Synthetic Metals (v.160, #13-14)

Poly(3,4-ethylenedioxythiophene) (PEDOT) films, with Cl, NO3 , poly(styrene sulfonate) (PSS) or carbon nanotubes (CNTs) as counter ions, were electrochemically deposited onto indium tin oxide (ITO) glass from aqueous electrolyte. PEDOT film, with tetrafluoroborate anions (BF4 ) as counter ions, was also electrochemically deposited on ITO glass from a propylene carbonate-based electrolyte. The effect of counter ions on the morphology of PEDOT films was demonstrated by the characterizations with scanning electron microscope (SEM). Different carbon-based materials were explored as the substrate materials for PEDOT film generation in electropolymerization, including carbon ink paper, carbon paper, carbon felt, and reticulated vitreous carbon foam (RVC foam). The micro-structure and the surface morphology of the resulted PEDOT films were imaged with SEM. The elemental analysis of the films was performed with energy dispersive X-ray analysis (EDAX). The topography of the PEDOT films was characterized using confocal white light microscopy (COM). A biofuel cell cathode was prepared by immobilization of Trametes Hirsuta laccase (Th-laccase) in PEDOT and the performance of the electrode towards oxygen reduction was examined by chronoamperomentric measurements.
Keywords: Conducting polymer (CP); Poly(3,4-ethylenedioxythiophene) (PEDOT); Micro-structure; Surface morphology;

Tunable photoluminescence of poly(phenylene vinylene) nanofibers by doping of semiconductor quantum dots and polymer by Cheng Wang; Eryun Yan; Guangming Li; Zhiyao Sun; Shuhong Wang; Yanbin Tong; Wenwen Li; Yi Xin; Zonghao Huang; Pengfei Yan (1382-1386).
In this paper, we report the effects of polyvinyl alcohol (PVA) and CdS quantum dots (QDs) on the photoluminescence (PL) properties of poly(phenylene vinylene) (PPV) nanofibers. The composite nanofibers were fabricated by coupling self-assembly and electrospinning method. A significant blue shift in both PL spectra and fluorescence images of PPV fibers was observed after doping of CdS QDs and PVA in succession. It was found that the changes in PL spectra of PPV originated from the chemical interactions between PPV and PVA, and the changes in the crystallization of PPV itself. A possible PL mechanism was proposed accordingly.
Keywords: Nanofibers; QDs; Photoluminescence; Poly(phenylene vinylene); Composite;

Silver wire/polyaniline (Ag0/PAni) composite was prepared by the sonochemical solvent assisted method. This composite was obtained after sonicating a silver nitrate (AgNO3) and anilinium nitrate aqueous solution in the presence of isopropyl alcohol. The presence of the alcohol decreases the polymerization kinetics of the conducting polymer and allows a more stable dispersion of the polymer composite to be obtained. As a matter of fact, precipitation of the polymer occurs when the reaction takes place in the absence of isopropyl alcohol. Scanning electron microscopy revealed that isopropyl alcohol has a remarkable effect on the growth and the morphological structure of reduced silver. Also, the reaction time is an important parameter which allows us to obtain silver wires with a mean diameter of 120 nm and a medium length of 4 μm instead of the spherical particles ordinarily obtained by synthesis without the alcohol. Additionally, we observed that bigger silver wires with a mean diameter of 1.5 μm and a length of 85 μm were obtained if the reaction medium was left to rest in a dark place after the sonication process ended. X-ray diffraction (XRD) and UV–vis absorption spectroscopy indicate that the reduced silver is highly crystalline and the polymer obtained is PAni in the emeraldine salt form.
Keywords: Silver; Polyaniline; Sonochemical method; Nanowires;

Polypyrrole nanowire modified graphite (PPy/G) electrode used in capacitive deionization by Yujie Zhang; Yue Wang; Shichang Xu; Jixiao Wang; Zhi Wang; Shichang Wang (1392-1396).
With high specific capacitance and good conductivity, polypyrrole nanowire modified graphite (PPy/G) electrode has great promising applications in capacitive deionization (CDI). Preparation parameters of modified electrode such as concentration of supporting electrolyte solution (LiClO4), concentration of monomer (pyrrole, Py), pH of polymerization medium, polymerization potential and time have significant effects on the electrode adsorption capacity of NaCl. The experimental results indicate that the optimal preparation condition of the PPy/G electrode used for CDI is 0.10 M LiClO4, 0.19 M Py and pH 5.91 which was controlled by phosphates buffer solution (PBS, 0.10 M), polymerized at 0.85 V vs saturated calomel electrode (SCE) with polymerization time of 150 s. The obtained electrode has an area specific capacitance of 0.188 F/cm2 determined by cyclic voltammetry (CV) method in 1.0 M HClO4 at a scanning rate of 0.05 V/s. In addition, the desalination experiments of the electrode were carried out in 500 ppm NaCl solution at a working voltage of 1.4 V. The experimental results indicate that the NaCl can be removed from the feed solution by electroadsorbing of the electrode with good desalination stability and the electrode can be regenerated efficiently by its electrodesorbing.
Keywords: Conducting polymers; Polypyrrole nanowire; Modified electrode; Capacitive deionization (CDI); Desalination;

Broadly tunable deep blue laser based on a star-shaped oligofluorene truxene by Yue Wang; Georgios Tsiminis; Ying Yang; Arvydas Ruseckas; Alexander L. Kanibolotsky; Igor F. Perepichka; Peter J. Skabara; Graham A. Turnbull; Ifor D.W. Samuel (1397-1400).
We report amplified spontaneous emission (ASE) and optically pumped deep-blue-emitting distributed feedback (DFB) lasers based on a star-shaped oligofluorene truxene molecule. A low ASE threshold of 2.1 kW/cm2 at 439 nm was achieved. The material exhibits a high net gain of 38 cm−1 and also low optical loss coefficient of 3.5 cm−1. Second-order DFB lasers show tuning of the emission wavelength from 422 to 473 nm, and a minimum threshold density of 515 W/cm2. This is the broadest tuning range (51 nm) reported for organic deep-blue/blue lasing materials.
Keywords: Fluorene; Oligomers; Amplified spontaneous emission; Organic semiconductor; Distributed feedback;

