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1.	Ruseckas, A., et al. (författare) Luminescence from inter-chain aggregates in polythiophene films 2001 Ingår i: Synthetic Metals. - 0379-6779 .- 1879-3290. ; 119:1-3, s. 603-604 Tidskriftsartikel (refereegranskat)abstract We report time-resolved photoluminescence of two polythiophene derivatives with different chain packing. Emission of inter-chain aggregates is distinguished from that of intra-chain singlet excitons. The aggregate luminescence is shifted towards lower energies relative to that of intra-chain exciton by 0.17 eV, and the Huang-Rhys factor of the coupling to the intra-chain C double bondC vibration is S = 1.5. The excitonic coupling in aggregates is of intermediate strength.
2.	Theander, M., et al. (författare) Interchain photoluminescence in substituted polyfluorenes 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 119:1-3, s. 615-616 Tidskriftsartikel (refereegranskat)abstract We have characterised the interchain emitting states of two substituted polyfluorenes with steady-state and time-resolved photoluminescence (PL). Site selective excitation of the interchain state shows that physical dimers are formed in the film. These dimers have low concentration in the films but exciton diffusion to the dimers is reducing the intrachain exciton lifetime. With asymmetrical substituents, the PL quantum yield is higher and the PL lifetime is longer due to lower concentration of dimers. Slow cooling from the melt, gives a new red shifted emission band and less intrachain emission. A discrepancy in the calculated radiative lifetimes suggest a fast formation of this new band.
3.	Jager, Edwin, 1973-, et al. (författare) Polypyrrole micro actuators 1999 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 102:1-3, s. 1309-1310 Tidskriftsartikel (refereegranskat)abstract The doping and undoping of conjugated polymers is accompanied by a volume change. This volume change can be used to make micro-actuators. We have built polypyrrole (PPy) gold bilayer structures. The volume change of PPy induces a bending of the bilayer. We have made micro-actuators based on this principle, which have been examined with video-microscopy. Some applications for these microactuators are proposed, including opening and closing boxes for cell biology and nanoliter chemistry and micro-robotics.
4.	Aasmundtveit, K.E., et al. (författare) Structural aspects of electrochemical doping and dedoping of poly(3,4-ethylenedioxythiophene) 2000 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 113:1, s. 93-97 Tidskriftsartikel (refereegranskat)abstract Electrochemical dedoping and redoping of p-toluene sulfonate doped poly(3,4-ethylenedioxythiophene) (PEDOT) has been studied with in situ grazing incidence diffraction with water used as an electrolyte. The diffraction peak positions and integrated intensities do not change significantly during doping and dedoping, while the peak widths increase upon dedoping and decrease upon doping. This implies that the lattice parameters and the relative positions of the polymer chains and the p-toluene sulfonate ions remain unchanged, the redox processes being carried out by the motion of smaller ions between the polymer and the electrolyte, and that the structural order decreases upon dedoping and increases upon doping in a reversible manner.
5.	Andersson, Mats R., et al. (författare) Improved photoluminescence efficiency of films from conjugated polymers 1997 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 85:1-3, s. 1383-1384 Tidskriftsartikel (refereegranskat)abstract We have demonstrated two general ways to increase the photoluminescence efficiency of films from conjugated polymers. One is to disperse the conjugated polymer on a molecular level by using attractive forces between the conjugated polymer and the matrix. The other method is to substitute the conjugated polymer with side chains which separates the conjugated backbones. Using this idea a new poly(thiophene) with a photoluminescence efficiency of 16% in films has been prepared. LEDs from this polymer exhibit an external efficiency of 0.1% for single layer and 0.7% for double layer diodes.
6.	Andersson, Mats R., et al. (författare) Synthesis of poly(alkylthiophenes) for light-emitting diodes 1995 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 71:1-3, s. 2183-2184 Tidskriftsartikel (refereegranskat)abstract We have demonstrated a general way to tune the emission of poly(alkylthiophenes) by using steric interaction between the repeating units. Light-emitting diodes prepared of the polymers have blue to near-infrared emission.
7.	Andersson, M.R., et al. (författare) The effect of the polymerisation temperature on molecular weight and photoluminescence quantum yield for a phenylsubstituted PPV 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 119:1-3, s. 63-64 Tidskriftsartikel (refereegranskat)abstract We present the synthesis and characterisation of poly(2-(2',5'-bis(2?-ethylhexyloxy)phenyl)-1, 4-phenylenevinylene) (BEHP-PPV) polymerised under different conditions. The photoluminescence efficiencies (?PL) in the solid state of BEHP-PPV obtained at 144°C and 0°C are 28% and 60%, respectively. Polymerisation temperatures below 0°C decreases the molecular weight without changing the photoluminescence efficiency to any large extent.
8.	Bantikassegn, W., et al. (författare) Proceedings of the International Conference on Science and Technology of Synthetic Metals Electronic properties of polypyrrole (polystyrene-sulphonate)/metal junctions 1993 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 55:1, s. 36-42 Tidskriftsartikel (refereegranskat)abstract The nature of polymer/metal interfaces is decisive for the operation of polymer based electronic devices. At such interfaces charge transport may be affected by barrier formation, or by formation of insulating interfaces of various types. We have prepared thin films of conducting polypyrrole doped with large polymeric anions of polystyrenesulphonate for studies in metal/polymer junctions. Aluminium and gold contacts are vacuum deposited to form metal/polymer/gold sandwich structures. The current-voltage characteristics show that the interface between polypyrrole and gold is ohmic with no current limitation. However, the aluminium/polypyrrole interface forms highly resistive and nonohmic contacts. Photoelectron spectroscopy using UV and X-ray photons reveals a decrease of the work function upon Al deposition, reactions between Al and the sulphonate anions, and immediate oxidation of the aluminium upon exposure to oxygen. These observations corroborate the interpretation that the current limitation found at Al/polypyrrole junctions is due to formation of insulating aluminium oxide, not excluding reactions between the metal and dopant. It is also pointed out that interfaces between reactive metals and polymers are prone to such oxide interface formation, considering the high diffusivity of oxygen in many polymers.
