOF. These semiconducting yet significantly porous MOF nanocomposite systems exhibited ultralow thermal conductivity. Enhanced electrical conductivity with lowered thermal conductivity could qualify such MOF nanocomposites for thermoelectric applications.     

Ligand-exchange dependent properties of hybrid nanocomposites based on luminescent colloidal CdSe nanocrystals in P3HT matrix

In this work, a suitable ligand-exchange process has been proposed which elucidates the possibility to modulate charge/energy transfer rate between polymer and semiconductor quantum dots. The photoluminescence studies of CdSe emission as well as transient absorption measurements confirm mainly electron transfer for P3HT:CdSe (TOPO) and electron/energy transfer for P3HT:CdSe (OA) nanocomposites, respectively. The dominance of charge transfer for P3HT:CdSe (TOPO) as compared to P3HT:CdSe (OA) nanocomposites can be attributed to complete and partial removal of the surface ligands (TOPO, OA) upon ligand exchange with pyridine as elucidated from FTIR results. The various characterization techniques viz. Fourier transform infrared (FTIR), Raman, photoluminescence (PL), optical and transient absorption (UV-Vis and TA) spectroscopies used in this work provide an insight into the charge separation, charge accumulation and/or trapping of charge carriers for the better understanding of hybrid organic-inorganic photovoltaics. Composites of CdSe (OA) quantum dots in particular with P3HT polymer owing to its higher crystallinity and ordered morphology provide a new and promising direction toward developing effective light energy harvesting strategies in organic photovoltaics.     

导电高分子纳米复合材料

导电高分子纳米复合材料是纳米材料研究中一个重要部分。着重综述了导电高分子无机纳米复合材料在合成技术、材料性质和各领域中应用的最新研究进展。     

共轭聚合物薄膜中光生载流子的产生及输运机制

对共轭聚合物光生载流子的产生机制进行了初步探讨,分析了由最初产生的电子 空穴对经过晶格驰豫之后形成极化子 激子的热离化过程,认为同一链上的激子会迅速复合,只有链间激子对光电流作出贡献.研究了共轭聚合物中载流子的输运机制,导出了共聚物的电导率公式,其计算值与实验结果符合,我们认为是极化子的链间跃迁实现了整个共聚物的电导和光致发光,较好地解释了实验事实.     

Thermal and electrical behaviors of acid functionalized MWCNT/ABC-type triblock copolymer grafted-MWCNT nanocomposites

In this work, ABC-type triblock copolymer grafted onto the surface of the MWCNT/acid functionalized MWCNT (MWCNT-COOH) composites were prepared and the properties of nanocomposites were characterized extensively using differential scanning calorimetry (DSC), scanning electronic microscopy (SEM), thermogravimetric analysis (TGA), ac electrical conductivity and dielectrical measurements.

DSC study showed that the glass transition temperatures of the nanocomposites are a some higher than that of the matrix polymer. The increase in oxidized MWCNT in the nanocomposite improved the thermal stability of the composite, according to initial decomposition temperatures. The ac electrical conductivity has increased moderately with increasing frequency, but has increased slowly with increase in the oxidized MWCNT content in the nanocomposites. The electrical conductivity increases slowly with increasing temperature to about the glass transition temperature, then it increases faster. The dielectric constants for the matrix polymer and all the composites decreases slightly with increasing frequency from 0.1 kHz to 2.0 kHz. The dielectric constant increases slightly with increasing temperature up to about the glass transition temperature region and then the increase in temperature is accelerated the increase in the dielectric constant.     

Enhanced zinc ion transport in gel polymer electrolyte: effect of nano-sized ZnO dispersion

The effect of the dispersion of zinc oxide (ZnO) nanoparticles in the zinc ion conducting gel polymer electrolyte is studied. Changes in the morphology/structure of the gel polymer electrolyte with the introduction of ZnO particles are distinctly observed using X-ray diffraction and scanning electron microscopy. The nanocomposites offer ionic conductivity values of >10^?3 S cm^?1 with good thermal and electrochemical stabilities. The variation of ionic conductivity with temperature follows the Vogel–Tamman–Fulcher behavior. AC impedance spectroscopy, cyclic voltammetry, and transport number measurements have confirmed Zn²⁺ ion conduction in the gel nanocomposites. An electrochemical stability window from ?2.25 to 2.25 V was obtained from voltammetric studies of nanocomposite films. The cationic (i.e., Zn²⁺ ion) transport number (t ₊) has been found to be significantly enhanced up to a maximum of 0.55 for the dispersion of 10 wt.% ZnO nanoparticles, indicating substantial enhancement in Zn²⁺ ion conductivity. The gel polymer electrolyte nanocomposite films with enhanced Zn²⁺ ion conductivity are useful as separators and electrolytes in Zn rechargeable batteries and other electrochemical applications.     

Synthesis and photocatalytic activity of poly(3-hexylthiophene)/TiO2 composites

An heterogeneous conducting polymer composite, poly(3-hexylthiophene)/TiO₂ (P3HT/TiO₂), was synthesized. The photocatalytic activity of P3HT alone and the composite was investigated for the first time by degrading a common dye under UV exposure. It was shown that the photocatalytic activity of the nanocomposites was higher compared to either the polymer or TiO₂ alone. A simple mechanism was proposed to explain this observed synergetic effect.     

Charge trapping and storage by composite P3HT/PC60BM nanoparticles investigated by fluorescence-voltage/single particle spectroscopy

Fluorescence-voltage/single particle spectroscopy (F-V/SPS) was employed to study exciton-hole polaron interactions and interfacial charge transfer processes for pure poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) and composite P3HT/PC(60)BM NPs in functioning hole-injection devices. F-V/SPS data collected on a particle-by-particle basis reveal an apparent bistability in the fluorescence-voltage modulation curves for composite NPs of P3HT and [6,6]-phenyl-C(61)-butyric acid methyl ester (PC(60)BM) that is absent for pure P3HT NPs. A pronounced deep trapping of free electrons photogenerated from the composite P3HT/PC(60)BM NPs at the NP/dielectric interface and hole trapping by fullerene anions in composite P3HT/PC(60)BM NPs under photoexcitation lies at the basis of this finding. The deep electron trapping effect reported here for composite conjugated polymer/fullerene NPs presents an opportunity for future application of these NPs in nanoscale memory and imaging devices.