| 1. |
- Charrier, Dimitri S. H., et al.
(författare)
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Real versus measured surface potentials in scanning Kelvin probe microscopy
- 2008
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Ingår i: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 2:4, s. 622-626
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Tidskriftsartikel (refereegranskat)abstract
- Noncontact potentiometry or scanning Kelvin probe microscopy (SKPM) is a widely used technique to study charge injection and transport in (in)organic devices by measuring a laterally resolved local potential. This technique suffers from the significant drawback that experimentally obtained curves do not generally reflect the true potential profile in the device due to nonlocal coupling between the probing tip and the device. In this work, we quantitatively explain the experimental SKPM response and by doing so directly link theoretical device models to real observables. In particular, the model quantitatively explains the effects of the tip-sample distance and the dependence on the orientation of the probing tip with respect to the device.
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| 2. |
- Krebs, Frederik C, et al.
(författare)
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A round robin study of flexible large-area roll-to-roll processed polymer solar cell modules
- 2009
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Ingår i: SOLAR ENERGY MATERIALS AND SOLAR CELLS. - : Elsevier BV. - 0927-0248. ; 93:11, s. 1968-1977
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Tidskriftsartikel (refereegranskat)abstract
- A round robin for the performance of roll-to-roll coated flexible large-area polymer solar-cell modules involving 18 different laboratories in Northern America, Europe and Middle East is presented. The study involved the performance measurement of the devices at one location (Riso DTU) followed by transportation to a participating laboratory for performance measurement and return to the starting location (Riso DTU) for re-measurement of the performance. It was found possible to package polymer solar-cell modules using a flexible plastic barrier material in such a manner that degradation of the devices played a relatively small role in the experiment that has taken place over 4 months. The method of transportation followed both air-mail and surface-mail paths.
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| 3. |
- Lakhwani, Girish, et al.
(författare)
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Intensive Chiroptical Properties of Chiral Polyfluorenes Associated with Fibril Formation
- 2009
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society. - 1520-6106 .- 1520-5207. ; 113:43, s. 14047-14051
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of chiral poly {9,9-bis[(3S)-3,7-dimethyloctyl]-2,7-fluorene} (1) were studied using circular dichroism (CD) spectroscopy. Films spin coated from chloroform solution, show CD with a degree of polarization g(abs) (= +4 x 10(-4) at 400 nm) that is independent of film thickness (50-290 nm). This implies that gabs is an intensive property of the material and related to the chiral organization of the molecules on a length scale less than 50 nm. Atomic force microscopy (AFM) on the films reveals fibrils. Addition of nonsolvent methanol to a solution of 1 in chloroform leads to fibril formation in solution and results in CD similar in band shape to that of the pristine spin coated films from chloroform solution and a g(abs) comparable in magnitude. Thus the chiral molecular arrangement leading to circular dichroism is part of the internal structure of these fibrils.
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| 4. |
- Mantovani Nardes, Alexandre, et al.
(författare)
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A morphological model for the solvent-enhanced conductivity of PEDOT : PSS thin films
- 2008
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Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028. ; 18:6, s. 865-871
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Tidskriftsartikel (refereegranskat)abstract
- The well-known enhanced conductivity of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) thin films that is obtained by addition of high-boiling solvents like sorbitol to the aqueous dispersion used for film deposition is shown to be associated with a rearrangement of PEDOT-rich clusters into elongated domains, as evidenced from STM and AFM. Consistently, temperature dependent conductivity measurements for sorbitol-treated films reveal that charge transport occurs via quasi ID variable range hopping (VRH), in contrast to 3D VRH for untreated PEDOT:PSS films. The typical hopping distance of 60-90 nm, extracted from the conductivity measurements is consistent with hopping between the 30-40 nm sized grains observed with scanning probe microscopy.
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| 5. |
- Mantovani Nardes, Alexandre, et al.
(författare)
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Microscopic understanding of the anisotropic conductivity of PEDOT : PSS thin films
- 2007
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 19:9, s. 1196-
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Tidskriftsartikel (refereegranskat)abstract
- The amsotropic conductivity of thin films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is correlated to the film morphology as obtained from scanning tunneling and atomic force microscopy images. The material was found to consist of layers of flattened PEDOT-rich particles that are separated by quasi-continuous PSS lamella (see figure).
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| 6. |
- Mathijssen, Simon G. J., et al.
