Synthetic Metals (v.161, #5-6)
Synthesis, structure and conductivity of molecular conductor β-(BEDT-TTF)(HSO4)
by Hong-Yu Chen; Qi Fang; Ping Li; Wen-Tao Yu; Cui-Ying Xu; Jin-Biao Zhang; De-Qing Zhang (pp. 365-368).
A new BEDT-TTF-based radical salt, β-(BEDT-TTF)(HSO4) [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene], has been synthesized by oxidative electrocrystallization. The crystal structure was determined by four-circle X-ray diffraction. The crystal belongs to monoclinic system, C2/c space group with the unit cell parameters of: a=1.5996(2)nm, b=1.06173(10)nm, c=1.15083(11)nm, β=120.534(8)°, V=1.6834(3)nm3, and R=0.0611. In the title crystal, the BEDT-TTF radicals are stacked to form columns along the  axis and the molecular planes of BEDT-TTFs in adjacent columns are parallel to each other. The inter-stack side-by-side S…S short contacts along the b-axis help to form a kind of cationic conducting sheet parallel to (101) plane. The room temperature conductivity at certain direction on (101) plane of β-(BEDT-TTF)(HSO4) single crystal was measured to be 11.7Scm−1. From 100K to 290K, the resistivity–temperature curve demonstrates its typical semiconductivity with an excitation energy of 0.26eV.
Keywords: Molecular conductor; BEDT-TTF; Conductivity; Structure; Charge-transfer salts
Studies on the fluorescence properties of conjugated polymer poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene in presence of nitrogen dioxide gas
by Kanchan Saxena; Pramod Kumar; V.K. Jain (pp. 369-372).
▶ The fluorescence of MDMO-PPV polymer is quenched in the presence of NO2 gas. ▶ Orange fluorescence of the polymer changes to pale yellow in presence of NO2. ▶ Fluorescence quenching is studied by absorption and emission spectroscopy. ▶ Thin film of polymer may be used as disposable film for detection of NO2 gas.The fluorescence properties of conjugated polymer poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene (MDMO-PPV) has been studied in the presence of nitrogen dioxide gas. It was observed that the fluorescence of MDMO-PPV polymer is quenched in the presence of NO2 gas and the bright orange fluorescence of the polymer changes to pale yellow. The quenching of the fluorescence of the detecting film after exposure to NO2 is also studied by absorption and emission spectroscopy. A thin film of MDMO-PPV polymer deposited on glass substrate, flexible PET film or filter paper may be used as disposable film for detection of NO2 gas.
Keywords: Polymer thin film; Fluorescence quenching; MDMO-PPV
Novel non-covalent sulfonated multiwalled carbon nanotubes from p-toluenesulfonic acid/glucose doped polypyrrole for electrochemical capacitors
by Qingbin Fu; Bo Gao; Hui Dou; Liang Hao; Xiangjun Lu; Kang Sun; Jianchun Jiang; Xiaogang Zhang (pp. 373-378).
► A novel non-covalent method to sulfonate multiwalled carbon nanotubes (MWCNTs) and efficiently improve the dispersibility of MWCNTs. ► The sulfonated MWCNTs used to prepare the composite with polypyrrole for electrochemical capacitors. ► The composite electrode showed superior electrochemical cyclability.A novel and facile non-covalent process was applied to sulfonate multiwalled carbon nanotubes (MWCNTs) with a high –SO3H loading carbonaceous (C-SO3H). Then the sulfonated multi-walled carbon nanotubes/polypyrrole nanocomposite (MWCNTs/C-SO3H/PPy) was synthesized by the in situ chemical polymerization of pyrrole on the non-covalent sulfonated MWCNTs (MWCNTs/C-SO3H) using ammonium persulfate as oxidant at low-temperature. Fourier transform infrared (FT-IR) spectra confirm the modification of MWCNTs and an existence of interaction between the –SO3H group of the modified MWCNTs and the N–H group of PPy. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), FT-IR and ultraviolet–visible (UV–vis) spectra show that uniform PPy layer coated on the sidewall of MWCNTs/C-SO3H. The electrochemical properties of the MWCNTs/C-SO3H/PPy composite were studied by cyclic voltammetry and galvanostatic charge/discharge test. The composite possesses good rate response and stable specific capacitance, the specific capacitance loss is only 3% even after the 1000 cycles.
Keywords: Electrochemical capacitor; Polypyrrole; Carbon nanotubes
Flexible pentacene organic field-effect phototransistor
by Fahrettin Yakuphanoglu; W. Aslam Farooq (pp. 379-383).
A photoresponsive organic field-effect transistor was fabricated on indium tin oxide deposited onto polyethersulphone flexible substrate with pentacene as the active material and poly(4-vinyl phenol) as the dielectric material. The mobility, threshold voltage and maximum number of interface traps for the pentacene-OTFT under dark, UV and white light illuminations were found to be 2.22×10−1cm2/Vs, 12.97V, 1.472×1013eV−1cm−2 and 2.93×10−1cm2/Vs,14.84V, 1.431×1013eV−1cm−2 and 2.95×10−1cm2/Vs, 17.70V, 1.447×1013eV−1cm−2, respectively. The phototransistor under UV and white illuminations exhibits a high photosensitivity in the off state. The obtained results indicate that the flexible pentacene transistor could be potentially used in photodetectors by a white light and UV optical gate.
Keywords: Organic thin film transistor; Pentacene; Thermal evaporation
In situ electrochemical preparation and characterization of PEDOT–Prussian blue composite materials
by Stelian Lupu (pp. 384-390).