With a view to develop conducting polymer film of high electroactivity, pentacyanonitrosylferrate (PCNFe) doped polypyrrole (PPY) composite films are prepared using cyclic voltammetry deposition method. The PPY–PCNFe composite is characterized by FTIR, TEM and TGA analysis. The electroactivity of PPY–PCNFe composite film is studied in 3 mM KCl (common electrolyte) solution. Two redox pairs at E 1/2  = −0.59 V and 0.02 V due to redox behavior of polymer and dopant anions respectively are observed. The electroactivity study reveals the existence of two types of PCNFe dopant anions in the polymeric film: one form is loosely held and prone to easy removal from the polymer matrix whereas the other form is strongly bound to polymer backbone and prone to electrochemical redox reaction by movements of electrons. The high electroactivity of the film is attributed to the movements of ionic species into and out of the polymeric film as well as movements of electron.
Keywords: Polypyrrole; Pentacyanonitrosylferrate; Composite; Deposition; Cyclic voltammetry;

Photolithographic patterning of conducting polyaniline films via flash welding by Rowan D. Henderson; Michael C. Breadmore; Lynn Dennany; Rosanne M. Guijt; Paul R. Haddad; Emily F. Hilder; Peter C. Innis; Trevor W. Lewis; Gordon G. Wallace (1405-1409).
In this work, two significant advances in photolithographic patterning of polyaniline (PANI) films are reported. Firstly, flash welding was enhanced through the use of polymeric substrates, enabling complete penetration of the welding of PANI films with thicknesses ranging from 5 to over 14 μm, significantly thicker than reported previously. Masking of parts of the PANI films during flash welding enabled the formation of adjacent conducting and insulating regions as the welding changes the electrical properties of the film. Raman spectroscopy was used to determine the sharpness of these edges, and indicated that the interface between the flash welded and masked regions of the PANI films was typically less than 15 μm wide. Secondly, using longpass filters, light with a wavelength less than 570 nm was found not to contribute to the welding process. This was confirmed by the use of a 635 nm laser diode for welding the PANI films. This novel approach enabled patterning of PANI films using a direct writing technique with a narrow wavelength light source.
Keywords: Polyaniline; Patterning; Flash welding;

Electrospun poly(vinyl alcohol) nanofibers incorporating PEGylated multi-wall carbon nanotube by Min Jee Kim; Jeongwoo Lee; Dongsoo Jung; Sang Eun Shim (1410-1414).
Recently, the fabrication of polymer composite nanofibers containing multi-wall carbon nanotube (MWCNT) by electrospinning has attracted much attention due to their potential advantages for the enhancement of properties such as electrical and thermal conductivity. In order to utilize the superior properties of MWCNT, in this study, MWCNT was covalently grafted with poly(ethylene glycol) (PEG) chains and PEGylated MWCNT-incorporated PVA nanofibers were prepared by electrospinning. To do so, MWCNT was firstly chemically oxidized to bear carboxyl groups and successively reacted with PEG molecules in ethanol. The PEGylated MWCNT was mixed with aqueous PVA solution and electrospinning was performed. The degree of surface modification of MWCNT by PEG was thoroughly investigated by FT-IR, XPS and TGA. Compared to the pristine MWCNT, the PEGylated MWCNT was uniformly dispersed PVA nanofibers without agglomeration. Because of the enhanced dispersion of PEGylated MWCNT in PVA nanofibers, the electrical conductivity of nanofibers with PEGylated MWCNT (1.0 wt%) was increased by 4 orders of magnitude compared to that of nanofibers with pristine MWCNT (1.0 wt%).
Keywords: Multi-walled carbon nanotubes; Poly(vinyl alcohol); Electrospinning; Electrical conductivity; Nanofibers;

Electrospun PEDOT:PSS/PVP nanofibers as the chemiresistor in chemical vapour sensing by Jaewon Choi; Jeongwoo Lee; Jinsub Choi; Dongsoo Jung; Sang Eun Shim (1415-1421).
Herein, PEDOT:PSS/PVP nanofibers were produced by electrospinning. The presence of PEDOT:PSS in the nanofibers was confirmed by FT-Raman spectroscopy. The applied voltage-dependent diameter of PEDOT:PSS/PVP nanofibers was observed. Also, sensing behaviors of electrospun PEDOT:PSS/PVP nanofibers were explored by measuring its response upon cyclic exposure to organic vapours such as ethanol, methanol, THF, and acetone at room temperature. When PEDOT:PSS/PVP nanofibers were exposed to each solvent, the protic and aprotic solvents resulted in opposite electrical responses. These findings exhibit that electrospun PEDOT:PSS/PVP nanofibers are the promising candidate for the organic vapour sensing material.
Keywords: Chemical vapour sensor; PEDOT:PSS; PVP; Electrospinning; Nanofiber;