(författare)
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Charge trapping at the dielectric of organic transistors visualized in real time and space
- 2008
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 20:5, s. 975-
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Tidskriftsartikel (refereegranskat)abstract
- Scanning Kelvin probe microscopy demonstrates that water-induced charge trapping at the SiO2 dielectric visualized in real time and space - is responsible for the commonly observed gate-bias-induced threshold-voltage shift in organic field-effect transistors. When a bias is applied to the electrodes, charges are injected onto the SiO2 (see background of the figure). When the contacts are grounded, the charges are released again (foreground picture).
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| 7. |
- Mathijssen, Simon G. J., et al.
(författare)
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Manipulating the local light emission in organic light-emitting diodes by using patterned self-assembled monolayers
- 2008
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 20:14, s. 2703-
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Tidskriftsartikel (refereegranskat)abstract
- Patterned organic light-emitting diodes are fabricated by using microcontactDrinted self-assembled monolayers on a gold anode (see background figure). Molecules with dipole moments in opposite directions result in an increase or a decrease of the local work function (foreground picture), providing a direct handle on charge injection and enabling local modification of the light emission
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| 8. |
- Mathijssen, Simon G. J., et al.
(författare)
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Monolayer coverage and channel length set the mobility in self-assembled monolayer field-effect transistors
- 2009
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Ingår i: Nature Nanotechnology. - : Nature Publishing Group. - 1748-3387 .- 1748-3395. ; 4:10, s. 674-680
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Tidskriftsartikel (refereegranskat)abstract
- The mobility of self-assembled monolayer field-effect transistors (SAMFETs) traditionally decreases dramatically with increasing channel length. Recently, however, SAMFETs using liquid-crystalline molecules have been shown to have bulk-like mobilities that are virtually independent of channel length. Here, we reconcile these scaling relations by showing that the mobility in liquid crystalline SAMFETs depends exponentially on the channel length only when the monalayer is incomplete. We explain this dependence both numerically and analytically, and show that charge transport is not affected by carrier injection, grain boundaries or conducting island size. At partial coverage, that is when the monolayer is incomplete, liquid-crystalline SAMFETs thus form a unique model system to study size-dependent conductance originating from charge percolation in two dimensions.
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| 9. |
- Maturova, Klara, et al.
(författare)
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Scanning Kelvin Probe Microscopy on Bulk Heterojunction Polymer Blends
- 2009
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Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlag. - 1616-301X .- 1616-3028. ; 19:9, s. 1379-1386
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Tidskriftsartikel (refereegranskat)abstract
- Here, correlated AFM and scanning Kelvin probe microscopy measurements with sub-100 nm resolution on the phase-separated active layer of polymer-fullerene (MDMO-PPV:PCBM) bulk heterojunction solar cells in the dark and under illumination are described. Using numerical modeling a fully quantitative explanation for the contrast and shifts of the surface potential in dark and light is provided. Under illumination an excess of photogenerated electrons is present in both the donor and acceptor phases. From the time evolution of the surface potential after switching off the light the contributions of free and trapped electrons can be identified. Based on these measurements the relative 3D energy level shifts of the sample are calculated. Moreover, by comparing devices with fine and coarse phase separation, it is found that the inferior performance of the latter devices is, at least partially, due to poor electron transport.
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| 10. |
- Stuhr-Hansen, Nicolai, et al.
(författare)
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Organoselenium-Substituted Poly(p-phenylenevinylene)
- 2005
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Ingår i: Heteroatom Chemistry. - : Wiley. - 1042-7163 .- 1098-1071. ; 16:7, s. 656-662
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Tidskriftsartikel (refereegranskat)abstract
- A new type of conjugated polymer, organoselenium substituted poly(p-pheylenevinylene) (PPV), was synthesized from the corresponding alkylselenenyl p-xylylene dibromide via a Gilch route using potassium tert-butoxide in THF. The p-xylylene dibromide precursors were synthesized by reacting lithiated bis(methoxymethyl)benzenes with elemental selenium, followed by alkylation of the generated selenolates. As a final demasking step, the bromomethyl functions were liberated by ether cleavage using boron tribromide. Bis-alkylselenenyl PPV was obtained with an average molecular weight Mw of approximately 300,000 g/mol and with polydispersity Mw/Mn=2. Due to low solubility, monoalkylselenenyl PPV was obtained with a considerably lower average molecular weight in the proximity of 16,000 g/mol and with a polydispersity slightly larger than 3. Absorption and flourescence spectroscopy revealed that the bis-alkylselenenyl PPV is extensively conjugated.
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