9.	Berggren, Magnus, et al. (författare) Controlling colour by voltage in polymer light emitting diodes 1995 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 71:1-3, s. 2185-2186 Tidskriftsartikel (refereegranskat)abstract We report electroluminescence using different substituted polythiophenes as the emitting mterial. Different substituents cause different sterical interacion which force the thiophene rings out of planarity. This results in different bandgaps. Colours from blue to near infrared have been demonstrated in electroluminescent devices. We also demonstrate voltage controlled electroluminescence using mixtures of these polymers.
10.	Berggren, Magnus, et al. (författare) Organic lasers based on Forster transfer 1997 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 91:1-3, s. 65-68 Tidskriftsartikel (refereegranskat)abstract The light amplification characteristics of organic guest-host systems with Forster transfer from absorbing small molecule hosts to dye/ polymer dopants are described. Such material systems are shown to be very promising for use in low-threshold organic lasers. A number of laser resonators have been experimentally realized with Forster gain media including microdisk, ring, spheroid, and distributed Bragg reflector lasers. (C) 1997 Elsevier Science S.A.
11.	Berggren, Magnus, et al. (författare) Polymer light-emitting diodes placed in microcavities 1996 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 76:1-3, s. 121-123 Tidskriftsartikel (refereegranskat)abstract The use of resonant optical microcavities to influence the emission properties of conjugated polymer light-emitting diodes (LEDs) is reported. The microcavities, which are built using metallic mirrors and polymeric spacers, incorporate polymer LEDs in between the mirrors. We report experimental results of polymer LEDs based on substituted polythiophenes. The effects include substantial narrowing of the spectral width of the emitted light, enhancement of the emission at the microcavity resonance, and coupling of two emission processes to different resonance modes in the same cavity.
12.	Birgerson, J., et al. (författare) Doped polymeric cathodes for PPV/Al based LEDs 2002 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 132:1, s. 57-61 Tidskriftsartikel (refereegranskat)abstract The effect of Li-doping in poly(para-phenylenevinylene) (PPV) based light emitting devices has been studied. In a standard structure with an indium tin oxide (ITO) anode, poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT-PSS)-layer and an active PPV-layer, the effects of a thin (around 1 Å) Li-layer and a thin layer, (50 Å), of a large bandgap polymer, poly(2,5-diheptyl-1,4-phenylene-alt-1,4-naphthylene) (P14NHP) between the PPV and the aluminum cathode have been studied in terms of IV-characteristics and efficiency. The Li-atoms dope the interfacial layer of the PPV as seen by photoelectron spectroscopy. A thin layer of Li improves the charge balance by decreasing the energy barrier for injection of electrons for the Al/Li/PPV/PEDOT-PSS/ITO device. The efficient electron injection originates from a Fermi level alignment between the doped polymer and the aluminum cathode, which reduces the energy barrier. A thin layer of the large bandgap polymer P14NHP, between the PPV and Al contact, increases the light output and efficiency by blocking the holes. In addition, it may also reduce the light quenching by moving the region of recombination away from the Al-contact. The addition of a Li-layer on top of P14NHP leads to an increase of the quantum efficiency, because of better electron injection. © 2002 Elsevier Science B.V. All rights reserved.
13.	Birgerson, J., et al. (författare) Electronic structure of some conjugated polymers for electron transport 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 122:1, s. 67-72 Tidskriftsartikel (refereegranskat)abstract The chemical and electronic structure of three different, strictly alternating copolymers, poly(2,5-diheptyl-1,4-phenylene-alt-1,4-naphthylene) (P14NHP), poly(2,5-diheptyl-1,4-phenylene-alt-2,6-naphthylene) (P26NHP) and poly(2,5-diheptyl-1,4-phenylene-alt-9,10-anthrylene) (P910AHP), have been studied by photoelectron spectroscopy and optical absorption spectroscopy. The experimental results have been analyzed using the results of quantum chemical calculations. In the geometrical structure of all three of the polymers there are large torsion angles between the phenylene unit and the naphthylene or anthrylene units. These large torsion angles lead to localization of the p-electron wave functions, and minimal conjugation along the polymer backbone. For all three polymers, the highest occupied molecular orbital is completely localized to the naphthylene or anthrylene unit. The frontier molecular orbital wave functions are very reminiscent of the highest occupied orbitals of the isolated naphthalene or anthracene molecules. The optical absorption spectra of all three polymers verify the existence of large optical band gaps, consistent with the large torsion angels. The first several optical transitions in the polymers are also very reminiscent of the transitions in single naphthalene and anthracene molecules.