Frequency dependent electrical transport properties of 4,4′,4″-tris(N-3-methylphenyl-N-phenylamine)triphenylamine by impedance spectroscopy by Gayatri Chauhan; Ritu Srivastava; Priyanka Tyagi; Amit Kumar; P.C. Srivastava; M.N. Kamalasanan (1422-1426).
The frequency dependent ac conduction mechanism in 4,4′,4″-tris(N-3-methylphenyl-N-phenylamine)triphenylamine (m-MTDATA) has been studied as a function of applied bias and temperature. The Cole–Cole plot shows a slightly depressed semicircle indicating Debye type relaxation. This result has been explained by an equivalent circuit of the device designed as a two parallel resistor and capacitance network in series with contact resistance. The ac conduction studies under dc bias for hole only devices shows an increase in device conductivity with the increase in bias. The variation of bulk resistance with applied bias indicates Space Charge Limited Conduction (SCLC) mechanism for hole conduction. The hole mobility of the material has also been evaluated from SCLC as 8.859 × 10−6  cm2/V s. The temperature dependent impedance studies show two activation energies indicating two different phase of the material with a phase transition at 235 K.
Keywords: Charge transport; SCLC; Mobility; Phase transition;

An alternating phenylenevinylene copolymer P with perylene bisimide units has been used as organic sensitizer to fabricate dye-sensitized solar cells (DSSCs) based on porous and TiCl4 modified TiO2 photoelectrodes. As a consequence of the compact layer formed by TiCl4 treatment to the porous TiO2 thin film layer, an efficient electron network was formed. Dark current measurements and electrochemical impedance spectra (EIS) suggested that modified photoelectrode significantly reduced the recombination rate of electrons with redox couple in the electrolyte due to the reduced bare FTO surface and longer electron lifetime as compared to the porous TiO2 photoelectrode. The power conversion efficiency of DSSCs utilizing this copolymer as sensitizer is about 2.60% and 3.98% with porous and modified TiO2 photoelectrodes, respectively.
Keywords: Modified TiO2 photoelectrode; Compact layer; Dye-sensitized solar cells (DSSCs); Electron lifetime; Recombination rate;

Facile one-step route to polyaniline–silver nanocomposite particles and their application as a colored particulate emulsifier by Syuji Fujii; Yukihiro Nishimura; Atsushi Aichi; Soichiro Matsuzawa; Yoshinobu Nakamura; Kensuke Akamatsu; Hidemi Nawafune (1433-1437).
Polyaniline–silver nanocomposites were synthesized in the form of colloidal particles by the facile one-step aqueous chemical oxidative dispersion polymerization of aniline using silver nitrate as an oxidant and poly(vinyl alcohol) as a colloidal stabilizer. Aniline monomer was oxidized by silver ions, yielding polyaniline and elemental Ag simultaneously. The synthesized nanocomposite particles were colloidally stable over 2 years and transmission electron microscopy studies indicated the production of spherical, plate and rod-shaped polyaniline–silver nanocomposite particles with a silver core–polyaniline shell morphology. The conductivity of a pressed pellet of the nanocomposite particles using the conventional four-point probe technique was 1.4 × 10−2  S/cm at 25 °C. The nanocomposite particles behaved as a ‘colored’ particulate emulsifier for the stabilization of transparent oil-in-water emulsions.
Keywords: Polyaniline; Nanocomposite; Colloid; Aqueous chemical oxidative polymerization; Pickering emulsion;

A novel low band gap conjugated polymer based on N-substituted dithieno[3,2-b:2′,3′-d]pyrrole by Yong Lu; Hui Chen; Xiaoya Hou; Xiao Hu; Siu-Choon Ng (1438-1441).
Poly{[N-dodecyl-dithieno(3,2-b:2′,3′-d)pyrrole-2,6-diyl]-alt-[2,1,3-benzothiadiazole-4,7-diyl]} (PBTDTP) was successfully prepared via Stille coupling. The new polymer is soluble in common organic solvents such as chloroform (CHCl3), tetrahydrofuran (THF) and o-dichlorobenzene. Compared with N-alkyl dithieno[3,2-b:2′,3′-d]pyrrole (DTP) homopolymer, the maximum absorption of PBTDTP was red-shifted approximately 40 nm. The optical band gap of the polymer in film state is 1.55 eV calculated from the onset of absorption spectrum. The cyclic voltammetry measurements of the polymer depicted a HOMO energy level of −5.0 eV and a LUMO energy level of −3.3 eV of PBTDTP. This work demonstrates that this newly synthesized polymer is a promising p-type material for application in bulk hetero-junction organic solar cells.
Keywords: Conjugated polymers; Low band gap; Donor–acceptor copolymer; Electrochemistry; Fused ring;

The grafting of polypyrrole onto the surface of modified silica nanoparticles has been investigated. These silica nanoparticles were modified with pyrrole moieties prepared by the well-known Stober method in one-step starting from TEOS and a pyrrole-bearing trialkoxysilane compound. The effects of various reaction conditions, including reaction time, solvent, and molar ratio of water to alkoxy groups, have been investigated in order to obtain pyrrole-modified silica nanoparticles with the optimal core–shell structure and the smallest possible particle size. The grafting was carried out in aqueous FeCl3 solution containing the modified silica nanoparticles, with pyrrole monomers already adsorbed on the surface of the particles by soaking. Several analytical tools have been employed to characterize the particles and to assess the degree of grafting, namely TEM, SEM, TGA, FTIR, and XPS. The final polypyrrole-grafted silica nanoparticles obtained had a mean diameter of about 220 nm and 50 wt.% of grafted polypyrrole with respect to the total weight of polypyrrole formed around the surface of the cores.
Keywords: Grafting; Modification; Nanoparticles; Polypyrrole; Silica;