Cyclic voltammograms recorded at PEDOT–PB-soluble composite modified electrodes prepared by potentiodynamic and galvanostatic methods.Display Omitted▶ Electrochemical in situ preparation of Prussian blue on PEDOT. ▶ Electrochemical characterization of soluble and insoluble PB–PEDOT composite materials. ▶ High sensitivities towards hydrogen peroxide detection.Inorganic–organic composite electrode materials consisting of Prussian blue (PB) and poly[3,4-ethylenedioxythiophene] (PEDOT) were developed. The composite inorganic–organic coatings have been prepared by electrochemical methods in various compositions onto Pt electrode substrate. The composite coatings were prepared by both potentiodynamic and galvanostatic methods. The electrochemical properties of these composites materials were investigated by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The electrochemical behavior of the electrode materials is based mainly on the redox reaction of the inorganic component. The thickness of the composite coatings was estimated from EQCM data. The potentiodynamic method proved to be more efficient for the incorporation of soluble PB within the PEDOT matrix, while the galvanostatic method showed an enhanced efficiency in the incorporation of insoluble PB. The preparation of both insoluble and soluble PB forms within the PEDOT coating and the investigation of their electrochemical properties and analytical applications in the amperometric determination of hydrogen peroxide are also presented. The composite coatings prepared through galvanostatic methods showed larger sensitivities for hydrogen peroxide detection in comparison with those prepared by potentiodynamic method.
Keywords: Modified electrode; Composite inorganic–organic coating; Prussian blue; Poly(3,4-ethylenedioxythiophene); Cyclic voltammetry; Electrochemical quartz crystal microbalance
Blue emitting amino-DPQ with PS and PMMA phosphors for organic light emitting diode
by S.B. Raut; S.J. Dhoble; R.G. Atram (pp. 391-396).
▶ The blended thin films of synthesized polymeric compound at lower concentration are cost effective and give better emission in blue region. ▶ These outstanding properties make amino-DPQ, attractive candidates as advanced materials in the field of photonics and electronics. ▶ In term of applications, with inorganic or metallic materials, organic molecules and their derivatives and complexes have drawn many researchers’ interest as candidate materials for nanoscale electronic devices of the next generation.New conjugated polymer, 2(4′-aminophenyl)-4-phenylquinoline i.e., amino-DPQ have been synthesized by Friedlander condensation method at 140°C. The Optical, structural and thermal properties of the amino-DPQ has been studied. The blended thin films of amino-DPQ with PMMA and PS at different wt% concentrations have been prepared. The UV–vis absorption spectra could provide a good deal of information on the electronic structures of the polymeric compound. When powder form of amino-DPQ is excited at 385nm, it emits intense blue light of wavelength 486nm. The blended thin films of amino-DPQ with PMMA and PS at different wt% concentrations show the emission peak in the range of 415–450nm. Hence, the blue emitting 2(4′-aminophenyl)-4-phenylquinoline (amino-DPQ) has generated considerable interest owing to their good photoluminescence efficiencies.
Keywords: Polymer; Photoluminescence; Phosphor; Lighting; Synthesis
Carboxymethylcellulose: A conductivity enhancer and film-forming agent for processable polypyrrole from aqueous medium
by Claudia Sasso; Davide Beneventi; Elisa Zeno; Michel Petit-Conil; Didier Chaussy; Mohamed Naceur Belgacem (pp. 397-403).
▶ Carboxymethylcellulose (CMC) enhanced the conductivity of chemically synthesised PPy. ▶ The higher the CMC molecular weight the lower the PPy conductivity. ▶ Presence of a two regimes polymerisation process in PPy–CMC–APS systems at both 3 and 24°C. ▶ An inverse relationship between polymerisation yield and electrical properties was found. ▶ Elaboration of CMC–PPy conducting films using CMC as conductivity enhancer and film forming agent.The use of carboxymethylcellulose (CMC) in polypyrrole (PPy) synthesis and in the production of PPy freestanding films was investigated. PPy was synthesised by chemical oxidative polymerisation in aqueous solutions using ammonium persulfate (APS) as oxidant and CMC as conductivity enhancer (CMCd). CMCs with different molar weight, namely 90,000 and 250,000g/mol, were tested. The influence of polymerisation temperature, time, and CMC concentration, on the conductivity of PPy was evaluated thus showing that higher conductivities were obtained at low temperature, short polymerisation time and in the presence of low molar weight CMC. A long time polymerisation study was carried out at 3°C and 24°C revealing the presence of a double regime polymerisation process, with second regime rates depending on the polymerisation temperature.CMC was also used to improve the limited film forming ability of PPy by dispersing preformed PPy particles in CMC aqueous solutions. When decreasing the weight fraction of film forming CMC, semiconducting, flexible and freestanding films with thickness of 50–100μm were obtained and their conductivity increased proportionally to the CMC weight fraction.
Keywords: Carboxymethylcellulose; Polypyrrole; Conducting films
Rapid microwave-assisted synthesis of graphene nanosheets–zinc sulfide nanocomposites: Optical and photocatalytic properties
by Huating Hu; Xianbao Wang; Fangming Liu; Jingchao Wang; Chunhui Xu (pp. 404-410).
