| 61. |
- Nyberg, Tobias, et al.
(författare)
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Macromolecular nanoelectronics
- 2002
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Ingår i: Current applied physics. - 1567-1739 .- 1878-1675. ; 2:1, s. 27-31
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Tidskriftsartikel (refereegranskat)abstract
- We have explored new organic materials and fabrication methods to fabricate organic photodiodes and light emitting diodes. Grafting of a fullerene derivative to a polythiophene backbone yielded an integrated acceptor-donor polymer that we used as the active material in organic photodiodes. Using a method of soft lithography. soft embossing, we fabricated submicron structures to be used as organic light emitting diodes. Employing a silicone rubber replica (stamp) of an optical diffraction grating we transferred the grating pattern to an organic resist layer by placing the stamp in conformal contact with the resist. The transferred pattern was subsequently used as an etch mask for the processing of the device. The structures were successfully utilized as light emitting diodes and photodiodes, with device characteristics influenced by the imposed structure. (C) 2002 Published by Elsevier Science B.V.
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| 62. |
- Nyberg, Tobias, et al.
(författare)
-
Polymer hydrogel microelectrodes for neural communication
- 2002
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Ingår i: Biomedical microdevices (Print). - 1387-2176 .- 1572-8781. ; 4:1, s. 43-52
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Tidskriftsartikel (refereegranskat)abstract
- A conducting polymer hydrogel electrode was electrochemically deposited in micromachined via holes and the charge delivery capacity (CDC) was studied. Polymer hydrogel microelectrodes, with a geometric area of 1000 mum(2), and a capacitance of up to 850 nF were fabricated. The impedance of a 1,000 mum(2) polymer hydrogel electrode deposited with 8 muC was measured as low as 8.5 kOmega. We studied neural cell growth on structures to be used as neural interfaces. Directed cell growth was achieved by imposing a topographical structure on the substrate. Due to the interesting mechanical and chemical adaptability of the polymer hydrogel material and its large charge delivery capacity and low impedance we think that it is an interesting material for neural communication.
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| 63. |
- Nyberg, Tobias, et al.
(författare)
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Submicrometre bridge electrode arrays for light emitting polymer diodes and photodiodes
- 2002
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 13:2, s. 205-211
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Tidskriftsartikel (refereegranskat)abstract
- We have used a method of soft lithography, soft imprinting, to fabricate submicrometre structures to be used as light emitting polymer diodes and photodiodes. Using a silicone rubber replica (stamp) of an optical diffraction grating we transferred the grating pattern to an organic resist layer by placing the stamp in conformal contact with the resist. The transferred pattern was subsequently used as an etch mask for the processing of the device. This cheap and fast process, not limited by optical diffraction, was used to fabricate submicrometre structures over large areas, square millimetres. The structures were successfully utilized as light emitting diodes and photodiodes, with device characteristics influenced by the imposed structure.
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| 64. |
- Persson, Nils-Krister, et al.
(författare)
-
Optical modelling of a layered photovoltaic device with a polyfluorene derivative/fullerene as the active layer
- 2004
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 83:2-3, s. 169-186
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Tidskriftsartikel (refereegranskat)abstract
- Here we report on optical modelling of organic photovoltaic devices having a layered geometry, with polyfluorene-copolymer as the active material and C60 as the acceptor. Thin film theory in a matrix formalism enables analysis of the impact of reflection and interference on the optical electric field. The model allows us to predict an optimal C60 thickness where concern has been taken for light being both polychromatic and distributed according to solar irradiation. Fundamental for light–matter interaction is the dielectric function. We have extracted it for two variants of a new polyfluorene copolymer, PFDTBT, from UV via visible to the nearest infrared, using spectroscopic ellipsometry (SE). n is found to be relatively high with a max-value above 2.1. The process of spin coating induces anisotropy in the polymer film.
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| 65. |
- Pettersson, Fredrik, et al.
(författare)
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Surface micromachined polymer actuators as valves in PDMS microfluidic system
- 2000
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Ingår i: 1st Annual International, Conference On Microtechnologies in Medicine and Biology. 2000. - : IEEE. - 0780366034 ; , s. 334-335
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Konferensbidrag (refereegranskat)abstract
- To control flows in microfluidic systems there is a need of valves. Desirable properties of such valves are in general low cost, low dead-volume, fast response and low power-consumption. For bioanalytical purposes the requirements also include biocompatibility and ability to function in biological fluids. One way to address these problems is to use surface-fabricated actuators, and then bonding the actuator chip with high aspect-ratio flow-channels in a thick polymer cover. A suitable cover structure can be made in elastomeric poly(dimethylsiloxane) (PDMS) which can be joined to a silicon surface. The active valve structures can be micromuscles, i.e. actuators based on conjugated polymer such as polypyrrole (PPy), which can be electrochemically doped. The reversible doping of PPy forces counterions to flow into or out of the polymer to balance the charge, resulting in a volume change. This volume change can be used in a bilayer actuator, where a metal can serve as constant volume layer as well as electrical contact to the polymer layer changing volume under reversible doping
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| 66. |
- Pettersson, Lars, et al.