A novel series of metallic (Al, Zn) centered inorganic Si–O network/polymer hybrid materials have been constructed. Among functional linkage HQSi is achieved from the modification of 8-hydroxyquinoline (HQ) by 3-(triethoxysilyl)-propyl isocyanate (TESPIC) and used to covalently bonding Si–O network. Poly-(methyl methacrylate) (PMMA) or poly-(methacrylic acid) (PMAA) is introduced by the polymerization of methyl methacrylate (MMA) or methacrylic acid (MAA), respectively. Both inorganic Si–O network and polymer chain are coordinated to some metal ions (Al3+, Zn2+), resulting in the ternary luminescent hybrid material systems (abbreviated as HQ–Si–M–PMMA(PMAA), M = Al, Zn). The physical characterization and especially the photoluminescence property of them are studied in detail, which present the regular microstructure and green photoluminescence originated from the photoactive modified HQ functional unit by the perturbation of metallic ions (Al3+, Zn2+).
Keywords: Inorganic/polymeric hybrid material; Photoluminescence; 8-Hydroxyquinoline derivative; Aluminum ion; Zinc ion;

A particularly strong organic acceptor for tuning the hole-injection barriers in modern organic devices by Gerold M. Rangger; Oliver T. Hofmann; Benjamin Bröker; Egbert Zojer (1456-1462).
A better understanding of metal-organic interfaces combined with means to control their properties is crucial for the further improvement of organic (opto)electronic devices. In this context, the use of organic acceptors is an efficient tool to modify metal work functions and hole-injection barriers, which has the potential to considerably improve the performance of organic devices. Here, we use density functional theory based calculations to discuss a particularly potent acceptor suitable for that purpose, 3,5-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane (F2HCNQ), which clearly outperforms the frequently applied and in the meantime prototypical system 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Comparative calculations for a single monolayer of the two molecules adsorbed on an Ag(1 1 1) surface reveal that (i) the work-function increase induced by F2HCNQ is more than 20% higher than for F4TCNQ and that (ii) at the same time the adsorption energy basically is unaffected, while (iii) the electronic structure is slightly modified. In the end of the day, F2HCNQ is a highly promising candidate for applications in organic devices.
Keywords: Organic electronics; Interfaces; Quantum-mechanical modeling; Band-structure calculation; Work-function modification;

Self-assembled polyaniline 12-tungstophosphate micro/nanostructures by Gordana Ćirić-Marjanović; Ivanka Holclajtner-Antunović; Slavko Mentus; Danica Bajuk-Bogdanović; Dragana Ješić; Dragan Manojlović; Snežana Trifunović; Jaroslav Stejskal (1463-1473).
Polyaniline (PANI) micro/nanostructures were synthesized by the external-template-free oxidative polymerization of aniline in aqueous solution of 12-tungstophosphoric acid (WPA), using ammonium peroxydisulfate (APS) as an oxidant and starting the oxidation of aniline from slightly acidic media (pH 5.4–5.9). The effect of the initial weight ratio of WPA to aniline on molecular structure, morphology, and physicochemical properties of polyaniline 12-tungstophosphate (PANI-WPA) was investigated by FTIR, Raman and inductively coupled plasma optical emission (ICP-OES) spectroscopies, elemental analysis, X-ray powder diffraction (XRPD), scanning and transmission electron microscopies (SEM and TEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and conductivity measurements. The morphological change of polymerization products during a single polymerization process, from non-conducting submicro-/microspherical oligoaniline intermediates to semiconducting PANI-WPA consisted of self-assembled nanotubes and/or nanorods co-existing with submicro-/microspheres, has been revealed by SEM and TEM. The average diameter of nanorods in PANI-WPA samples decreased with increasing the initial WPA/aniline weight ratio. The incorporation of 12-tungstophosphate counter-ions into PANI matrix has been proved by FTIR, Raman and ICP-OES spectroscopies, TGA and DTA analysis. Electrical conductivity of PANI-WPA increased in the range (2.5–5.3) × 10−3  S cm−1 with the increase of the initial WPA/aniline weight ratio. The presence of branched structures and phenazine units besides the ordinary paramagnetic and diamagnetic emeraldine salt structural features in PANI-WPA was proved by FTIR and Raman spectroscopies.
Keywords: Polyaniline; 12-Tungstophosphoric acid; Nanorods; Nanotubes; Submicrospheres; Microspheres;

Organic field-effect transistors using liquid crystalline compound synthesized to enhance carrier-transport ability by Norio Onojima; Iki Shintani; Shin-ichi Kitahara; Tsutomu Takahashi; Takamasa Kato; Yuichiro Haramoto (1474-1478).
We report the characteristics of organic field-effect transistors (OFETs) using the liquid crystalline compound synthesized to enhance carrier-transport ability. Oblique evaporation with a tilt angle of 60° and subsequent thermal annealing at 200 °C yielded anisotropic carrier transport due to the anisotropic molecular alignment. The OFETs fabricated with polymethylmethacrylate (PMMA) intermediate layers showed mobility up to 2.6 × 10−2  cm2/V s. The characteristics of OFETs depended on the deposition rate of liquid crystalline materials. The mobilities increased with decrease in the deposition rate. Polarization-resolved photoluminescence (PL) measurements exhibited that the molecular orientation in liquid crystalline films was improved with decrease in the deposition rate. Therefore it is assumed that the carrier-transport properties were enhanced by improving the molecular orientation in the liquid crystalline films.
Keywords: Organic field-effect transistor; Liquid crystalline compound; Oblique evaporation; Polarization-resolved photoluminescence;