Graphene nanosheets coated with face-centered cubic zinc sulfide (ZnS) nanoballs were prepared in aqueous medium assisted by microwave irradiation. The as-prepared nanocomposites show an excellent photocatalytic activity toward the photodegradation of methylene blue.Display Omitted▶ Graphene nanosheets coated with ZnS nanoballs (GNS–ZnS) by microwave irradiation. ▶ GNS–ZnS display two ultraviolet emission peaks and a blue emission band. ▶ GNS–ZnS show an excellent photocatalytic degradation activity to methylene blue.A facile and efficient strategy for preparing graphene nanosheets–zinc sulfide (GNS–ZnS) nanocomposites assisted by microwave irradiation for the first time is demonstrated. This process involved the reaction of graphene oxide nanosheets as a dispersant and two-dimensional growth template for ZnS nanoballs, zinc acetate as a zinc source, and thioacetamide (TAA) as a sulfide source as well as a reducing agent, resulting in the in situ formation of ZnS nanoballs with an average diameter of 41.9nm supported on graphene oxide nanosheets and simultaneous reduction of graphene oxide nanosheets to graphene nanosheets. It has been found that the ZnS nanoballs are composed of many small self-assembled ZnS crystals (subunits) with an average size of 3nm. Photoluminescence measurements show that there is photoinduced electron transfer between ZnS and GNS. Furthermore, the as-prepared graphene-based nanocomposites show an excellent photocatalytic activity toward the photodegradation of methylene blue. The detailed formation and photocatalytic mechanism are also provided here.
Keywords: Graphene; Zinc sulfide; Nanocomposites; Microwave; Photocatalytic activity
Morphology and thermal properties of PAN copolymer based electrospun nanofibers
by Sanjay R. Dhakate; Ashish Gupta; Anurag Chaudhari; Jai Tawale; Rakesh B. Mathur (pp. 411-419).
Ultra-thin fibers are obtained from polyacrilonitrile co-polymer (PAN-CP)/N,N-dimethylformamide (DMF) solution by electro-spinning technique. The different wt. content of PAN-CP solution is electrospun with varying processing parameters to get nanofibers. The morphology of nanofibers is studied by scanning electron microscopy (SEM) and thermal properties are primarily investigated by DSC and TGA. The polymer nanofibers are stabilized and carbonized to get carbon nanofibers, after stabilization and carbonization nanofibers are characterized by FTIR, XRD, SEM and SPM. It is found that the diameter of nanofibers varies from 150 to 1300nm, that increases with increasing polymer concentration and decreases with increasing the tip to collector distance and collector speed. The DSC studies show that the exothermic peak occurs at two different temperatures 275 and 320°C in case of nanofibers. While in case of micron fiber single exothermic peak occurs at ∼275°C. This might be due to the alignment of polymeric chain along the fiber direction. This is due to the stretching and whipping that occurs during the electrospinning process. As a consequence, increase in thermal stability and decrease in weight of nanofibers is confirmed by TGA. However, in the nanofibers of diameter >1000nm, weight loss pattern is found to be similar as that of micron fibers. This could be due to the entrapping of solvent between polymeric chains. On stabilization and carbonization there is a decrease in fiber diameter in all the cases. The extent of decrease is higher in case of 10wt.% electrospun fibers, from 350–400nm to 100nm. The SPM investigations reveal that the surface area and roughness changes due to the transverse shrinkage of nanofibers.
Keywords: Electrospinning; Nanofibers; Thermal stability; Microstructure; SEM; SPM
Microwave absorption properties of PANI/CIP/Fe3O4 composites
by Zhifu He; Yang Fang; Xiaojuan Wang; Hua Pang (pp. 420-425).
The PANI/carbonyl iron powders (CIP)/Fe3O4 composite was synthesized by mechanical mixing PANI/CIP composite with PANI/Fe3O4 composite with mass ratio of 7:3. The electromagnetic (EM) properties of these composites were studied at 0.5–18GHz. Compared with PANI/CIP and PANI/Fe3O4 composites, the PANI/CIP/Fe3O4 composites show enhanced EM wave absorption at high frequency range, and the maximum reflection loss is −48.3dB at 9.6GHz with a thickness of 1.76mm. There is no obvious chemical interaction happened during mixing, which retains the magnetic properties of PANI/CIP and PANI/Fe3O4 components. While the conducting channels of the PANI coatings and the metal–polymer interfaces are partly destroyed, which reduces the permittivity and improves the impedance match, hence results in good EM wave absorption for PANI/CIP/Fe3O4 composite.
Keywords: Polyaniline composites; Electro-magnetic function; Microwave absorption; Impedance match
Solution-processed small molecular electron transport layer for multilayer polymer light-emitting diodes
by Zong-You Liu; Shin-Rong Tseng; Yu-Chiang Chao; Chun-Yu Chen; Hsin-Fei Meng; Sheng-Fu Horng; Yu-Hsun Wu; Su-Hua Chen (pp. 426-430).
▶ We achieved an all solution-processed multilayer PLED by blade coating method. ▶ Three common small molecular electron transport materials were blade coated from methanol without dissolution problem between layers. ▶ High efficiency PLED can be achieved by multilayer structure.Solution-processed electron transport layers (ETL) have been fabricated by solution process and applied in multilayer polymer light-emitting diodes with tris[2-(p-tolyl)pyridine]iridium(III) blended in poly(vinylcarbazole) as the emissive layer. Three kinds of small molecular electron transport materials,including 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), 3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ), and 4,7-diphenyl-1,10-phenanthroline (BPhen), are tested and dissolved in methanol to form electron transport layers by blade coating. Such electron transport layer provides efficient electron injection and electron transport ability in the devices. The efficiency of the devices with the combination of ETL and LiF/Al cathode reaches 21.5cd/A at 10V (4050cd/m2). The efficiency of the devices without ETL are 3.5cd/A (13V) for LiF/Al cathode and 17cd/A (7V) for CsF/Al cathode at 1000cd/m2. The aggregation of the solution-processed ETL can be controlled by annealing temperature to further optimize the device performance to maximal efficiency of 53cd/A.