(författare)
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Optical anisotropy in thin films of poly(3,4-ethylenedioxythiophene)- poly(4-styrenesulfonate)
- 2002
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Ingår i: Organic electronics. - 1566-1199 .- 1878-5530. ; 3:3-4, s. 143-148
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropic optical constants spectrum of spin-coated thin films of poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate) (PEDOT-PSS) from 200 to 1700 nm were determined using variable-angle spectroscopic ellipsometry and polarized intensity transmission data together with absorption spectroscopy. PEDOT-PSS was found to be very anisotropic, uniaxial with the optic axis parallel to the surface normal. The result is in good agreement with results obtained of chemically polymerized PEDOT layers doped with toluenesulfonate. By adding sorbitol to the PEDOT-PSS dispersion before spin-coating, layers with a higher conductivity were obtained. A detailed study was made of the optical response of these layers in comparison to the PEDOT-PSS prepared from dispersions without sorbitol. The optical anisotropy is important to consider when using PEDOT-PSS in optoelectronic devices, such as polymer light-emitting diodes and photovoltaic devices. © 2002 Elsevier Science B.V. All rights reserved.
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| 67. |
- Pettersson, Lars, et al.
(författare)
-
Quantum efficiency of exciton-to-charge generation in organic photovoltaic devices
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89:10, s. 5564-5569
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Tidskriftsartikel (refereegranskat)abstract
- We present an analysis of the internal monochromatic quantum efficiency of photovoltaic devices based on polymer and polymer/fullerene thin films. A quantum efficiency of exciton-to-charge generation is defined as the external monochromatic quantum efficiency normalized to the absorption in the active materials of the device. An upper limit of the efficiency can be determined, and results show that much of the light is absorbed in photoactive layers of the device, whereas only a fraction of the generated excitons is converted to charge carriers and can be collected as photocurrent. © 2001 American Institute of Physics.
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| 68. |
- Roman, LS, et al.
(författare)
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Photovoltaic devices based on photo induced charge transfer in polythiophene : CN-PPV blends
- 2003
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Ingår i: Brazilian journal of physics. - 0103-9733 .- 1678-4448. ; 33:2, s. 376-381
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the photovoltaic properties of polymer devices based on a blend of two polymers, (poly(3-(2'-methoxy-5'-octylphenyl) thiophene) (POMeOPT) and poly(2,5,2',5'-tetrahexyloxy-7,8'-dicyanodi-p-phenylenevinylene) (CN-PPV), where photo induced charge transfer takes place at the interfaces formed by the interpenetrating network of the donor and the acceptor. The polymer blend films resulting from the spin coating were phase separated and the photo response of the devices depended on the morphology of the segregation. We have studied different blend ratios by photoluminescence quenching, scanning force microscopy and photovoltaic measurements. External quantum efficiencies of 4.5% at 500nm were achieved for the less segregated polymer blend.
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| 69. |
- Roman, L.S., et al.
(författare)
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Charge carrier mobility in substituted polythiophene-based diodes
- 2001
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Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 125:3, s. 419-422
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the transport properties of the semiconducting polymer poly(3-(2'-methoxy-5'-octylphenyl)thiophene) (POMeOPT). We have measured the current-voltage (C-V) characteristics of single polymer layer devices in two regimes contact limited current and bulk-limited current. The passage from one regime to the other was done upon insertion of a conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT-PSS) between the metallic electrode and the semiconducting polymer. With PEDOT-PSS as electrode, the polymer gave space-charge limited current (SCLC) with the mobility dependent on electric field. Fitting the data, we were able to obtain important parameters, such as the zero-field mobility and the characteristic field. We have compared our results with the well-studied polymer poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) in similar experiments earlier reported. © 2001 Elsevier Science B.V. All rights reserved.
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| 70. |
- Roman, LS, et al.
(författare)
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Trapping light in polymer photodiodes with soft embossed gratings
- 2000
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Ingår i: Advanced Materials. - 0935-9648 .- 1521-4095. ; 12:3, s. 189-
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Tidskriftsartikel (refereegranskat)abstract
- Increasing the conversion efficiency is very important in photovoltaic devices, as is cheap and simple technology. Here is demonstrated a soft embossing technique for printing a submicrometer grating with an elastomeric mold into an optically active polymer layer in a photovoltaic device (see Figure). The light trapping due to the grating pattern enhances the photoconversion efficiency by more than 25 % at normal light incidence (see also inside front cover).
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