Polyaniline (PANI) reduces silver nitrate to metallic silver. Composites based on conducting polymer and silver have been prepared with equimolar proportions of reactants. Polyaniline bases having different morphologies – granular or nanotubular – and oligoaniline microspheres have been left to react with silver nitrate in acidic, neutral, and alkaline media. The content of silver, typically 20–30 wt.%, was determined by thermogravimetric analysis. Clusters of 40–80 nm silver particles are produced in the granular form of PANI. The formation of silver inside PANI nanotubes has been observed. With oligoaniline microspheres, silver was produced on their surface, and on PANI agglomerates accompanying them. The highest conductivity, 943 S cm−1, was found with silver reduced by nanotubular PANI base in 0.1 M nitric acid at 17.3 wt.% silver content. The standard granular PANI, used as a reference material, yielded a composite having a much lower conductivity of 8.3 × 10−5  S cm−1 at 24.3 wt.% Ag. There is no simple correlation between the conductivity and silver content. Infrared and Raman spectroscopies have been used to study the changes in the molecular structure of the PANI bases of various morphologies before and after reaction with silver nitrate.
Keywords: Aniline oligomers; Conducting polymer; Nanotubes; Polyaniline; Silver;

Fabrication and characterization of Schottky diodes and thin films based on poly(o-toluidine) deposited by spincoating technique by A. Elmansouri; A. Outzourhit; A. Oueriagli; A. Lachkar; N. Hadik; M.E. Achour; A. Abouelaoualim; A. Malaoui; K. Berrada; E.L. Ameziane (1487-1492).
Poly(o-toluidine) (POT) thin films were fabricated by spin coating on bare glass and indium–tin–oxide (ITO)-coated glass substrates, from a solution of poly(o-toluidine) in chloroform. The optical transmittance of the as-deposited and doped films was measured in the 250–1200 nm wavelength range. These measurements showed that the optical band gaps of the undoped and doped polymer films are on the order of 3.28 and 2.7 eV, respectively, and that doping increases absorption in the near infrared region. The FT-Raman measurement on spincoated POT film is comparable to that of polyaniline. The electrochemical properties of those thin films are presented using cyclic voltammetry. ITO/POT/Al devices were fabricated by thermal evaporation of aluminum circular contacts on films deposited on ITO-coated glass. The current–voltage characteristics of the devices indicate a Schottky diode-type behavior. The current–voltage characteristics can be fitted using the modified Shockley equation. The diode parameters were calculated from IV characteristics and discussed. On the other hand, capacitance of these structures decreased with increasing frequency.
Keywords: Schottky diode; Poly(o-toluidine); Spincoating; Electrical properties;

Manufacture of brightness enhancement films (BEFs) by ultraviolet (UV) irradiation and their applications for organic light emitting diodes (OLEDs) by Jian-Shian Lin; Shih-Hsun Lin; Nien-Po Chen; Cheng-Hao Ko; Zong-Sian Tsai; Fuh-Shyang Juang; Chen-Ming Chen; Lung-Chang Liu (1493-1500).
By ultraviolet (UV) irradiation, brightness enhancement films (BEFs) have been successfully manufactured with UV-curable polymers and applied for organic light emitting diodes (OLEDs).With BEFs, either green OLEDs (BEF/ITO glass/NPB (30 nm)/Alq3 (65 nm)/LiF (0.5 nm)/Al (100 nm)) or white OLEDs (BEF/ITO glass/TAPC (40 nm)/mCP:Os:Firpic mixture (weight ratio = 82:17:1; 25 nm)/BCP (15 nm)/Alq3 (30 nm)/LiF (0.5 nm)/Al(150 nm)) exhibit better electroluminescent performances than those without BEFs. In case of green OLEDs, the luminance and electroluminescent yield with 45° compound BEFs are, respectively, 1.51-fold and 1.42-fold (at 9 V, 60 mA/cm2) larger than those without BEFs. In case of white OLEDs, moreover, the luminance and electroluminescent yield with 45° compound BEFs are, respectively, 1.28-fold and 1.21-fold (at 9 V, 16 mA/cm2) larger than those without BEFs.
Keywords: OLED; Brightness enhancement film; Ultraviolet;

Study of the effect of DMSO concentration on the thickness of the PSS insulating barrier in PEDOT:PSS thin films by I. Cruz-Cruz; M. Reyes-Reyes; M.A. Aguilar-Frutis; A.G. Rodriguez; R. López-Sandoval (1501-1506).
One of the most used secondary dopants in thin film processing of PEDOT:PSS is dimethyl sulfoxide (DMSO). In this work, we present results that explain, from the point of view of impedance spectroscopy, the mechanism of the increase in the conductivity observed on films based on PEDOT:PSS. The results obtained with this technique, combined with others such as AFM, and Raman and UV–vis–NIR spectroscopies, clearly show that there is a thinning of the insulating barrier of PSS surrounding conductive grains of PEDOT. It is shown that the thickness of the insulating barrier is related strongly and inversely with the onset frequency of AC conductivity. However, this is not the only existing effect, because for values beyond the optimal concentration of DMSO, we observe a decrease in the conductivity related with an increase of the separation of the PEDOT grains. The AC measurements and the AFM images also show the clear interplay between the increase of the PEDOT average grain size and the separation between them.
Keywords: PEDOT; Impedance spectroscopy; DMSO;

Fabrication and characterization of polyaniline/porous silicon heterojunction by Pawan Kumar; Sarbani Adhikari; P. Banerji (1507-1512).
Heterojunction between polyaniline (PANI) and porous silicon (PS) was fabricated by making a layer of PANI on PS, using spin coating method. PS was fabricated by electrochemical etching process. PS was characterized by photoluminescence (PL), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) while the PANI was characterized by FTIR and absorption (UV–VIS) spectroscopy. Current–voltage and capacitance–voltage measurements were done to determine the electrical properties of the heterojunction structure. The ideality factor of the heterojunction was found to be 4.2, which was considered high due to large defect density at the interface. Built-in potential was measured by both IV and CV and was found to be Φ b(IV)  = 0.41 V and Φ b(CV)  = 0.28 V respectively. The discrepancy in the values of the built-in potential was discussed. Band discontinuity in conduction band and valence band were found to be 0.65 and 1.27 eV respectively. Solar response of the heterojunction was also observed at AM (air mass) 1.0 and it showed a promising behavior as a photovoltaic device.
Keywords: Polyaniline; Porous silicon; Heterojunction; Current–voltage; Solar response;