14.	Bolognesi, A., et al. (författare) High photoluminescence efficiency in substituted polythiophene aggregates 2003 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 139:2, s. 303-310 Tidskriftsartikel (refereegranskat)abstract In this paper we discuss the optical (absorption and photoluminescence) and solvatochromic properties of a newly synthesized alternating copolymer based on poly(3-alkylthiophene) structure. In this copolymer an unsubstituted thiophene ring is linked to a 3-alkyl-substituted thiophene, the two repeating units being alternated in the copolymer chains. Moreover, a bulky group, THP, with high steric hindrance has been introduced in the side chain. This copolymer, designed to preserve the backbone planarity of polythiophenes and to prevent a close packing arrangement through the non-regioregular insertion of the bulky substituted monomer, shows high PL quantum yield in the solid state and in solution aggregates. The electroluminescence of this copolymer is reported for a simple single layer device. © 2003 Elsevier Science B.V. All rights reserved.
15.	Bröms, P., et al. (författare) Optical absorption studies of sodium doped poly(cyanoterephthalylidene) 1994 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 67:1-3, s. 93-96 Tidskriftsartikel (refereegranskat)abstract The effects of doping poly(cyanoterephthalylidene) with sodium in ultrahighvacuum been studied by optical absorption spectroscopy. Upon doping, new optical transitions are observed within the bandgap; the characteristics of these transitions are consistent with the formation of bipolarons. The optical absorption results are confirmed by direct measurements of the doping-induced gap states using ultraviolet photoelectron spectroscopy.
16.	Dannetun, Per, et al. (författare) Interface formation between poly(2,5-diheptyl-p-phenylenevinylene) and calcium : implications for light-emitting diodes 1994 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 67:1-3, s. 133-136 Tidskriftsartikel (refereegranskat)abstract The early stages of metal/polymer interface formation between calcium and poly(2,5-diheptyl-p-phenylenevinylene) (PDHPV) have been studied using both X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Charge transfer is observed from the metal atoms to the polymer; as a result the calcium atoms at the interface are ionic, and negative bipolarons appear as the charge-carrying species on the polymer chains. This n-type doping of PDHPV by calcium leads to the appearance of new electronic states in the polymer bandgap. The calcium atoms appear to diffuse into the near surface region of the polymer, rather than forming a well-defined overlayer on the organic films.
17.	Dannetun, Per, et al. (författare) Proceedings of the International Conference on Science and Technology of Synthetic Metals The chemical and electronic structure of the interface between aluminum and conjugated polymers or molecules 1993 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 55:1, s. 212-217 Tidskriftsartikel (refereegranskat)abstract The interaction between aluminum and Î±-Ï‰-diphenyltetradecaheptaenee (DP7), Î±-sexithienyl (6T), and poly(p-phenylenevinylene) (PPV), respectively have been studied using both X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS). The UPS valence band spectra, are interpreted with the help of quantum chemical calculations based upon Modified Neglect of Diatomic Overlap (MNDO), Valence Effective Hamitonian (VEH) and ab initio Hartree-Fock methods. DP7 is a model molecule for polyacetylene, while 6T is a model molecule (an oligomer) of polythiophene. The results indicate that aluminum reacts strongly with the surfaces of all of the materials studied. The Ï€-electronic structure of each material was strongly modified. Furthermore, aluminum reacts preferentially with the polyene partof DP7, with the vinylene part of PPV, and with the Î±-carbons of the thiophene nits of 6T.
18.	Dannetun, P., et al. (författare) The eletronic structure of emeraldine doped in situ from HCl in the gas phase as studied by photoelectron spectroscopy 1991 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 41:1-2, s. 645-648 Tidskriftsartikel (refereegranskat)abstract The chemical and electronic structure of spin-coated films of polyaniline in the emeraldine state, treated in-situ with HCl in the gas phase, have been studied for the first time by means of X-ray Photoelectron Spectroscopy (XPS) and Ultra-violet Photoelectron Spectroscopy (UPS). Ultra thin films, of about several hundreds of Ã…ngstrÃ¶ms thickness, were spin-coated from a solution of chemically prepared emeraldine in NMP, onto substrates of aluminum or silicon. The salt forms were prepared both by (a) â€œwetâ€ doping in 1M HCl and (b) the in-situ treatment of the films with HCl in the gas phase. With XPS three different types of chlorine have been observed, two ionic and one covalent. With UPS the valence band spectra of the doped and undoped state, are studied.
19.	Dannetun, Per, et al. (författare) The evolution of charge-induced gap states in degenerate and non-degenerate conjugated molecules and polymers as studied by photoelectron spectroscopy 1994 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 67:1, s. 81-86 Tidskriftsartikel (refereegranskat)abstract We report the results of ultraviolet photoelectron spectroscopy (UPS) studies of the interaction between sodium and conjugated systems for a series of diphenylpolyees and diffrent oligomers of poly(p-phenylenevinylene) (PPV). The diphenylpolyenes include molecules containing two (i.e., stilbene) to 14 carbon atoms in the polyene part; stilbene itself can also be considered as a phenyl-capped monomer of PPV. Furthermore, a PPV oligomer with three phenylene units, as well as PPV itself, has been studied. The experimental results are interpreted with the help of quantum-chemical calculations using the Hartree-Fock semi-empirical Austin Model 1 (AM1) and valence-effective Hamiltonian (VEH) methods. An important result is that all the systems react strongly with sodium; at high doping levels two new doping-induced states are detected above the valence band edge of the pristine material. In the case of saturation-doped diphenylpolyenes (i.e., two sodiums per molecule), the new states can be discussed in terms of soliton-antisoliton pairs confined within the polyene part of the molecules; in contrast, the self-localized states induced in PPV and its oligomers have to be referred to as bipolarons.