Keywords: Blade coating; Solution-processed electron transport layers
Picosecond laser patterning of PEDOT:PSS thin films
by N.G. Semaltianos; C. Koidis; C. Pitsalidis; P. Karagiannidis; S. Logothetidis; W. Perrie; D. Liu; S.P. Edwardson; E. Fearon; R.J. Potter; G. Dearden; K.G. Watkins (pp. 431-439).
Picosecond pulsed laser (10.4ps, 1064nm, 5 and 50kHz) patterning studies were performed, of PEDOT:PSS thin films of varying thickness deposited by spin coating on glass substrates, by ablating the films or by changing locally by laser irradiation the optical and electrical properties of the polymer. From a detailed observation of the morphology of single pulse ablated holes on the surfaces of the films, in combination with simple calculations, it is concluded that photomechanical ablation is the likely ablation mechanism of the films. The single pulse ablation thresholds were measured equal to 0.13–0.18J/cm2 for films with thicknesses in the region of ∼100–600nm. The implications on ablation line patterning of the films using different fluences, scanning speeds and pulse repetition rates, were investigated systematically. Laser irradiation of the films before ablation induces a metal–insulator transition of the polymer because of the formation of charge localization due to a possible creation of molecular disorder in the polymer and shortening of its conjugation length.
Keywords: PEDOT:PSS; Laser patterning; Raman spectroscopy; Spectroscopic Ellipsometry
A novel amperometric galactose biosensor based on galactose oxidase-poly(N-glycidylpyrrole-co-pyrrole)
by Mehmet Şenel; İbrahim Bozgeyik; Emre Çevik; M. Fatih Abasıyanık (pp. 440-444).
▶ Poly(N-glycidylpyrrole-co-pyrrole) film enable direct covalent immobilization without any reagent. ▶ The biosensor seems to be simple to prepare, fast to respond, inexpensive and sensitive. ▶ The conducting polymer film used in this study is an effective platform to produce reliable biosensors.A novel amperometric galactose biosensor was constructed by immobilization of galactose oxidase (GAox) onto poly(N-glycidylpyrrole-co-pyrrole) film. GAox enzyme was immobilized onto the electrochemically prepared novel conducting polymer film by direct one-step covalent attachment without using any coupling agents. The biosensor surface was characterized by FT-IR spectroscopy and atomic force microscopy (AFM). Amperometric response was measured as a function of concentration of galactose, at fixed potential of +0.7V vs. Ag/AgCl in a phosphate buffered saline (pH 7.5). The mediated hydrogen peroxide biosensor had a fast response of less than 5s with linear range 2–16mM. The sensitivity of the biosensor for galactose was 1.75μA/mM. The factors influencing on the performance of the resulting biosensor were studied in detail.
Keywords: Biosensor; Galactose oxidase; Pyrrole; Immobilization
Synthesis and properties of an ionic polyacetylene by the activated polymerization of 2-ethynylpyridine with the ring-opening of propiolactone
by Yeong-Soon Gal; Sung-Ho Jin; Young-Il Park; Jong-Wook Park; Won Seok Lyoo; Kwon-Taek Lim (pp. 445-449).
Display Omitted▶ A new ionic polyacetylene was synthesized by the activated polymerization of 2-ethynylpyridine with the ring-opening of β-propiolactone without any additional initiator or catalyst. This zwitterionic polymer was soluble in such polar protic solvents as water, methanol, DMF, DMSO, N,N-dimethylacetamide, or organic acids. The cyclovoltammograms of polymer exhibited the irreversible electrochemical behaviors between the oxidation and reduction peaks. The kinetics of the redox process of polymer was found to be almost controlled by the reactant diffusion process from the oxidation current density of polymer versus the scan rates.A new ionic polyacetylene was prepared by the activated polymerization of 2-ethynylpyridine with the ring-opening of β-propiolactone without any additional initiator or catalyst. The polymerization proceed well in homogeneous manner even at the mild reaction conditions to give a high yield of polymer (86%). The chemical structure of polymer was characterized by various instrumental methods to have polyacetylene polymer backbone with (N-propionate)pyridium substituents. This zwitterionic polymer was soluble in such polar protic solvents as water, methanol, DMF, DMSO, N,N-dimethylacetamide, or organic acids capable of hydrogen bonding with the propionate anion. The electrical conductivity of iodine-doped ionic polyacetylene was 3.4×10−3S/cm. The photoluminescence spectrum of polymer showed that the PL peak is located at 490nm corresponding to the photon energy of 2.53eV. The cyclovoltammograms of polymer exhibited the irreversible electrochemical behaviors between the oxidation and reduction peaks. The oxidation current density of polymer versus the scan rates is approximately linear relationship in the range of 30–120mV/s. It was found that the kinetics of the redox process of polymer is almost controlled by the reactant diffusion process from the oxidation current density of polymer versus the scan rates.
Keywords: Polyacetylene; 2-Ethynylpyridine; Propiolactone; Electrical conductivity; Photoluminescence; Cyclic voltammogram
Violet electroluminescence from poly( N-vinylcarbazole)/ZnO-nanrod composite polymer light-emitting devices
by Ming-Lung Tu; Yan-Kuin Su; Shang-Shang Wu; Tzung-Fang Guo; Ten-Chin Wen; Chun-Yuan Huang (pp. 450-454).