The electrical structure of the Al/Al2O3/PPy-NDSA/Au has been investigated by means of current–voltage (IV) and capacitance–voltage (CV) measurements, in a temperature range of 90–350 K. The forward CV measurements have been carried out in the range of frequency of 1 kHz to 20 MHz. The effects of series resistance, interfacial layer and interface states on IV and CV characteristics are investigated. At high current densities in the forward direction, the series resistance effect has been observed for voltages greater than 0.7 V. The analysis of IV characteristics based on the thermionic emission mechanism has been explained by the assumption of a Gaussian distribution of barrier heights, due to barrier height inhomogeneities that prevail at the interface. It has been observed that the forward CV plot exhibits a peak, whose position shifts towards lower voltages and that decreases with increasing frequency. The non-linearity of 1/C 2 versus V plot at high frequency was explained with the assumption that only some of the interface states follow the applied ac signal. Surface analysis by X-ray photoelectron spectroscopy (XPS) was performed in order to evaluate the chemical states of the constituents of the Al/Al2O3/PPy-NDSA/Au sample.
Keywords: Conducting polymer; Schottky barrier; Current–voltage; Electrical properties; Characteristics;

Improved mobility of the copper phthalocyanine thin-film transistor by Fahrettin Yakuphanoglu; Mujdat Caglar; Yasemin Caglar; Saliha Ilican (1520-1523).
Copper phthalocyanine (CuPc) organic thin-film transistor (OTFT) was fabricated by thermal evaporation deposition on p-SiO2 dielectric layer. Organic thin-film transistors used in large display areas need the enhancement of transistor performances by increasing the I on/I off ratio and the mobility. The output and transfer characteristics of CuPc-OTFT having source/drain interdigitated-finger geometry were investigated. The mobility, I on/I off ratio and inverse sub-threshold slope for the CuPc-OTFT were found to be 5.32 × 10−3  cm2  V−1  s−1, 1.94 × 104 and 2.5 V/decade, respectively. The interface state density of the transistor was found to be 3.73 × 1011  eV−1  cm−2 using the conductance-frequency method. The CuPc film indicated a homogeneous surface having 3.878 nm small roughness values as observed by atomic force microscope (AFM) measurements. The obtained results indicate that we have improved a CuPc-OTFT transistor with high mobility without being of any substrate treatment.
Keywords: Organic thin-film transistor; Copper phthalocyanine; Thermal evaporation;

Induced doping by sodium ion in poly(m-aminophenol) through the functional groups by Pradip Kar; Narayan C. Pradhan; Basudam Adhikari (1524-1529).
Poly(m-aminophenol) (PmAP) was synthesized by the oxidative polymerization of m-aminophenol in sodium hydroxide medium using ammonium persulfate oxidant at room temperature. The synthesized polymer showed very good solution processability as it was well soluble in aqueous sodium hydroxide, dimethylsulfoxide (DMSO), dymethylformamide (DMF), etc. A free-standing film was cast from thermal evaporation of DMSO solution of the synthesized PmAP. The film was then doped with aqueous sodium hydroxide and methanol mixture by solution doping technique at room temperature. The doping conditions were standardized in terms of the DC-conductivity of the doped film. The doped PmAP was characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, Electron dispersion spectroscopy, X-ray diffraction spectroscopy, elemental analysis by atomic absorption spectroscopy, thermogravimetric analysis and DC-electrical conductivity. The DC-electrical conductivity of PmAP film was increased to 2.34 × 10−5  S/cm from <10−12  S/cm due to sodium ion doping. From all the above characterizations it was confirmed that the sodium ions were not the reason for the conduction. The incorporated sodium cation in the polymer through free –OH groups of the polymer chain was induced the electron cloud of the polymer and so the polymer became conducting.
Keywords: Poly(m-aminophenol); Thin film; Organic semiconductors; Induced doping; Conducting polymer;

Electrical, optical and hole transport mechanism in thin films of poly(3-octylthiophene-co-3-hexylthiophene): Synthesis and characterization by Mohd Taukeer Khan; Manisha Bajpai; Amarjeet Kaur; S.K. Dhawan; Suresh Chand (1530-1534).
The present study demonstrates the designing of copolymer poly(3-octylthiophene-co-3-hexylthiophene) (P3OT-HT) and study of the hole transport mechanism in it. Detailed structural, optical and thermal studies of P3OT-HT discuss its synthesis aspects. Current density–voltage characteristics have been studied at different temperatures (290–110 K) to understand the mechanism of hole transport in P3OT-HT. It has been established that current density in P3OT-HT thin films is governed by space charge limited conduction with traps distributed exponentially in energy and space. Hole mobility is both temperature and electric field dependent arising due to substituent functional groups attached the polymer backbone.
Keywords: Hole transport; Mobility; Space charge limited current; P3OT-HT;

Synthesis, crystal structure and two-photon absorption of a cadmium complex constructed by DMIT ligand by Ting Bin Li; Quan Ren; Ya Li Hu; Chun Lin Ma; Guo Bing Zheng; Dong Xu (1535-1538).
The cadmium complex [(CH3)4N][Cd(C3S5)2]·H2O constructed by 1,3-dithiole-2-thione-4,5-dithiolato (DMIT) ligand has been synthesized and its structure has been determined by means of X-ray single crystal diffraction. Its two-photon absorption (TPA) has been studied in acetonitrile solution using open-aperture Z-scan technique with 20 picosecond (ps) pulses at wavelength 1064 nm. Its TPA coefficient β was determined to be 4.475 × 10−10  m/W, corresponding the TPA cross-section σ 2 is 3.95 × 10−53 (m4  s/photon molecule).
Keywords: Cadmium complex; Crystal structure; Two-photon absorption; Z-scan;