20.	Ding, L., et al. (författare) Photovoltaic cells with a conjugated polyelectrolyte 2000 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 110:2, s. 133-140 Tidskriftsartikel (refereegranskat)abstract We describe photovoltaic cells made from a novel conjugated polyelectrolyte, the lithium salt of poly(thiophene-3-acetic acid) (PTAA-Li). The aqueous solubility of this polyelectrolyte allows formation of blend electrodes with a dispersion of the metallic polymer Poly(Ethylene DiOxyThiophene) (PEDOT). The incident monochromatic photon to current conversion efficiency (IPCE) of the cells were improved up to 19% by blending PTAA-Li with PEDOT to modify the ITO electrode, in combination with the low bandgap polymer poly(3-(4-octylphenyl)thiophene) (POPT), and C60 as electron acceptor. We attribute the increase of efficiency to the improved contact area between the conjugated polyelectrolyte and PEDOT.
21.	Edman, Ludvig, 1967-, et al. (författare) Influence of the anion on the kinetics and stability of a light-emitting electrochemical cell 2003 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 138:3, s. 441-446 Tidskriftsartikel (refereegranskat)abstract The selection of the anion is shown to be crucial for the response time and the lifetime of light-emitting electrochemical cells (LECs) fabricated with [co-block phenyl-substituted poly(para phenylene vinylene)]-PEO-LiX (X = Tf, TFSI, Tf-TFSI). With a mixed-anion (X = Tf-TFSI) salt. the LEC turned on in less than 0.4 s at ΔU = 4.0 V, with X = TFS1 it turned on in a few seconds, while X = Tf produced devices with significantly larger response times with a strong dependence on the film thickness. We attribute this significant variation in the response to the morphology of the PEO-LiX phase at room temperature: PEO-LiTf is largely crystalline with a correspondingly limited ionic mobility: PEO-LiTf-TFSI is amorphous with a relatively high mobility; and heat-treated PEO-LiTFSI is typically partially amorphous. For lifetimes. we focused on 3.0 ≤ ΔU ≤ 4.0 V since this range coincided with a crossover in performance for the X = Tf devices. At ΔU = 3.0 V, these lasted the entire measurement cycle (=55 h) with constant efficiency and only a small decrease in light output. At ΔU ≥ 3.25 V. the same devices exhibited a limited lifetime with a linear dependence on the salt concentration and a decrease in the efficiency with time. For X = TFSI. Tf-TFSI short lifetimes and a decrease in efficiency with time were obtained independent of the applied voltage. Considering recently published data on electrochemical stability, we propose that an irreversible overreduction of the anion is a significant side reaction that limits the lifetime of LEC systems.
22.	Fredriksson, C., et al. (författare) Theoretical studies of the aluminum/poly(p-phenylene vinylene) interface 1993 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 57:2, s. 4632-4637 Tidskriftsartikel (refereegranskat)abstract A molecular quantum chemical approach is used to study the aluminum on PPV (Poly(p-Phenylene Vinylene)) interface. We focus on modifications to the chemical and electronic structure of the polymer upon interaction with a submonolayer of aluminum. A model system, trans-stilbene, is taken to investigate the nature of the Al-PPV bonding. Energetically favorable conformations are then used as prototypes to study the evolution of the electronic structure as modified by the reaction with aluminum. Results at the ab initio Hartree-Fock level indicates that Al atoms react with the vinylene linkage rather than the phenyl groups at early stages of interface formation.
23.	Fredriksson, C., et al. (författare) Theoretical studies of the aluminum/trans-polyacetylene interface : Calculations of model systems and comparison to experiment 1993 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 57:2-3, s. 4590-4595 Tidskriftsartikel (refereegranskat)abstract The interaction between Al atoms and trans-polyacetylene has been studied quantum chemically at the ab initio Hartree-Fock level using oligomeric model systems. Investigations of the Al-polyacetylene bonding and modifications to the chemical and electronic structure of model systems for polyacetylene upon interaction with Al atoms are reported. The density-of-states is calculated for a polyene chain interacting with a pair of Al atoms. The results are discussed in relation to photoelectron spectra taken during Al deposition on an oligomeric model for polyacetylene (a diphenylpolyene with 7 C=C bonds in the polyene segment).
24.	Ghosh, S., et al. (författare) Nano-structured conducting polymer network based on PEDOT-PSS 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 121:1-3, s. 1321-1322 Tidskriftsartikel (refereegranskat)abstract Poly(3,4-ethylenedioxythiophene)-polystyrenesulphonate (PEDOT-PSS) has been crosslinked into network morphology. The morphologies of different crosslinked PEDOT-PSS firms have been characterised by atomic force microscopy (AFM). The crosslinked polymer shows highly efficient and fast redox activity, both in aqueous and non-aqueous media.
25.	Gigli, G., et al. (författare) A novel electroluminescent oligothiophene 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 119:1-3, s. 581-582 Tidskriftsartikel (refereegranskat)abstract We report investigations of the photoluminescence (PL) and electroluminescence (EL) of a novel substituted thiophene oligomer. The high PL efficiency in solid state (23%), the high electron affinity, together with the good processability make this material competitive for applications in organic emitting diodes (LEDs). EL efficiency of 0.1% is demonstrated in a stable LED with spin coated active layer.