▶ Poly( N-vinylcarbazole) and ZnO-nanorods are used as composite polymer. ▶ Violet electroluminescence is enhanced from composite polymer light-emitting device. ▶ Violet electroluminescence is improved by nanometer film of polyethylene oxide.In this paper, we have demonstrated the violet electroluminescence (EL) of poly( N-vinylcarbazole) (PVK) and ZnO-nanorods composite polymer light-emitting device (PLED). The structure of PLED is PVK/ZnO-nanorods composite layer sandwitched between an anode and a cathode. The composite layer is made by mixing PVK and semiconducting ZnO nanorods with proper weight (wt.) ratio. Furthermore, the nanometer scale polyethylene oxide (PEO) is inserting as a modified cathode. The PEO film is deposited by thermal evaporation. Composite PLED appears violet emission with a main 440nm EL peak, attributed to singlet excimer. A 607nm EL peak is exhibited from triple excimer of the composite PLED. Both the main EL peak intensity and the triple EL peak intensity of composite PLED are enlarged by incorporating ZnO nano-materials into PVK.
Keywords: Polymer light-emitting device (PLED); ZnO nanorod; Nonconjugated organic polymer; Thermal evaporation
A novel main chain polymeric metal complex based on Zn(II) with thiophene and 2-(2′-pyridyl)benzimidazole ligand: Synthesis, characterization, photovoltaic property and application in DSSCs
by Qian Xiu; Hui Huang; Yuan Liu; Lirong Zhang; Lihui Guo; Jinyan Deng; Gaojun Wen; Songting Tan; Chaofan Zhong (pp. 455-459).
Dye-sensitized solar cells (DSSCs) have extensive interests in recent years because of their unique advantages: low cost, simple preparation technologies and high efficiency. A novel main chain polymeric metal complex of [2-(2′-pyridyl)benzimidazolyl]-3-methylthiophene (Bmtp) with Zn (II) was designed and investigated as dye sensitizers for dye-sensitized solar cells (DSSCs). This polymer was found to be good stabilities with thermal decomposition temperatures at 292°C and high glass transition temperature (152°C), which indicates this polymer could be applied as photovoltaic material for DSSCs. The obtained polymer exhibited good photovoltaic property. The DSSCs based on Bmtp-Zn exhibited a maximum power conversion efficiency (PCE) up to 1.88% ( Jsc=4.09mA/cm2, Voc=0.65mV, and FF=0.71) under simulated AM 1.5G solar irradiation (90–95mW/cm2).
Keywords: Dye-sensitized solar cells; Thiophene; 2-(2′-Pyridyl)benzimidazole; Polymeric metal complex
Electroluminescence overshoot effect in single layer pulsed organic light emitting diodes
by V.K. Chandra; M. Tiwari; B.P. Chandra; M. Ramrakhiani (pp. 460-465).
▶ A theoretical approach is made to the overshoot effect in single layer OLEDs. ▶ Rise and fast decay in EL overshoot is caused by the recombination luminescence. ▶ Slow decay in EL overshoot is caused by the geminate recombination. ▶ Using the dynamics of EL overshoot, several parameters of OLEDs can be determined.After switching off the applied voltage pulse to a single layer organic light emitting diode (OLED) such as ITO/MEH-PPV/Al, initially the electroluminescence (EL) decays rapidly corresponding to the discharging of the parallel plate capacitor of the device, however, after a delay of 1–2μs, the EL intensity rises again, attains a peak value, and then decays slowly without the application of an electric field. The EL intensity and the position of the peak in this overshoot depend on temperature. The intensity of EL overshoot increases with increasing pulse duration but the position of spike is independent of the pulse duration. A phenomenological theory is explored for the EL overshoot produced during the turn off of single layer OLEDs. The EL transient after the turn off of the external bias can be divided into the following three regions: (i) fast decay region, (ii) delayed peak region, and (iii) slow decay region. The initial fast decay is attributed to the recombination of injected charge carriers; the rise and exponential decay just after the peak in the delayed EL peak are due to the recombination luminescence owing to the movement of detrapped holes with noncorrelated electrons; and the slowly decaying EL following power law t− z ( z lying between 1.5 and 2) is due to geminate recombination of the correlated electron–hole pairs. The release time τ r of holes trapped at Al2O3/polymer interface, the activation energy E a for the detrapping of holes from the interface and the time–constant of the OLED circuit, can be determined from the measurement of the time dependence of EL overshoot. A good agreement is found between the theoretical and experimental results.
Keywords: Organic light emitting diodes; Electroluminescence; Overshoot effect; Displays; Optoelectronics
Tuning of HOMO levels of carbazole derivatives: New molecules for blue OLED
by Neeraj Agarwal; Pabitra K. Nayak; Farman Ali; Meghan P. Patankar; K.L. Narasimhan; N. Periasamy (pp. 466-473).
The Suzuki–Miyaura coupling between 3,6-dibromo-N-hexylcarbazole and aryl-boronic acids catalyzed by Pd(PPh3)4 afforded blue emitting molecules, 3,6-diaryl-N-hexylcarbazole: aryl=phenyl (1), p-methoxyphenyl (2), p-cyanophenyl (3), p-acetophenyl (4), pyrenyl (5), biphenyl (6), difluorophenyl (7) and p-nitrophenyl (8), in good yield. The HOMO level of the carbazole derivative varied between −5.67 and −6.02eV due to the electron-withdrawing or donating substituent in the aryl group. This is confirmed by the linear correlation of the Hammett parameter of the substituent in the phenyl group with oxidation potential or energy levels. Density functional theory calculation (B3LYP/6-31G*) of carbazole derivatives confirmed the experimentally observed trend. Blue fluorescence quantum yield of these molecules is high (0.19–0.96), except for the nitrophenyl derivative (<0.1). Single layer organic light emitting devices (OLEDs) using spin-coated films of2–5 showed blue electroluminescence (EL) with a turn-on voltage at ∼6–7V. The performance of blue EL of molecules3 and4 improved dramatically (turn-on at ∼3V, brightness at ∼1000cd/m2, efficiency at ∼1cd/A) in a multilayer OLED designed using standard molecules as electron and hole transport layers for efficient and balanced carrier injection.