Cationic and radical polymerization of N-vinyl-2-phenylpyrrole: Synthesis of electroconducting, paramagnetic and fluorescent oligomers by Boris A. Trofimov; Marina V. Markova; Lyudmila V. Morozova; Al’bina I. Mikhaleva; Lyubov’ N. Sobenina; Ol’ga V. Petrova; Tamara I. Vakul'skaya; Galina F. Myachina; Konstantin B. Petrushenko (1539-1543).
Cationic polymerization of N-vinyl-2-phenylpyrrole (catalysts: Me3SiCl, CF3COOH, BF3·OEt2, HCl, WCl6, FeCl3, complex LiBF4–dimethoxyethane, catalysts concentration 1–2 wt%, 20–70 °C, 24–48 h) affords oligomers (molecular weight 1400–1700) of a unexpected structure with alternating 2-phenylpyrrole and ethylydene units, the yields reaching 63%. The oligomers structure has been supported by isolation and identification of the corresponding dimer, N-vinyl-2-phenyl-5-[N-(2-phenyl-1H-pyrrol-1-yl)ethyl]-1H-pyrrole. Radical polymerization of the same monomer (AIBN, 1.5–4 wt%, 60–80 °C, 40–60 h or UV irradiation or both) gives oligomers (molecular weight 2100–3000) of normal structure having polyethene backbone with pendant 2-phenylpyrrole groups in up to 40% yields. The oligomers of both types are semiconductors (1.3 × 10−6–3.6 × 10−6  S/cm) after doping with I2, paramagnetic (4.2 × 1017–8.7 × 1017  g−1) and fluorescent in a near UV region (λ 355–363 nm, acetonitrile).
Keywords: N-Vinyl-2-phenylpyrrole; Cationic polymerization; Radical polymerization; Conducting oligomers; Fluorescent oligomers;

Synthesis and characterization of red-emitting diketopyrrolopyrrole-alt-phenylenevinylene polymers by Zhi Qiao; Yanbin Xu; Shuimu Lin; Junbiao Peng; Derong Cao (1544-1550).
Two novel diketopyrrolopyrrole (DPP) and p-phenylenevinylene alternating copolymers, poly(1,4-(2,5-dicyano)-phenylenevinylene-alt-2,5-dioctyl-3,6-bis(4-vinylenephenyl)pyrrolo[3,4-c]pyrrole-1,4-dione) (P1) and poly(1,4-(2,5-diethoxy)-phenylenevinylene-alt-2,5-dioctyl-3,6-bis(4-vinylenephenyl)pyrrolo[3,4-c]pyrrole-1,4-dione) (P2), were synthesized through Wittig reaction in good yields, and were characterized by FTIR, NMR. Two polymers possessed moderate molecular weights and polydispersities, well-defined structures, and were readily soluble in common organic solvents. In particular, P1 and P2 exhibited excellent thermal stability with T d  = 393 and 398 °C at 5% weight loss, respectively. Both P1 and P2 in solution and in thin films exhibited strong red photoluminescence. Both electroluminescence devices using ITO/PEDOT/polymer/Ba/Al configuration with P1 and P2 as the emitting layer showed nearly pure red emission with the emission peaks at 646 nm for P1 and 648 nm for P2, and exhibited low turn-on voltages of 4.5 and 3.4 V, respectively. The results show that P1 and P2 are promising candidates for red emissive materials in polymer light-emitting diodes.
Keywords: Light-emitting; Polymer light-emitting diodes; Diketopyrrolopyrrole; Wittig reaction;

Electrical and photovoltaic properties of a metal–semiconductor–insulator–polymer–metal diode were investigated. The n-Si/SiO2/MEH-PPV/Al diode shows a rectifying behavior with the rectification ratio of 2.22 × 105 at ±5 V and exhibits a non-ideal behavior due to the series resistance and oxide-organic layers. The organic semiconductor makes a contribution to the IV characteristics of the diode and the trap-charge limited space charge and space charge limited current mechanisms were observed for the diode. The current–voltage characteristics of the n-Si/SiO2/MEH-PPV/Al diode under different illumination intensities give an open circuit voltage (V oc) along with a short circuit current (I sc). This suggests that the n-Si/SiO2/MEH-PPV/Al diode is a photovoltaic device with V oc  = 0.456 V and J sc  = 7.89 × 10−8  A/cm2 values under 100 mW/cm2 illumination intensity. The photoconductivity mechanism of the diode is controlled by monomolecular recombination. The interface state density D it values with time constant τ it of the diode under dark and illumination conditions were found to be 2.53 × 1010  eV−1  cm−2 with 5.09 × 10−5  s and 2.50 × 1010  eV−1  cm−2 with 8.27 × 10−5  s, respectively. The obtained results indicate that the n-Si/SiO2/MEH-PPV/Al diode is a photo-sensitive diode.
Keywords: Metal–oxide–semiconductor contact; Light sensitive capacitor; Organic semiconductor;