26.	Granlund, Thomas, et al. (författare) Lasing in substituted polythiophene between dielectric mirrors 1999 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 102:1-3, s. 1038-1041 Tidskriftsartikel (refereegranskat)abstract We report photopumped lasing in a microcavity device with a polythiophene layer as emitter. The microcavity is made of a polymer film between two dielectric Bragg reflecting mirrors (DBR). The:microcavity devices is built by joining two polymer coated DBR mirrors at elevated temperature. When photopumping the film,a lasing threshold is observed at 120 nJ/cm(2). Comparative studies with fast pump-probe spectroscopy of thin polythiophene films, and the same polymer in photopumped lasing studies, indicate that the gain coefficient is 80 +/- 20 cm(2) and that the exciton concentration is 2X10(17) cm(2) at the lasing transition, well below the exciton-exciton recombination level.
27.	Granström, Magnus, et al. (författare) Phase separation of conjugated polymers - Tools for new functions in polymer LEDs 1997 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 85:1-3, s. 1193-1194 Tidskriftsartikel (refereegranskat)abstract Within the single family of substituted poly(thiophenes) it is possible to realize such diverse device designs as voltage controlled colours from polymer LEDs, sub-micron size LEDs, and white light emitters. Many of these features become possible by the use of polymer blends in which one or more poly(thiophenes) are mixed with a matrix polymer (PMMA). The phase structure in these blends can be controlled by stoichiometry and mode of formation. That phase structure can be used to prevent exciton transfer, and to define new colours in polymer LEDs. It also allows us to make anisotropic conductors suitable for contacting optical devices.
28.	Granström, Magnus, et al. (författare) Polymeric light-emitting diodes of submicron size - Structures and developments 1996 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 76:1-3, s. 141-143 Tidskriftsartikel (refereegranskat)abstract Micron- and submicron-sized light-emitting diodes (LEDs) made using conjugated polymers as electroluminescent layers and contact materials are presented. Two different routes to make arrays of such small light sources have been developed. The benefits and drawbacks of the use of the conjugated polymer poly(2,3-ethylene-dioxythiophene) (PEDOT) as hole injector in polymer LEDs are also discussed.
29.	Greczynski, G., et al. (författare) Hybrid interfaces in polymer-based electronics 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 121:1-3, s. 1625-1628 Tidskriftsartikel (refereegranskat)abstract Sandwich-style interfaces of Al/LiF/poly(9,9-dioctyl-fluorene) and A1/CsF/poly(9,9-dioctyl-fluorene) have been studied using X-ray and ultraviolet photoelectron spectroscopy. In the case of LiF-deposition on poly(9,9-dioctyl-fluorene) films, doping did not occur, nor did the LiF dissociate upon Al-deposition. No significant shifts in binding energy of the core levels, or any changes in the work function were detected. However, for the Al/LiF/poly(9,9-dioctyl-fluorene) interface, there was no degradation of the p-electronic structure, unlike the case for Al deposited directly unto poly(9,9-dioctyl-fluorene). For the Al/CsF/poly(9,9-dioctyl-fluorene) interface, the CsF dissociated upon Al deposition, with the Cs likely n-doping the polymer at the interface. When deposited onto an Al surface, CsF also was found to dissociate at the interface but remaining in the CsF form away from the Al surface. Vacuum level alignment occurs for poly(9,9-dioctyl-fluorene) films spun onto 'metal' substrates. The hole-injection barrier in poly(9,9-dioctyl-fluorene)-based LEDs is hence determined by the difference between anode work function and the polymer ionization potential.
30.	Hellberg, Jonas, et al. (författare) New monomers for polythiophenes 1997 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 84, s. 251-252 Tidskriftsartikel (refereegranskat)abstract Two series of chalcogen substituted thiophene monomers have been synthesised; 3-(4-alkylchalcogenophenyl)thiophenes 1a-c and 3-(4-alkylphenylchalcogeno)thiophenes 2a-d. Polymerisations of examples of these with iron(III)chloride gave regiorandom polymers. Light-emitting diodes with low efficiency could be fabricated from poly-1a and poly-1b.
31.	Hjort, M., et al. (författare) Localization in defected chiral carbon nanotubes 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 121:1-3, s. 1239-1240 Tidskriftsartikel (refereegranskat)abstract Defects in metallic carbon nanotubes have been studied within the tight binding model using the transfer matrix approach. A newly developed method for obtaining transfer matrices in a general way has been utilized, enabling us to compare nanotubes with various chiralities. The localization length was calculated for a random disorder in the onsite potentials, as well as for a functionalization type of disorder.
32.	Inganäs, Olle, et al. (författare) Recent progress in thin film organic photodiodes 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 121:1-3, s. 1525-1528 Tidskriftsartikel (refereegranskat)abstract We review current developments in organic photodiodes, with special reference to multilayer thin film optics, and modeling of organic donor-acceptor photodiodes. We indicate possibilities to enhance light absorption in devices by nanopatterning as well as by blending, and also discuss materials science issues of nanostructure in blends and in vertically stratified multilayer devices. Our current best devices have external efficiencies of 30-50% in between 400-600 nm, and show fill factors of 0.54 illuminated under weak monochromatic light.
33.	Inganäs, Olle, et al. (författare) Thiophene polymers in light emitting diodes : Making multicolour devices 1995 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 71:1-3, s. 2121-2124 Tidskriftsartikel (refereegranskat)abstract We can control the bandgap of thiophene polymers over 2 eV by choosing the nature, position and regularity of side chain substitutions. Electroluminescence from these polymers cover the full visible spectrum, from the blue into the near infra-red. Blends of these polymer materials allow us to construct voltage controlled variable colour light sources. A newly developed transfer technique allow us to mount thin oriented films of the polymers in polymer LEDs to obtain polarised light sources giving polarisation anisotropys of up to 3. Sub-lambda light sources have been constructed from these polymer materials using nanometer polymer electrodes.