Keywords: Carbazole; Suzuki–Miyaura coupling; Electroluminescence; OLED; Blue EL
The Au/polyvinyl alcohol (Co, Zn-doped)/n-type silicon Schottky barrier devices
by İlbilge Dökme; T. Tunç; İ. Uslu; Ş. Altındal (pp. 474-480).
Metal/polyvinyl alcohol/n-type silicon Schottky barrier (SB) devices have been fabricated in this study. The importance of this study is that PVA (Co, Zn doped) nanofiber film as an interfacial layer was formed by the electrospinning technique on n-type silicon substrate. The forward and reverse bias current–voltage ( I– V) characteristics of this device were measured at room temperature. The Φ Bo value of about 0.749eV obtained from I– V characteristics indicates that the contact potential barrier exists at the interface between organic and inorganic semiconductor layer, that is, PVA/n-Si interface. The variation in the capacitance–voltage ( C– V) and conductance–voltage ( G/ ω– V) characteristics of the Au/PVA (Co, Zn doped)/n-Si SB devices have been systematically investigated as a function of frequencies in the frequency range of 2kHz–2MHz at room temperature. The effects of density of interface states ( N ss) and series resistance ( R s) on I– V, C– V and G/ ω– V characteristics were investigated. The high-frequency capacitance ( C m) and conductance ( G m/ ω) values measured under reverse bias were corrected to decrease the effects of series resistance. These results show that the locations of interface states between Si/PVA and series resistance have a significant effect on electrical characteristics of the Au/PVA (Co, Zn doped)/n-Si SB devices.
Keywords: Au/PVA (Co, Zn-doped)/n-Si; Electrical properties; FT-IR; Electrospinning technique
Electronic properties of soluble functionalized polyaniline (polyanthranilic acid)-multiwalled carbon nanotube nanocomposites: Influence of synthesis methods
by Arun Kumar Singh; Leela Joshi; Bhavana Gupta; Ashish Kumar; Rajiv Prakash (pp. 481-488).
Processible nanocomposites of carboxyl functionalized conducting polymer “polyanthranilic acid” (PANA) with multiwalled carbon nanotubes (MWNTs) are prepared using two different synthesis routes viz. single phase and two phase polymerization. The novel nanocomposite materials are characterized using X-ray diffraction (XRD), thermogravimetric (TGA), electrochemical impedance (EI), scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM) techniques for their structural, thermal, electrochemical and surface morphological properties. SEM and HRTEM images are confirmed that nanotubes are dispersed uniformly in polymer matrix and polymer chains wrap around the nanotubes walls. The interaction between MWNTs and PANA is analyzed by Raman and Fourier transform infrared (FTIR) spectroscopy. UV–vis spectroscopic technique is used to obtain the optical bandgap of nanocomposites. PANA-MWNTs nanocomposites are used for the first time for fabrication of sandwich type devices with a configuration of metal Al/PANA-MWNTs nanocomposite/indium tin oxide coated glass (ITO). The current density–voltage ( J– V) and capacitance–voltage ( C– V) characteristics of the Schottky diode are subsequently used for extracting electronic parameters of the devices. These measurements revealed that the junction electrical parameters depend strongly on the synthesis route for preparation of nanocomposites.
Keywords: Polyanthranilic acid; Multi walled carbon nanotube; Nanocomposite; Conducting polymer; Schottky diode; Metal-polymer junction property
Tuning the electronic properties of monolayer graphene by the periodic aligned graphene nanoribbons
by C.H. Lee; S.C. Chen; W.S. Su; R.B. Chen; M.F. Lin (pp. 489-495).
The 2 p z tight-binding model has been used to investigate the electronic properties of ribbon–graphene hybrid systems. This system is constructed by zigzag graphene nanoribbons aligned periodically on monolayer graphene. It was found that for such systems the electronic properties would be strongly influenced by the geometric structure of graphene nanoribbons, such as the width and the period of the ribbons. In addition, the stacking arrangement between graphene nanoribbons and monolayer graphene also plays a dominant role in determining the band structures in the low-energy region. These geometric structure effects can be well understood through the density of state calculations. Such hybrid structures lead to interesting novel features, dissimilar from those of single layer graphene, and could serve as a platform for the studies of device applications.
Keywords: PACS; 71.20.Tx, 73.20.−r, 73.21.−bGraphene nanoribbons; Monolayer graphene; Electronic properties
Synthesis of triarylamine dyes containing secondary electron-donating groups and application in the dye-sensitized solar cells
by Ying-Jun Xu; Mao Liang; Xiu-Jie Liu; Hong-Yu Han; Zhe Sun; Song Xue (pp. 496-503).
Three triarylamine organic dyes (XS19–21) containing N,N-dimethylaniline and butoxybenzene units as secondary electron-donating groups are synthesized and characterized. When these dyes were applied into nanocrystalline TiO2 dye-sensitized solar cells through standard operations, high open-circuit voltage (more than 730mV) were obtained. The effects of the secondary electron-donating groups as well as the π spacers on the photovoltaic performance of the DSSCs were examined. For a typical device, 5.79% of solar energy conversion efficiency ( η) based on XS21 was achieved with a short-circuit photocurrent density ( JSC) of 10.0mAcm−2, an open-circuit voltage ( VOC) of 782mV, and a fill factor ( ff) of 0.74.