In this study, a novel ligand, 7-(2,3-dicyanophenoxy)-3-(2-chloro-4-fluorophenyl)coumarin was synthesized by the reaction of 3-(2-chloro-4-fluorophenyl)-7-hydroxycoumarin with 1,2-dicyano-3-nitrobenzen in dry DMF as the solvent in the presence of K2CO3 as the base. The preparation of the corresponding phthalocyanines H2Pc, CoPc and ZnPc, substituted with 7-oxo-3-(2-chloro-4-fluorophenyl)coumarin functional groups at α positions of the Pc ring, was achieved by the cyclotetramerization of the coumarin ligand without any metal salts or with the relevant metal(II) acetates in 2-N,N-dimethylaminoethanol. The structures of the compounds were confirmed by elemental analysis, UV–vis, IR, MALDI-TOF mass and 1H NMR spectra. In addition, aggregation and redox properties of the novel phthalocyanines with four halogenated coumarinoxy substituents at α positions of the phthalocyanine ring were compared with those of previously reported corresponding ones with β-substitution, by UV–vis spectroscopy, in situ spectroelectrochemistry and voltammetry. Remarkable differences in these properties between α- and β-substituted compounds were detected, and discussed in detail.
Keywords: Phthalocyanines; Coumarin; α-Substitution; Spectroelectrochemistry;

Polyaniline–silver nanocomposite has been synthesized successfully by the chemical oxidative polymerization of aniline with ammonium peroxydisulphate as an initiator in presence of negatively charged silver nanoparticles. Silver nanoparticles are prepared by standard citrate reduction method. TEM, SEM, XRD, FTIR, TGA, DSC, optical absorption and photoluminescence studies are done for the morphological, structural, thermal and optical characterization of the polyaniline nanocomposite. From the TEM and SEM image, it is observed that nanoparticles are well dispersed in the polyaniline matrix. XRD pattern shows that polyaniline is amorphous, but peaks present in XRD pattern in polymer nanocomposites are for silver nanoparticles. TGA and DSC results show that polyaniline silver nanocomposite is more crystalline and more thermally stable. A surface plasmon absorption band is obtained from the optical absorption at 380 nm, which indicates that silver nanoparticles are present in the polyaniline matrix. The optical band gap of nanocomposite decreases with increasing content of silver nanoparticles. An enhancement in photoluminescence has been observed in polyaniline–silver nanocomposite than that in pure polyaniline. The electrical conductivity of polyaniline–silver nanocomposite increases with increase in silver nanoparticle content than that of pure polyaniline. This is a simple way by which optical and electrical properties of polyaniline may be enhanced by doping with suitable nanoparticles.
Keywords: Polyaniline; Silver nanoparticle; Plasmon absorption; Photoluminescence; Electrical conductivity;

Electron trapping behavior at the interface between N,N′-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13) film and thermal SiO2 was investigated by utilizing ultrathin poly(methyl methacrylate) (PMMA) gate passivation layers. From the capacitance–voltage analysis for the PTCDI-C13/PMMA/SiO2 interface, it is found that the electron tunneling appeared with PMMA thinner than 0.8 nm, and that the thickness of the gate passivation layer should be at least 1 nm for preventing injection-type hysteresis in the capacitance–voltage curve. The effective electron mobility of organic thin-film transistors (OTFTs) based on PTCDI-C13 with SiO2 gate insulator was increased by suppressing shallow-level interface traps on SiO2 with the PMMA layer, which can be partially accounted for by the multiple trap and release model. In this work, the thickness and the density of the PMMA layers were precisely controlled with a simple spin-coating process. Even 1.3-nm thick PMMA layer caused the improvements of the electron mobility and the air stability of the n-channel conduction.
Keywords: Gate passivation layer; Electron trap; n-Channel operation; Organic thin-film transistor; Air stability;

Polyaniline nanofibres have been prepared without any template or surfactant. Although the morphology of polyaniline is well kept after dealing with aqueous ammonia, de-doped polyaniline nanofibres with micropores are of better electrochemical capacitor performances in 1 M H2SO4 aqueous solution. Its specific capacitance is 593 F g−1 at a constant current density of 2.5 A g−1, and can be subjected to charge/discharge over 5000 cycles in the voltage range of 0–0.65 V. Moreover, its capacitance retention ratio reaches circa 87% with the current densities increasing from 2.5 A g−1 to 15 A g−1.
Keywords: De-doped polyaniline; Nanofibre; Electrochemical capacitor;

Third-order optical nonlinear studies of Cobalt (II) Schiff base complex bearing triphenylphosphine using Differential Optical Kerr Gate and Z-scan studies by Bada Jayappa Rudresha; Badekai Ramachandra Bhat; Dileep Ramakrishna; John Kiran Anthony; Fabian Rotermund (1584-1586).
The third-order optical nonlinearity of the composite film of coordination complex [CoLPPh3Cl] (L = N-(2-pyridyl)-N′-(salicylidene)hydrazine) and PMMA has been investigated by using Differential Optical Kerr Gate (DOKG) and Z-scan measurements. Large value of the third-order nonlinear optical susceptibility (χ (3)) of the order of 10−10  esu was measured and its nonlinear response time was found to be faster than or comparable to the laser pulse width (90 fs) used. The single beam Z-scan technique was used to investigate the nonlinear absorption property of the composite near 800 nm. The sample exhibit saturable absorption. The nonlinear absorption coefficient of sample is found to be −32 cm/GW.
Keywords: Optical nonlinearity; Cobalt (II)-Schiff base; Optical Kerr Gate; Z-scan;

Effect of SPFGraphene dopant in MEH–PPV organic light-emitting devices by Zhiyong Liu; Dawei He; Yongsheng Wang; Hongpeng Wu; Jigang Wang (1587-1589).
In this paper, graphene acts as the acceptor material in the luminous layer. The doping behavior of graphene in MEH–PPV has improved the device performance due to the efficient electron injection and transport through highly conductive graphene. When the graphene content is 0.02 wt%, the highest EL brightness reaches 1960 cd/m2 and the threshold voltage declines from 8 V to 5 V. When the graphene content is 0.02 wt%, the device has the highest EL brightness compared with the devices of other graphene content at the same current density. The doping graphene into MEH–PPV results in the best luminous efficiency and balanced electron and hole mobilities in the active layer.
Keywords: SPFGraphene; Energy transfer; MEH–PPV;