34.	Johansson, A., et al. (författare) Polaron dynamics in a system of coupled conjugated polymer chains 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 119:1-3, s. 235-236 Tidskriftsartikel (refereegranskat)abstract Motion of excitations such as solitons and polarons are of fundamental importance for the electron/hole transport properties of conjugated polymers for the use in, e.g., polymer based LED's. Polaron dynamics in coupled polymer chains in the presence of an external electric field, has been investigated theoretically using the SSH-model. In particular we focus on how a polaron migrates through the polymer lattice, i.e. the situation in which a polaron reaches a chain end and is scattered to the surrounding chains.
35.	Johansson, D.M., et al. (författare) Convenient synthetic route to poly(p-phenylene-1,2-diphenylvinylenes) 2000 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 113:3, s. 293-297 Tidskriftsartikel (refereegranskat)abstract The synthesis and characterization of two soluble poly(p-phenylenevinylene)s substituted with phenyl groups on the vinylene moiety is reported. The polymers are poly(1,4-phenylene-1,2-diphenylvinylene) (PPV-DP) and poly(1,4-phenylene-1,2-(3'-(2?-ethylhexyloxy))-diphenylvinylene) (PPV-mEHDP). The monomers containing chloromethyl groups were polymerized with excess potassium tert-butoxide in dioxane at room temperature. The polymerization conditions are optimized. The photoluminescence (PL) properties of the polymers showed an increase in the PL efficiency in film from 19% for PPV-DP to 37% for PPV-mEHDP. Both polymers emitted green light with higher intensity in film than in solution.
36.	Johansson, D.M., et al. (författare) Synthesis and characterisation of polyfluorenes with light-emitting segments 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 121:1-3, s. 1761-1762 Tidskriftsartikel (refereegranskat)abstract We present the synthesis and characterisation of two copolymers. They consists of poly(9-hexyl-9-(2'-ethylhexyl)fluorene) (HEH-PF) with a small amount of another polymer with a narrow band-gap. The synthetic route was designed to allow the incorporation of only one low band-gap segment per polymer chain. Photoluminescence measurements showed that energy transfer from the PF-segments to the low band-gap segments, did occur. In the solid state, all emissions were detected from the low band-gap segments with photoluminescence quantum yields up to 68%. One copolymer showed a low threshold for lasing (2 µJ/cm2) in a microcavity device.
37.	Johansson, Tomas, et al. (författare) Conductivity of de-doped poly(3,4-ethylenedioxythiophene) 2002 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 129:3, s. 269-274 Tidskriftsartikel (refereegranskat)abstract The conductivity of chemically and electrochemically de-doped poly(3,4-ethylenedioxythiophene) (PEDOT) has been investigated in situ. We observe a decrease in the conductivity by 4-5 orders of magnitude. The change of conductivity is correlated to the change of electronic structure. We obtain the dielectric function of the polymer by spectroscopic ellipsometry and note that anisotropy is observed in both doped and neutral states. © 2002 Elsevier Science B.V. All rights reserved.
38.	Jonforsen, M., et al. (författare) Photodiodes made from poly(pyridopyrazine vinylene) : polythiophene blends 2001 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 119:1-3, s. 185-186 Tidskriftsartikel (refereegranskat)abstract A PPV-type polymer with the pyridopyrazine heterocycle (EHH-PPyPzV) has been synthesised and found to have high electron affinity according to electrochemical measurements. When used as the electron accepting material in single-layer-photodiodes, with a thiophene copolymer (PEOPT-co-PAAPT) as the electron donating material, IPCE (incident photon to current conversion efficiency) up to 1% was measured. Atomic force microscopy was used to analyse the blend morphology in the devices.
39.	Jonforsen, M., et al. (författare) Synthesis and characterization of poly(quinoxaline vinylene)s and poly(pyridopyrazine vinylene)s with phenyl substituted side-groups 2002 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 131:1-3, s. 53-59 Tidskriftsartikel (refereegranskat)abstract Poly(quinoxaline vinylene) and poly(pyridopyrazine vinylene) with 3(2'-ethylhexyloxy)phenyl side-groups have been synthesized and compared with similar polymers with purely aliphatic side-chains. The new polymers had smaller bandgaps, and from cyclic voltammetry it was seen that the phenyl substituted side-groups made the polymers easier to reduce, with half wave potentials of -1.02 and -1.33 V versus Ag/AgCl for the poly(pyridopyrazine vinylene) and poly(quinoxaline vinylene) respectively. The attachment of the phenyl substituted side-groups had counteracting effects on the stability towards photo-oxidation, which resulted in improved stability of the poly(pyridopyrazine vinylene) compared to its equivalent with purely aliphatic side-chains, while the poly(quinoxaline vinylene) showed decreased stability. © 2002 Elsevier Science B.V. All rights reserved.