Keywords: Dye-sensitized solar cell; Photovoltaic; Triarylamine; Electron-donating groups
Preparation of photonic crystal heterostructures composed of two TiO2 inverse opal films with different filling factors
by Aijun Wang; Sheng-Li Chen; Peng Dong; Zheng Zhou (pp. 504-507).
A novel fabrication procedure for preparing TiO2 inverse opal heterostructures is presented in this paper. In this procedure, TiO2 inverse opal film was fabricated by filling a polystyrene (PS) opal photonic crystals template through a liquid-phase deposition (LPD) technique. The PS opal photonic crystals templates were fabricated using a room temperature floating self-assembly (RTFSA) method, which was recently developed in our lab. And a photonic crystal heterostructure composed of two TiO2 inverse opal films with different filling factors was fabricated through the sequential deposition, infiltration and removal of two PS opal template films. Herein, the two opal template films are assembled with PS microspheres of the same size. The inverse opal heterostructures with different photonic band structures can be easily fabricated by varying the deposition time of the LPD step.
Keywords: PACS; 42.70.Qs; 81.16.Dn; 74.78.FkColloidal photonic crystal; Inverse opal heterostructures; Floating self-assembly; Liquid-phase deposition
Novel water-soluble metal-free and metallophthalocyanines: Synthesis, spectroscopic characterization and aggregation properties
by Zekeriya Bıyıklıoğlu (pp. 508-515).
In this study, the preparation of novel metal-free phthalocyanine2, metallophthalocyanine complexes3,4,5,6 (MPcs, M=Ni, Co, Cu, Fe) with 6-oxyquinoline functional group and quaternized metallophthalocyanine derivatives3a,4a,6a (MPcs, M=Ni, Co, Fe), was achieved. The reaction of 4-(quinolin-6-yloxy)phthalonitrile1 in 2-(dimethylamino)ethanol as the solvent, the metal-free phthalocyanine2 was synthesized. The synthesis of metallophthalocyanines3–6 derived from 4-(quinolin-6-yloxy)phthalonitrile1 were carried out by microwave irradiation. Aggregation properties of Pcs were investigated at different concentrations in chloroform, dimethylsulfoxide, dimethylformamide and water. The metal-free phthalocyanine2 showed the aggregation in polar solvent DMSO, whereas in chloroform no aggregation was observed. The effect of the concentration on the aggregation properties of complexes2,3,4 and5 were studied in chloroform. No aggregation was demonstrated in chloroform from concentration between 1×10−5 and 0.4×10−5M. The new compounds have been characterized by using elemental analysis, UV–Vis, IR,1H NMR,13C NMR and MS spectroscopic data.
Keywords: 6-Oxyquinoline; Metallophthalocyanine; Synthesis; Microwave; Aggregation; Quaternization
Electrically conductive adhesive based on acrylate resin filled with silver plating graphite nanosheet
by Yi Zhang; Shuhua Qi; Xinming Wu; Guochen Duan (pp. 516-522).
Silver plating graphite nanosheet (Ag plating NanoG) is an effective approach to obtain the conductive filler with high electrical conductivity and moderate cost. Ag plating NanoG was prepared by electroless plating method using graphite nanosheet (NanoG) from expanded graphite (EG). Then a novel electrically conductive adhesive (ECA), comprising acrylate resin and Ag plating NanoG as conductive filler, was studied. The microstructures of Ag plating NanoG and ECA were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transmission infrared (FT-IR), transmission electron microscope (TEM). The results showed that the Ag plating NanoG was successfully developed and it was homogeneously dispersed in the acrylate resin. The electrical conductivity of the ECA increased to 2.60×10−2S/cm and the 180° peel strength and shear strength remained at a high level when the content of the conductive filler was 40wt%. From the thermogravimetric analysis, the ECA exhibited good thermal stability.
Keywords: Ag plating NanoG; Acrylate resin; Electrically conductive adhesive; Electrical conductivity; Thermal property
Electrical and thermal properties of PEDOT:PSS films doped with carbon nanotubes
by Jongwoon Park; Ari Lee; Younchan Yim; Eunmi Han (pp. 523-527).
We report on a highly conductive polymer composite where poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is doped with dimethylsulfoxide (DMSO) and carbon nanotubes (CNTs). By the addition of single-walled CNTs (SWCNTs) into the DMSO-doped PEDOT:PSS solutions, the sheet resistance can be lowered from 279Ω/□ to 150Ω/□ without any compromise on the optical transmittance (81% at 520nm) and surface morphology (∼2nm). Through the measurement using Fourier transform infrared (FT-IR) spectrometer, it is found that the conductivity enhancement by the addition of CNTs is related to the bonding disruption of SO3H group with the insulating PSS chains. Furthermore, the enhanced thermal conductivity of the nanocomposite is demonstrated by its heat dissipation capability.
Keywords: Conductive polymer; PEDOT:PSS; CNT; DMSO; Sheet resistance; FT-IR
Coulomb gap variable range hopping in graphitized polymer surfaces
by Y. Koval; I. Lazareva; P. Müller (pp. 528-534).
The conductivity of several polymers was investigated after low-energy ion irradiation. The enhancement of conductance induced by the ions is discussed in terms of graphitization. We have found that the transport in the graphitized surfaces can be consistently described in terms of the 2D Coulomb gap variable range hopping theory. However, analyzing the properties of the pre-exponential factor in the temperature dependence of conductance and current–voltage characteristics we found several contradictions with existing theories.
