| 1. |
- Roelofs, W.S. Christian, et al.
(författare)
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Scanning tunnelling microscopy on organic field-effect transistors based on intrinsic pentacene
- 2014
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 104:26, s. 263301-
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Tidskriftsartikel (refereegranskat)abstract
- The full potential of scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy for in-situ characterization of organic semiconductors has so far not been accessible. Here, we demonstrate that the underlying problem, the low intrinsic conductivity, can be overcome by working in a field-effect geometry. We present high resolution surface topographies obtained by STM on pentacene organic field-effect transistors (OFETs). By virtue of the OFET geometry, the hole accumulation layer that is present at sufficiently negative gate bias acts as back contact, collecting the tunnelling current. The presence of a true tunnelling gap is established, as is the need for the presence of an accumulation layer. The tunnelling current vs. tip bias showed rectifying behaviour, which is rationalized in terms of the tip acting as a second gate on the unipolar semiconductor. An explanatory band diagram is presented. The measurements shown indicate that intrinsic organic semiconductors can be in-situ characterized with high spatial and energetic resolution in functional devices.
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| 2. |
- Charrier, Dimitri S. H., et al.
(författare)
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Large Electrically Induced Height and Volume Changes in Poly(3,4-ethylenedioxythiophene)/Poly(styrenesulfonate) Thin Films
- 2010
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Ingår i: Chemistry of Materials. - : American Chemical Society. - 0897-4756 .- 1520-5002. ; 22:12, s. 3670-3677
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate large, partly reversible height and volume changes of thin films of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) on the anode of interdigitating gold electrodes under ambient conditions by applying an electrical bias. The height and volume changes were monitored with optical and atomic force microscopy and are found to be independent of initial film thickness. In the first cycle, a relative height change of 950% is observed for a 21 nm thick film. Two regimes are identified. In the first regime, reversible redox reactions occur and reversible height changes can be ascribed to absorption of water via osmotic effects, brought about by an increasing ion concentration on the anode. In the second, irreversible regime, irreversible overoxidation of the PEDOT occurs and mass transport from the channel to the anode becomes important.
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| 3. |
- 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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| 4. |
- 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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