40.	Jönsson, Stina, et al. (författare) The effects of solvents on the morphology and sheet resistance in poly(3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT–PSS) films 2003 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 139:1, s. 1-10 Tidskriftsartikel (refereegranskat)abstract Films of poly(3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT–PSS), prepared by coating the aqueous PEDOT–PSS dispersion and by coating a mixture of the PEDOT–PSS dispersion and different solvents, have been studied using four-point probe conductivity measurements, atomic force microscopy and photoelectron spectroscopy. The electrical conductivity of thin films of the second type (further on called PEDOT–PSS–solvents) was increased by a factor of about 600 as compared to films of the first type (further on called PEDOT–PSS–pristine). Morphological and physical changes occur in the polymer film due to the presence of the solvent mixture, the most striking being that the ratio of PEDOT-to-PSS in the surface region of the films is increased by a factor of ∼2–3. This increase of PEDOT at the surface indicates that the thickness of the insulating PSS ‘shell’ that surrounds the conducting PEDOT–PSS grains is reduced. The (partial) reduction of the excess PSS layer that surrounds the conducting PEDOT–PSS grains is proposed to lead to an increased and improved connectivity between such grains in the film and hence a higher conductivity. When PEDOT–PSS–solvents receives a post-coating heat treatment, the increased PEDOT-to-PSS ratio at the surface is maintained or even slightly improved, as is the increase in electrical conductivity, even though spectroscopy show that the solvent molecules are removed. This suggests that screening or doping by the solvents throughout the film are not likely to be the key mechanisms for the improved conductivity and supports our proposed mechanism of improved conductivity through improved connectivity between the conducting grains.
41.	Kaminorz, Y., et al. (författare) Characteristics of polythiophene surface light emitting diodes 2000 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 113:1, s. 103-114 Tidskriftsartikel (refereegranskat)abstract Surface light emitting diodes (SLEDs), in which previously microfabricated electrodes were coated with a conjugated polymer, were made with greatly different electrode spacings (250 nm and 10 or 20 µm) and with different electrode material combinations. The fabrication process allowed us to compare several electrode materials. The SLED structures also enabled imaging of the light emission zone with fluorescence video microscopy. Conventional sandwich structures were also made for comparison (electrode separation 50 nm). In this study, the emitting layer was poly[3-(2',5'-bis(1?,4?,7?trioxaoctyl)phenyl)- 2,2'-bithiophene] (EO-PT), a conjugated polymer based on polythiophene with oligo(ethyleneoxide) side chains. The current-voltage (I(V)) and light-voltage (L(V)) characteristics of the SLEDs were largely insensitive to electrode separation except at high voltages, at which the current in the devices with the largest separations was limited. Sandwich structures had the same light output at a given current. Light could be obtained in forward and reverse bias from indium tin oxide (ITO)-aluminum, gold silicide-aluminum, and gold silicide-gold SLEDs, but the turn-on voltages were lowest with the ITO-aluminum devices, and these were also the brightest and most reliable. Adding salt to the EO-PT increased the current and brightness, decreased the turn-on voltages, and made the I(V) characteristics symmetric, thus, a device with an electrode separation of 10 µm had the extraordinarily low turn-on voltage of 6 V. The location of the light emission was at the electron-injecting contact.
42.	Kim, J.S., et al. (författare) Kelvin probe and ultraviolet photoemission measurements of indium tin oxide work function: : a comparison 2000 Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 111-112, s. 311-314 Tidskriftsartikel (refereegranskat)abstract We report a comparison of the work functions of thin films of indium tin oxide (ITO), carried out by means of ultraviolet photoelectron spectroscopy (UPS) and by measurements of the contact potential difference with respect to a gold reference electrode (Kelvin probe (KP) method). We investigated commercially available ITOs both "as-received", and after certain surface treatments, such as oxygen plasma. First, we find measurable discrepancies between KP values measured with three different instruments, and between the KP and the UPS values. Secondly, and unexpectedly, we find that the KP, although more sensitive than UPS, does not detect certain differences between ITOs with different surface treatments. We discuss the results in view of the different environments in which the measurements are carried out (UHV for the UPS and air/Ar for the Kelvin method), of the effects which may be induced by the high-energy photon irradiation in the UPS measurement, and of the stability of the gold probe work function in gas ambient. We conclude that UPS is better-suited for absolute work function determination, although KP remains a convenient and inexpensive tool for fast screening of contact potential differences. (C) 2000 Elsevier Science S.A. All rights reserved.
43.	Lazzaroni, R., et al. (författare) Chemical and electronic aspects of metal/conjugated polymer interfaces : Implications for electronic devices 1995 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 71:1-3, s. 2159-2162 Tidskriftsartikel (refereegranskat)abstract The chemical nature and the electronic structure of metal/conjugated polymer interfaces are investigated in the context of polymer-based light-emitting diodes. We consider the interaction of low-workfunction metals (Al, Ca) with the surface of conjugated polymers or model oligomer molecules with a combined experimental and theoretical approach. The early stages of the interface formation are followed with X-ray and ultraviolet photoelectron spectroscopies and the experimental data are compared to the results of quantum chemical calculations. The reactions of Al and Ca with the organic surface are found to be fundamentally different: while the former forms new covalent bonds onto the polymer backbone, the latter tends to dope the conjugated system. Both types of reaction are expected to modify drastically the electronic properties of the polymer semiconductor.
44.	Lazzaroni, R., et al. (författare) Electronic structure of the aluminum/polythiophene interface : A joint experimental and theoretical study 1991 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 43:1-2, s. 3323-3328 Tidskriftsartikel (refereegranskat)abstract Not Available.