Keywords: Ion irradiation; Polymers; Graphitization; Variable range hopping; Pre-exponential factor
Synthesis, characterization and third-order nonlinear optical studies of copper complexes containing 1,10-phenanthroline-5,6-dione and triphenylphosphine ligands
by B.J. Rudresha; B. Ramachandra Bhat; H.C. Sampath Kumar; K.I. Shiva Kumar; K. Safakath; Reji Philip (pp. 535-539).
▶ In this study we have synthesised and characterized the copper complexes containing 1,10-phenanthroline-5,6-dione and triphenylphosphine ligands. ▶ Nonlinear optical measurements of the complexes were carried out at 532nm with nanosecond laser pulses using Z-scan technique and degenerate four wave mixing technique (DFWM). ▶ The values of the effective two-photon absorption (2PA) coefficients ( β), third-order nonlinear susceptibilities ( χ(3)) and figures of merit ( F), are calculated. ▶ The complexes show optical limiting behaviour due to “effective” two-photon absorption. ▶ The high thermal stability and large optical nonlinearity of these complexes make them potential candidates for photonic applications.This research article describes the synthesis, characterization and third-order nonlinear optical studies of copper(I) complexes [Cu(Br)(N,N′-C12H6N2O2)(PPh3)] and [Cu(I)(N,N′-C12H6N2O2)(PPh3)] abbreviated as [CuBrLPPh3] (1) and [CuILPPh3] (2) (L=1,10-phenanthroline-5,6-dione). Nonlinear optical properties of the complexes are investigated at 532nm using single beam Z-scan and degenerate four-wave mixing (DFWM) techniques employing nanosecond laser pulses. The complexes show optical limiting behaviour due to “effective” two-photon absorption. The values of the effective two-photon absorption (2PA) coefficients ( β), third-order nonlinear susceptibilities ( χ(3)), and figures of merit ( F), are calculated.
Keywords: Copper complexes; 1,10-Phenanthroline-5,6-dione; LMCT; Two-photon absorption; Z-scan; Degenerate four wave mixing
Nonlinear electrical conduction in percolating systems induced by internal field emission
by Linxiang He; Sie-Chin Tjong (pp. 540-543).
► Percolating high density polyethylene (HDPE)-carbon nanofiber (CNF) composite. ► The electrical behavior under an applied field ( E) is described by linear and nonlinear conduction. ► Nonlinear conduction in percolating HDPE-CNF composite results from internal field emission. ► The current density ( j) is j( E)= σ0 E+ AE nexp(− B/ E) where A, B are constants and n an exponent. ► A model is proposed for percolating composite system, consisting of two resistors in parallel.We identify the mechanism of internal field emission responsible for nonlinear electrical conduction behavior of percolating systems. The nonlinear conduction induced by internal field emission, in combination with linear conduction contributed by a conducting network, are responsible for the whole electrical conduction process in the percolating system. Based on these two types of conduction, we put forward an elegant electrical model, demonstrating the system exposed to an external field behaves as two resistors in parallel. Moreover, we also analyze the crossover current density where significant electrical nonlinearity occurs. Although our conclusion is based on high density polyethylene (HDPE)–carbon nanofiber (CNF) system, it can be extended to other systems such as HDPE–graphite, polyvinylidene fluoride (PVDF)–CNF, and PVDF–graphite.
Keywords: Internal field emission; Conductivity; Nanocomposite; Carbon nanofiber
Dangerous, an explosion of polyaniline nanomaterials
by Hairui Zhang; Jixiao Wang; Changlin Zhang; Zhi Wang; Shichang Wang (pp. 544-547).
Polyaniline nanomaterials were successfully prepared by potentiostatic polymerization method, and then post-treated by the aqueous solution containing HClO4 and H2O2, I2, FeCl3, or APS, respectively. The product was dried under vacuum condition at least 72-h, and then it was characterized by SEM, FTIR and UV–Vis techniques. While product treated with H2O2 was weighed, an accident, an explosion of polyaniline nanowires broke out. Here, experimental process is reported in detail and the explosive mechanism is proposed, and thus providing a warning for PANI nanomaterials research and production.
Keywords: Polyaniline; Explosion; Nanomaterial; Perchloric acid; Hydrogen peroxide
Synthesis and electrochemical properties of gyroscope-like lithium iron phosphate/multiwalled carbon nanotubes composites by microwave-assisted sol–gel method
by Yong Zhang; Peipei Du; Lizhen Wang; Aiqin Zhang; Yanhua Song; Xiaofeng Li; Yan Lv (pp. 548-551).
Gyroscope-like microparticle of lithium iron phosphate/multiwalled carbon nanotubes composites is synthesized by microwave-assisted sol–gel method with ferrous oxalate, lithium carbonate, and ammonium dihydric phosphate as raw materials. This new composites with gyroscope-like have not been reported in the literature. The crystal structure and surface morphology of the as-prepared particles are characterized by X-ray diffraction and transmission electron microscopy tests, and their electrochemical properties are investigated by cyclic voltammetry and galvanostatic charge/discharge tests. The results demonstrated that the composites have an olivine structure and superior electrochemical performances in terms of discharge capacity, cycling stability and rate capability. These favorable electrochemical properties should be attributed to its special gyroscope-like microstructure.
Keywords: Gyroscope-like microstructure; Lithium iron phosphate/multiwalled carbon nanotubes composites; Electrochemical properties; Microwave-assisted sol–gel method