45.	Lundberg, Bo, et al. (författare) Pressure, temperature and field dependence of hopping conduction in polyaniline 1987 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 21:1-3, s. 143-147 Tidskriftsartikel (refereegranskat)abstract The electrical resistance of the emeraldine salt form of polyaniline has been measured under variable pressure (0 – 1 GPa), temperature (80 – 300 K) and electric field strength (0 – 80 V/cm). The temperature dependence fits σ = σo exp(-(T0/T)1/2), which indicates one-dimensional variable range hopping or three-dimensional fluctuation-induced tunnelling. A large linear compressibility, indicating a fibrous structure in polyaniline, favours hopping conduction. The maximum field strength was, however, far too small to allow discrimination between the two models.
46.	Lundin, Anders, et al. (författare) Density of state variation in polypyrrole as a function of pressure up to 1.5 GPa 1990 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 39:2, s. 233-242 Tidskriftsartikel (refereegranskat)abstract The electrical resistance (temperature and pressure dependence) and room temperature compressibility measurements for electrochemically synthesized polypyrrole are reported. We find that in this relatively highly conducting (20 S cm−1) polymer the conducting mechanism is governed by variable range hopping. From the pressure dependence of Mott's parameter, To, corrected for by compressibility data, the density of localized states at the Fermi level can be evaluated and has been found to increase by about 70% up to 1.5 GPa. From the experimental data of resistance and compressibility, β, we derive an expression for the pressure dependence of the conductivity, σ(P) = σ(T)(1 + βP) exp[(P/Po)n], where n≅34.
47.	Lögdlund, Michael, et al. (författare) A photoelectron spectroscopy study of the charge-induced π-electronic structural changes in α.ω.-diphenyltetradecaheptaene, a model molecule for polyacetylene 1993 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 57:2, s. 4722-4727 Tidskriftsartikel (refereegranskat)abstract The π€-electronic structural changes in diphenylpolyene, α.ω.-diphenyltetradecaheptaene, or DP7, have been studied upon gradually doping with sodium Xu using X-ray and Ultraviolet Photoelectron Spectroscopy, XPS and UPS. The spectra are interpreted with the help of the results from Austin Model 1 (AM1) and Valence Effective Hamiltonian (VEH) quantum chemical calculations. The results of the doping with sodium can be discussed in terms of two confined solitons on the polyene part of the molecule, which results in two new energy levels in the originally forbidden energy gap.
48.	Lögdlund, Michael, et al. (författare) The electronic structure of α,ω-diphenyltetradecaheptaene, a model molecule for polyacetylene, as studied by photoelectron spectroscopy 1992 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 51:1, s. 187-195 Tidskriftsartikel (refereegranskat)abstract The advantages of using model systems for spectroscopic studies of conjugated polymers and interface formation, as well as for charge-induced electronic and geometric structural changes, are discussed. The electronic structure of a diphenylpolyene, Î±,Ï‰-diphenyltetradecaheptaene, or DP7, is an example of a model molecular system studied using X-ray and Ultraviolet Photoelectron Spectroscopy, XPS, and UPS. The spectra are interpreted with the help of the results from MNDO, VEH and INDO/S-CI quantum chemical calculations. The frontier orbitals of DP7 are localized mostly on the polyene chain portion of the molecule, resulting in a high degree of separation of the phenyl and polyene parts of the Ï€-system. The INDO calculations show two regions of shake-up features corresponding to a benzene-like part and a polyene-like part. The most important individual shake-up transitions, which contribute to the two observed shake-up spectral features, involve one-electron redistributions separable into contributions from the polyene chain and from the phenyl groups. The analysis indicates the extent to which many chemical and electronic properties of DP7 are expected to be similar to those of (at least short chain) trans-polyacetylene.
49.	Lögdlund, Michael, et al. (författare) Theoretical study of the interaction between sodium and oligomers of poly(p-phenylenevinylene) and poly(p-phenylene) 1994 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 67:1-3, s. 141-145 Tidskriftsartikel (refereegranskat)abstract The semi-empirical Austin Model 1 and the non-empirical pseudo-potential valence effective Hamiltonian (VEH) methods as well as the local spin density (LSD) approximation technique have been applied to the investigation of the doping-induced electronic and geometrical changes in some conjugated molecules related to poly(p-phenylene) and poly(p-phenylenevinylene) (PPV): biphenyl, stilbene and a phenyl-capped dimer of PPV. The theoretical results are compared with experimental valence band spectra, as recorded by ultraviolet photoelectron spectroscopy (UPS). The experimental UPS studies show that two ingap states are detected upon doping with alkali metals. The energy splitting between the two in-gap states increases as the molecule size decreases. The results of the LSD calculations agree very well with the experimental results, while the VEH method overestimates the energy splitting for the small molecules. The LSD modelling also indicates a destabilization of several high binding energy valence levels, due to the presence of counter-ions, in agreement with experiment.
50.	Nilsson, K.Peter R., et al. (författare) Conformational transitions in a free amino acid functionalized polythiophene 2003 Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 135-136, s. 291-292 Tidskriftsartikel (refereegranskat)abstract A chiral, 3-substituted polythiophene with an amino acid function shows pH-dependent visible, emission and circular dichroism spectra in buffered aqueous solution. At pH equal to pi of the amino acid, the backbone adopts a non-planar right-handed helical conformation and the polymer chains are separated from each other. Increasing pH leads to a more planar conformation of the backbone and an aggregation of the polymer chains occurs. A lower pH will also lead to a more planar conformation of the backbone, but aggregation of the polymer chains appears to be absent. © 2003 Elsevier Science B.V. All rights reserved.

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